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MOTOR VEHICLES

and THEIR ENGINES

A Practical Handbook on the CARE, REPAIR and MANAGEMENT

OF

MOTOR TRUCKS and AUTOMOBILES

for Owners, Chauffeurs, Garagemen and Schools BY

EDWARD S. ERASER

American Bosch Magneto Corporation; Formerly, Captain, C. A., U. S. A. Instructor Motor Transportation Course, Coast Artillery School

AND

RALPH B. JONES

Willys Overland Company; Formerly, Captain C. A., U. S. A. Instructor Motor TradspgostatiQn, Qpurse, Coas,t, Artillery School

278 ILLUSTRATIONS

NEW YORK

D. VAN NOSTRAND COMPANY

EIGHT WARREN STREET

1921

•P?

Copyright 1919, by D. VAN NOSTRAND COMPANY

Printed in the U. S. A.

PREFACE

The following pages represent the result of an attempt to collect in a comparatively small book such elementary, theoretical, and practical information as will assist in the operation, upkeep, and adjustment of the motor vehicles. This book was written with a three-fold purpose; as a guide for the personal instruction of the car owner, as a hand book for chauffeurs, garages, and repairmen, and as a text book for Automobile Schools. The simplest language has been used and technicalities have been reduced to a minimum. The fundamentals of gas motor operation, as well as the care and opera- tion of the principal accessories of the motor vehicles concerned, are discussed in detail and at greater length than is the usual practice.

To' obtain the maximum economy, efficiency, and life of the apparatus the last four chapters of the book should be studied. These chapters are the result of the authors' observations and expe- rience with the great number of trucks, tractors, automobiles, and motor-cycles operating under their supervision.

This book is the outgrowth of the authors' former volume " Motor Transportation for Heavy Artillery," which was prepared for use as a textbook in the Coast Artillery School's course in the subject. The valuable experience gained in connection with their work as instructors in this school has been embodied in this second edition so that the book contains all the information necessary to properly operate and care for motor vehicles.

The authors wish to express their indebtedness to the Norman W. Henley Publishing Company for permission to use figures 6, 7, 46, 136, 215, 237, 246, 252, 260, 262, 263, 266 and 268 from Page's " Modern Gasolene Automobile."

April, 1920. THE AUTHORS.

CONTENTS

CHAPTER PAGE

\ I THE GAS ENGINE 1

i- II PRINCIPLES OF Two AND FOUK-CYCLE ENGINES 8

(( III TIMING 14

IV ENGINE BALANCE AND FIRING ORDER 21

V COOLING SYSTEMS 34

VI FUEL FEED SYSTEMS 48

VII FUELS 55

VIII ELEMENTS OF CARBURETION 63

IX CARBURETORS 72

X CARBURETORS (Continued) 89

XI PUDDLE TYPE CARBURETORS 114

XII MAGNETISM 117

XIII ELEMENTARY ELECTRICITY 128

XIV BATTERIES 135

XV INDUCTION 146

XVI BATTERY IGNITION SYSTEMS 151

XVII MAGNETOS: ARMATURE TYPE 172

XVIII MAGNETOS: ROTOR TYPE 193

-S XIX DUAL AND DUPLEX IGNITION SYSTEMS 201

XX STARTING AND LIGHTING SYSTEMS 207

XXI POWER TRANSMISSION 227

XXII CLUTCHES 232

XXIII TRANSMISSIONS 241

XXIV DRIVES 258

XXV DIFFERENTIALS 263

XXVI RUNNING GEAR 270

XXVII TIRES AND RIMS 289

XXVIII How TO DRIVE 299

XXIX ENGINE TROUBLES EXPERIENCED ON THE ROAD 303

XXX LUBRICATION 309

XXXI CARE AND ADJUSTMENT. . 317-ltf-l^

3T3-<*

XXXII CARE AND ADJUSTMENT TABLES 329

INDEX .345

MOTOR VEHICLES

AND THEIR ENGINES

CHAPTER I

THE GAS ENGINE M - *'- - '' •

The term "Gas Engine" is commonly used to designate all types of internal combustion engines regardless of whether they operate on gas or liquid fuel. Liquid fuel is almost universally used in engines adapted for motor transportation. GasolirTe is the most commonly used liquid fuel. Kerosene, alcohol, benzol, and fuel oil are used in internal combustion engines, but in general their use is confined to engines of the stationary type.

In the internal combustion engine, the fuel is introduced into the cylinder in a combustible mixture and is there ignited. This type of engine is divided into two classes, that in which the combustion takes place gradually and that in which the combustion takes place almost instantaneously.

The Diesel engine comes under the class in which the combustion is gradual. The liquid fuel is gradually injected into the cylinder which contains only air under high pressure. This air is compressed to such a degree that a temperature far above the ignition point of the fuel is obtained. This causes the fuel to ignite as it is injected into the combustion space. Complete but gradual combustion is obtained in this manner. Engines of this type are not applicable for motor propelled vehicles, largely because of their lack of flexibility.

In the gasoline engine the fuel is burned almost instantaneously. The air is mixed with the fuel outside of the combustion space (Fig. 1) and the resulting combustible mixture is drawn into the cylinder where it is ignited under compression by some outside source of heat., the electric spark being the one universally adopted.

Combustion or burning is always accompanied by the production of heat. The temperature produced depends upon the rapidity and completeness of the combustion. The faster the burning the higher the maximum temperature produced. A slow burning fuel produces a more uniform temperature, but not as high as is produced by a fuel burning almost instantaneously.

MOTOR VEHICLES AND THEIR ENGINES

CRAM SHAFT BMniNG- CflAflK MSF ^£»HMJrmr£ CAn fWMSI CM SHAFT GEM

Fig. 1 — Engine Parts

WORKING PARTS: Pistons

Piston rings

Wrist pins Connecting rods

Connecting rod caps

Shims

Connecting rod bearings Crank shaft

Gear to cam shaft

Crank arms

Crank pins

Journal

Fly wheel

VALVE MECHANISM:

Cam shaft

Cam shaft gears

Inlet cams

Exhaust cams Push rods (lifter rods or tappets)

Roller or mushroom head

Adjusting nuts Valves

Valve stem

Valve spring

Valve head

Valve clearance

ENGINE NOMENCLATURE

Fan Support »» Fun tfl«<le<i

Oil Wvll<SsF^ _ fi /

•~<MT»~»-£r ^^Or^n^

Fig. 2 — Sectional View of Typical Four-Stroke Cycle, Four-Cylinder

Motor Truck Engine, Showing Important Internal Parts

and Their Relation to Each Other

STATIONARY PARTS

Cylinder casting

Water jacket

Inlet ports

Exhaust ports

Valve seats

Cylinder head

Combustion space Crank case

Upper half

Lower half

Lifter guides

Main bearings

Cam shaft bearings

Oil reservoir

Oil pump

Float

Gear cover

Breather tube

ACCESSORIES: Inlet manifold Exhaust manifold Fan assembly

Fan

Pulley

Belt

Bracket Starting crank Valve caps Spark plugs

Compression cocks (priming cocks) Water pumps

Magneto or timer-distributor Carburetor

4 MOTOR VEHICLES AND THEIR ENGINES

When gases and most metals are heated they expand, some ex- panding more than others. Gases expand more than metals for a given amount of heat. A definite increase of temperature will cause a gas to expand a certain amount and as the heat is increased the expansion increases in proportion. When the mixture in the cylinder is burned, the resulting heat causes the gases to expand, the amount of this expansion depending upon the temperature.

When a gas contained in a closed vessel is heated its expansion exerts a pressure equally in all directions. This condition exists in the cylinder of an internal combustion engine after combustion has taken place. The resulting pressure is exerted on the cylinder walls and piston. The piston, being movable, under the force of the expanding gases, moves outward to the full limit of its stroke.

The energy resulting from this expansion must now be trans- formed into useful work. In order to accomplish this, a construction such as shown in Fig. 3 is used.

The force exerted on the piston "K" is transmitted through the connecting rod "E" to the crank shaft UH" which is made to revolve, turning through one-half of a revolution as the piston moves out- ward. Attached to the crank shaft is a fly wheel, which stores up energy and its momentum carries the piston through the balance of its motion until it receives another power impulse. In this way the reciprocating motion of the piston is transformed into a rotary motion at the crank shaft.

The operation of the gasoline engine, as already shown, depends upon the production of heat in the cylinder caused by burning the

Fig. 3— Engine Operation

THE GAS ENGINE

.EXHAUST GAS, DIRECT RADIATION

35.6%

POWEHOF CAR

12.5%

EXCESS POWER FOR ACCELERATION. HILLS. ETC.

5-4%

FRONT WHEEL*

0.6%

AIR RESISTANCE 7.1%

Fig. 4 — Energy Diagram

6 MOTOR VEHICLES AND THEIR ENGINES

fuel. A given amount of fuel will produce a certain amount of heat when completely burned. However, the total heat value of the fuel cannot be utilized because there are certain losses which must always occur even in the best designed engine. Badly worn engines, im- perfect carburetion, and faulty ignition will add to the necessary losses and decrease the percentage of energy actually available for useful work.

The highest thermal efficiency attained in the best types of large stationary internal combustion engines (Diesel) is about 35% while few automobile engines ever exceed 20%. The diagram (Fig. 4) shows the dispersion of energy from fuel as it passes through the engine of a high class touring car traveling at a speed of 40 miles per hour on direct drive.

Referring to Fig. 4, it will be seen that a certain amount of the heat is absorbed by the cooling system. Also a considerable amount of heat is lost in the exhaust gases. Nearly 70% of the total fuel value is lost in this way and this loss cannot be materially reduced below this amount. The loss due to engine friction will vary con- siderably with the design and condition of the engine. The point indicated as " Motor Full Power" represents the amount of energy remaining for useful work. When this energy is applied to driving an automobile, it is consumed as shown in the diagram. This leaves but a small amount of reserve energy, which will be decreased as the speed of the machine is increased. Every design of engine and car of course has a different energy diagram corresponding to the degree of efficiency attained at different speed and loads.

Engines of all kinds are rated in horse-power — the measure of the rate at which they can do work. One horse-power represents 33,000 foot-pounds of work per minute. There are two ways of measuring engine power. The power developed by the expansion of the gases in the cylinder can be determined, in which case the INDICATED HORSE-POWER is obtained. By means of a Prony Brake or Dynamometer, the power which the engine actually delivers can be measured and this is called the BRAKE HORSE-POWER. The brake horse-power of an automobile engine will usually be from 70% to 85% of its indicated horse-power, the losses being energy consumed in friction and other causes in the engine mechanism. However, in obtaining the horse-power of an engine, formulae are used based on the indicated horse-power assuming certain standard conditions. The horse-power obtained in this manner is often incon- sistent with the actual horse-power developed on test.

There are a number of quick rules for estimating the power of engines according to their cylinder dimensions and the piston speed.

THE GAS ENGINE

*

The one most used for four-cycle engines is given below. The simplest formula is that of the Society of Automobile Engineers:

..

2.5 The formula for finding the indicated horse-power of an engine is :

I. H. P. (for 1 Cylinder) = R A' S'

33,000x4

Where P = mean effective pressure in pounds per square inch. A = piston area in square inches. S = piston speed in feet per minute.

Where the engine has more than one cylinder, the result ob- tained from this formula must be multiplied by the number of cylinders. The brake horse-power is obtained by multiplying by the mechanical efficiency of the engine. The complete equation for brake horse-power is:

BHp=P.A.S.N.E.

33,000 x 4

Where N == number of cylinders. E = mechanical efficiency.

Assuming a mean effective pressure of 90 pounds per square inch, a piston speed of 1,000 feet per minute, and a mechanical efficiency of 75% and substituting these values in the formula for brake horse-power, the following value is obtained:

D2N D2N

B. H. P. = - or approximately - 2.489 2.5

Where D = diameter of piston in inches.

This is the S. A. E. formula for four-cycle engines

For two-cycle engines this becomes:

1.5

CHAPTER II

PRINCIPLES OF TWO AND FOUR-CYCLE ENGINES

In order that the operation of the gas engine be continuous, a certain series of events called the cycle must take place which are repeated over and over in the same regular order. In order to clearly understand the events that compose the cycle of an engine, its opera- tion will be compared to the operation of the old style muzzle-loading cannon, which is the simplest form of internal combustion engine.

Referring to Fig. 5, the first step necessary to fire the cannon is inserting the charge; the corresponding step in the gas engine is the ADMISSION of the charge. The second step is ramming the pro- jectile and powder; the corresponding step in the gas engine is the COMPRESSION of the charge. The third step is lighting the fuse; the corresponding step in the gas engine is the IGNITION of the charge. The fourth step is burning the powder and the fifth step expansion of the gases of combustion due to the heat produced which forces the projectile out of the cannon. The corresponding steps in the gas engine are the COMBUSTION of the charge and EXPAN- SION of the gases. The sixth step in the operation of the cannon is the escape of the burned gases after the projectile has left the muzzle; the corresponding step in the gas engine is the subsequent EXHAUST of the products of combustion. The cannon is now ready to be fired again and the engine to continue its operation.

The steps comprising the cycle of operation of the gas engine may be summarized as follows :

1. Admission of the charge.

2. Compression of the charge.

3. Ignition of the charge.

4. Combustion of the charge.

5. Expansion of the gases.

6. Exhaust of the gases.

In the operation of a gas engine the number of strokes required to complete the cycle varies with the type of engine. In the type almost universally used for motor vehicles the cycle is extended through four strokes of the piston or two revolutions of the crank shaft and is therefore called a four-cycle engine. In a few instances the cycle is completed in two strokes of the piston or one revolution of the crank shaft and is therefore called a two-cycle engine.

B

D

Fig. 5 — Operation of Cannon and Engine Compared

0

10 MOTOR VEHICLES AND THEIR ENGINES

FOUR-CYCLE ENGINES

In the four-cycle engine, the four strokes are named suction, compression, power, and exhaust in accordance with the operations of the cycle which occur during each particular stroke.

SUCTION STROKE.— During this stroke (Fig. 5-A) the piston is moved outward by the crank shaft which is either revolved by the momentum of the fly wheel or some external starting force. This movement of the piston increases the size of the combustion space, thereby reducing the pressure in it and the higher pressure of the atmosphere outside, forces fresh mixture into the combustion space through the open inlet valve.

COMPRESSION STROKE.— The compression, ignition, and most of the combustion of the charge takes place during the next inward stroke of the piston. The time elapsed between the mixing of the liquid gasoline and air and its admission into the cylinder is too brief to secure a perfect combustible mixture. What passes into the cylinder consists of air, liquid gasoline, and a more or less perfect mixture of the two. The combustion of this mixture would be slow and incomplete resulting in a loss of power and a waste of fuel. In order to obtain a homogeneous mixture, advantage is taken of the heat produced by compression. This renders the gasoline more volatile, while the compression forces it into intimate combina- tion with the air. Even then a perfect mixture may not result for the air and gasoline vapor instead of being thoroughly combined may be in layers. The combustion will then be slow and uneven. When the mixture of air and gasoline vapor are properly proportioned, this difficulty is seldom encountered. The mixture is ignited while under compression and combustion is practically completed at top dead center.

POWER STROKE.— The expansion of the gases due to the heat of combustion exerts a pressure in the cylinder and on the piston. Under this impulse it moves outward.

EXHAUST STROKE.— When the exhaust valve is opened, the greater part of the burned gases escape due to their own expansion. The inward movement of the piston pushes the remaining gases out of the open exhaust valve. The space between the cylinder head and the piston, when it is at its inmost point, is called the clearance and will be filled with the remaining exhaust gases. These will dilute the fresh incoming charge.

Thus it is seen that in this type of engine four strokes of the piston are required to complete the cycle.

PRINCIPLES OF TWO AND FOUR-CYCLE ENGINES 11

Fig. 6 — Three-Port Two-Cycle Engine

TWO-CYCLE ENGINES

The two-cycle type of gasoline engine differs from the four-cycle type just described in that the six events composing the cycle are performed during two strokes of the piston or one revolution of the crank shaft. Power is developed during every outward stroke of the piston instead of alternate outward strokes.

In order that this result may be attained, the construction of the engine is changed. As shown in Fig. 6, the crank case is utilized as a receiver for the mixture before it passes to the combustion space. The valves are replaced by ports, which are openings into the com- bustion space. These are covered and uncovered by the piston as it slides in the cylinder. The gas inlet port to the crank case is uncovered when the piston is at the inmost point of its stroke ad- mitting the mixture to the crank case. This is air tight and must have a separate compartment for each cylinder. The exhaust port and the intake port are uncovered when the piston is at the outmost point of its stroke. The exhaust port opens first, which permits the burned gases to escape after combustion has taken place. The intake port opens shortly after the opening of the exhaust port and permits a fresh charge to pass from the crank case to the combustion space.

During an inward stroke, the pressure in the crank case is reduced as the piston moves inward and a fresh mixture is forced into it by the higher atmospheric pressure as soon as the gas inlet is uncovered. This port is covered when the piston makes an outward stroke and the mixture, not being able to escape, is compressed. The tendency

12

MOTOR VEHICLES AND THEIR ENGINES

of the gas to expand causes it to flow to the combustion space when the inlet port is uncovered, and in entering, it strikes a deflecting plate on the piston. This deflects it to the top of the combustion space instead of allowing it to rush across the cylinder and out the open exhaust port. The inward stroke of the piston covers these two ports and compresses the mixture, ignition occurring in the regular manner. The pressure developed by the combustion drives the piston outward. As soon as the exhaust port is uncovered, which is slightly before the uncovering of the inlet port, the gases, which are still expanding, begin to escape. They are further expelled by the fresh charge that enters and drives them before it. Thus the six events of the cycle are performed during an inward and an out-

Fig. 7 — Two-Port Two-Cycle Engine

ward stroke of the piston. On the lower side of the piston a charge of fresh mixture is drawn into the crank case and forced into the combustion space where it is compressed, ignited, and burned.

The type of engine just explained is known as the three-port construction of two-cycle engine. There is also a two-port construc- tion of two-cycle engine. This type of engine differs from the three port in that the inlet port to the crank case is replaced by a check valve as shown in Fig. 7. When the pressure in the crank case is reduced due to the piston moving inward, the higher atmospheric pressure opens the valve and forces a fresh mixture into the crank case. The valve is closed by the action of the spring at all other times and is further assisted in closing by compression in the crank

PRINCIPLES OF TWO AND FOUR-CYCLE ENGINES 13

case. The operation of this engine is identical in all other respects with the three-port construction.

In all two-cycle engines a screen is placed in the bypass. The object of this is to prevent any possibility of the incoming charge being ignited by the exhaust gases thus causing a back fire into the crank case.

At slow speeds, two-cycle engines have advantages over the four- cycle in having a power impulse every revolution of the crank shaft and in not having valves and valve mechanism with their weight and possibility of giving trouble. This simplicity makes the two-cycle engine popular for motor boats, where slow and constant speeds are desired. For higher and changing speeds these advantages are out- weighed by disadvantages that show little sign of being overcome.

With the engine running at high speed, the ports are open for only a brief period during each stroke, and the faster the engine runs, the shorter will be the period during which the gases may enter or leave the combustion space. The inefficiency of two-cycle engines as compared with engines of the four-cycle type is due entirely to the fact that the burned gases have not sufficient time in which to escape from the combustion space, nor the fresh charge time to enter. The fresh charge that does enter is incomplete and contaminated by the portion of the burned gases that have not been able to escape. This results in the "choking up" of the engine, and in the production of lower power than the dimensions and weight of the engine warrant.

Automobile engineers agree that the four-cycle engine is better for automobile work. It has been developed to a greater degree than the two-cycle and it is easier to keep adjusted and in good running condition. Though the two-cycle engine is undoubtedly the simplest form, it is liable to be erratic in operation and it is some- times difficult to locate the trouble definitely. The following ad- vantages are claimed for the two-cycle engine over the four-cycle:

(1) absence of poppet valves with their springs, push rods, cam shafts, etc.; (2) fewer parts; (3) better turning effect with the same number of cylinders. Offsetting these, the four-cycle engine has the following advantages over the two-cycle: (1) greater fuel economy,

(2) greater flexibility. These advantages far over-balance the advantages of the two-cycle over the four-cycle engine and for that reason the two-cycle engine is very rarely used for automobile propulsion.

CHAPTER III

TIMING

As explained in the operation of the four-cycle engine, the inlet valve is opened during the suction stroke and the exhaust valve is opened during the exhaust stroke. In this chapter will be shown the exact time at which the valves open and close with reference to the position of the piston. In outlining the timing of the valves, the reason for each operation of the valve will be explained.

During the inlet stroke, the inlet valve must be open to admit the charge. The charge is forced into the cylinder due to the pres- sure being reduced as the piston moves outward. If the inlet valve were opened at top dead center, the gases would not be forced into the cylinder until the piston had moved out sufficiently to cause a decrease in pressure and the velocity of the incoming gases for some time would be slow. In order to prevent this, the inlet valve remains closed for a certain number of degrees during the downward move ment of the piston. This causes a sufficient decrease in pressure to allow the gases to be forced in with a certain amount of initial velocity. Most manufacturers have adopted this practice as the cylinder will be filled more rapidly.

The rapid decrease in pressure in the cylinder due to the outward movement of the piston causes the gases to rush in and fill up the space back of the piston. If the piston moves slowly, the mixture will be able to enter fast enough to keep the pressure in the com- bustion space equal to that outside. At the high speed at which a gasoline engine runs, the piston will reach the end of its stroke before a complete charge has had time to enter through the small inlet valve opening. Therefore the pressure in the combustion space will still be below that of the atmosphere. If the inlet valve closed at this point so that no more mixture could enter, the combustion of the partial charge would result in a lower pressure than would be possible with a full charge. The inlet valve should therefore remain open until the piston reaches a point in its next inward stroke at which the pressure in the cylinder equals that outside. The piston moving inward diminishes the space in the cylinder and compresses the gas ahead of it. When under compression, the gas is ready to be ignited and burned.

The combustion of the inflammable mixture produces a certain amount of heat. The more rapid and complete this combustion, the

14

TIMING 15

greater and more sudden will be the rise in pressure. The pressure will be greater when the mixture is contained in a small space than when in a large space. As the combustion space is smallest when the piston is at its inmost point, the greatest pressure will be obtained if combustion is completed at this pointc If the combustion of the mixture were instantaneous, it would be ignited at this point. But even though very rapid, it burns slowly enough to make necessary the ignition of the mixture before the end of the stroke. The com- bustion will then be complete as the piston comes into position to move outward. The instant at which the mixture must be ignited in order to produce this result depends on the speed of the piston. The interval between the ignition of a good mixture and its complete combustion does not vary to any great extent. When the piston is moving slowly, the mixture may be ignited toward the end of the compression stroke, for there will be sufficient time for complete combustion by the time the stroke is ended. When moving at high speed, ignition must occur much earlier in the stroke, as otherwise the piston will have completed the compression stroke and begun to move outward on the power stroke before the mixture is entirely burned. The instant at which ignition occurs also depends on the mixture that is used, since this makes a difference in the rapidity with which it burns. The better the quality of the mixture, the faster and more completely it will burn and ignition may occur later in the stroke than would be possible with a mixture of poorer quality. The instant at which ignition occurs may be controlled by causing the spark to take place earlier or later, this being controlled by the driver.

When ignition occurs early in the compression stroke, the spark is said to be advanced. A retarded spark takes place when the com- pression stroke is more nearly complete.

If the spark is advanced too much, combustion will be complete before the piston has reached the end of the compression stroke. It will then be necessary to force the piston inward against the resultant pressure by the momentum of the flywheel, in order that it may get into position to move outward on the power stroke. In such a case, the momentum may not be sufficient to overcome the pressure and the piston will be brought to a stop.

A retarded spark often results in the complete combustion of the mixture after the piston has begun to move outward on the power stroke. The pressure will then be reduced because combustion takes place in a larger space, the piston consequently being moved with less force. If the spark is still further retarded, the combustion will not be completed by the time exhaust begins. The heat from only

16 MOTOR VEHICLES AND THEIR ENGINES

a portion of the mixture will then be utilized because the gases will still be burning as they are forced out of the cylinder.

The position at which the spark occurs should be governed by the speed of the engine. The low pressure that results from a retarded spark moves the piston at low speed, while the high pressure from an advanced spark drives the piston outward with more force and greater velocity.

While high compression of the charge improves its quality and results in combustion being more rapid and complete, it has limits, and if carried too far the heat generated by the compression will be sufficient to ignite the mixture. This would have a bad effect on the operation of the engine, for the pressure would then be produced at the wrong point in the stroke, retarding instead of assisting the revolution of the crank shaft.

As the piston is forced outward by the expanding gases, it has been found necessary to open the exhaust valve before the piston reaches the end of its stroke. Even if this wastes some of the force of the expansion, it is amply compensated for by the freedom afforded the piston in commencing the exhaust stroke. By opening the exhaust valve, before the piston reaches the end of its power stroke, the gases will have an outlet for expansion and begin to rush out of their own accord. This removes the greater part of the burned gases, reducing the amount of work to be done by the piston on its return stroke. Obviously it would be wrong to keep the exhaust valve closed up to the very moment when the piston is about to move inward. When commencing the exhaust stroke, the piston would be confronted for an instant with the force which had just driven it down and until the valve was wide open there would be a considerable loss of power. If the exhaust valve opens too early, there will be a waste of power because the gases exhausted could still have exerted a pressure on the piston. During the next inward stroke, the remaining gases are forced out of the open exhaust valve as the pressure in the cylinder exceeds that in the exhaust manifold. This causes a slight compression of the gases ahead of the piston and when it reaches its inmost position there will be a certain amount of compressed exhaust gases in the clearance space.

If the exhaust valve is closed at this point, a portion of these gases will still be retained in the cylinder. The best results are obtained, not by closing the exhaust valve at the end of the exhaust stroke, but at a short time after the piston has begun to move out- ward. It would appear that this would result in drawing the exhaust gases back into the cylinder. However, this is governed by two conditions: first, the gases under compression exceed the pressure

TIMING

17

H^,,,:

"""X

Fig. 8— Rock of Piston

in the exhaust manifold and will continue to flow out due to this difference in pressure; second, the piston while at the top of the stroke moves but very little for 10 to 15 degrees movement of the crank shaft. This does not materially increase the combustion space.

It will be seen that this is true by referring to Fig. 8. When the crank arms are in a position as shown at A, for a certain number of degrees movement of the crank shaft, the piston will move upward for a certain distance. When the crank arms are at point B, for the same number of degrees movement of the crank shaft, the dis- tance moved by the piston will be less. When the crank arms are at point C, for the same number of degrees there is very little upward movement of the piston. Between certain points it can be seen that there is practically no motion of the piston which is called the "rock of the piston." This is usually the amount that the exhaust valve is left open after top dead center.

Diagrams showing the exact timing of the valves on several en- gines are shown in Figs. 9 to 12, inclusive. From these diagrams, comparisons may be made as to the time the valves open and close in different designs of engine.

Referring to the valve timing diagrams, it will be seen that the point at which the inlet valve opens is approximately the same on these four standard engines which are designed to run at different speeds and for different kinds of work. On practically all engines, the inlet valves open approximately 11 degrees after top dead center.

The point at which an inlet valve closes depends upon a great many conditions, the principal ones being the maximum speed for which the engine is designed and the size and location of the valves. The average point for closing the inlet valve is about 35 degrees

18

MOTOR VEHICLES AND THEIR ENGINES

B. AC.

Fig. 9

HOLT

1. Inlet valve opens 10° after T. D. C.

2. Inlet valve closes 10° after B. D. C.

3. Exhaust valve opens 30° before B. D. C.

4. Exhaust valve closes 5° after T. D. C.

Fig. 10

DODGE 10° after T. D. C. 35° after B. D. C. 45° before B. D. C. 8° after T. D. C.

T.0.C.

•A AC.

Fig. 11

WHITE

1. Inlet valve opens 10° after T. D. C.

2. Inlet valve closes 40° after B. D. C.

3. Exhaust valve opens 40° before B. D. C.

4. Exhaust valve closes 8° after T. D. C.

Fig. 12

F. W. D.

15° after T. D. C. 45° after B. D. C. 45° before B. D. C. 10° after T. D. C

The above diagrams each represent the two revolutions of the crank shaft necessary to complete one cycle.

TIMING

19

after bottom dead center. The valve closes later on high speed engines and earlier on slow speed engines.

The point at which the exhaust valve opens also varies consider- ably and depends upon the same conditions as the closing of the inlet valve. The average point for opening the exhaust valve is 45 degrees before bottom dead center. It will be earlier on high speed engines and later on slow speed engines.

The exhaust valves of the engines represented in the timing diagrams all close at approximately the same point. This is true of practically all types of engines, the average point for closing the exhaust valve being 6 degrees after top dead center. This point is limited by the duration of the rock of the piston and hence cannot vary greatly.

Fig. 13 shows a valve timing diagram made up from the average points at which the valves open and close on engines of American design. It is a good guide for the approximate timing of the valves of an engine in case the exact timing is not known. However, it must never be used for accurately setting the valves on any engine.

1. Inlet opens 11° after T. D. C.

2. Inlet closes 35° after B. D. C.

3. Exhaust opens 45° before B. D. C.

4. Exhaust closes 6° after T. D. C. Suction 204° Compression 145°

Power 135°

Exhaust 231°

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Fig. 13 — Valve Timing of Average Engine

If for any reason it is necessary to disassemble the engine, the timing gears should be punched so as to indicate where they should mesh when they are again assembled in order to have the proper timing of the valves. If an engine is received with the flywheel unmarked, the first duty for the man in charge of the apparatus is to see that the flywheel is marked correctly in order to have some accur- ate method of checking up valve-timing and valve-clearance at all times. Marking the flywheel is a very simple matter and will elimi-

20 MOTOR VEHICLES AND THEIR ENGINES

nate endless trouble whenever any repairs are made to the engine where disassembling is necessary.

In case a crank shaft is offset from the center line of the cylinders, the exhaust valves will usually close at top dead center, as the rock of the piston at this point has been eliminated. The reason for such design is that when the maximum expansion occurs at top dead center, there will not be a direct downward thrust on the crank shaft and connecting rod bearings.

CHAPTER IV

ENGINE BALANCE AND FIRING ORDER

The term engine balance includes both power balance and me- chanical balance of the engine. An engine has power balance when the power impulses occur at regular intervals in relation to the revolu- tion of the crank shaft. In many types of engines the power impulses do not occur regularly and there is an uneven distribution of power. The power balance of various types of engines will be discussed in this chapter. An engine has mechanical balance when the moving parts are so arranged as to counterbalance in their operation and thereby reduce vibration.

The difficulty in constructing reciprocating engines is that the weight of the pistons and connecting rods in moving first one way and then the other, produces great vibration. The crank shaft in bringing these parts to a stop at the end of each stroke, is subjected to violent shocks which in time wear it loose in its bearings. With internal combustion engines, this vibration and the shock on the crank shaft are greatly increased by the intensity with which the pressure is exerted on the piston.

In a well-designed engine, the manufacturer is very careful to see that every piston and connecting rod is of identically the same weight and that the fly wheel and crank shaft have a perfect running balance. By this practice a considerable amount of the vibration will be eliminated.

In a one-cylinder engine (Fig. 14) there is but one power impulse during two revolutions of the crank shaft. Therefore there will be an uneven distribution of power. Since there is but one piston and connecting rod which reciprocate with no working parts to counter-

Fig. 14 — One-Cylinder Power Balance Chart 21

22

MOTOR VEHICLES AND THEIR ENGINES

balance their weight, the engine will not have mechanical balance. The engine can, however, be balanced to some extent by the use of counterweights attached to the crank shaft and also by the use of a fly wheel so heavy that its momentum produces a comparatively steady movement. Fluctuations in the speed of the engine will cause vibration even under the most favorable conditions which makes the one-cylinder engine undesirable for motor vehicles.

In two-cylinder engines, the vibration may be reduced by ar- ranging the parts so as to have the pistons move in opposite direc- tions, thus counterbalancing each other. This is the plan of con- struction used in the horizontal double opposed engine (Fig. 15). The cylinders are horizontal and arranged on opposite sides of a two-throw 180° crank shaft. That is, there are two pairs of crank

Fig. 15 — Two-Cylinder Opposed Power Balance Chart

arms projecting from opposite sides of the shaft so that they are one- half a revolution apart. An engine of this construction has good mechanical balance.

To fully understand the power balance as shown in the table, the order in which the strokes of a four-cycle engine occur must be recalled. The two outward strokes are suction and power and the two inward strokes compression and exhaust. If piston number one is moving outward on power, then piston number two must be moving out on suction, and for the next half revolution or inward strokes of the pistons, number one piston will be exhausting the gases while number two piston is compressing the charge. During the second revolution of the crank shaft, number two piston will move outward on power while number one moves outward on suction and during the in- ward strokes of the pistons, number two is exhausting the burned gases while number one is compressing a fresh charge. In this way, one power impulse is obtained during each revolution of the crank shaft. This engine has both power balance and mechanical balance.

Two-cylinder engines are also built with vertical cylinders and are classed according to the construction of their crank shafts. One

ENGINE BALANCE AND FIRING ORDER

23

has a 180° crank shaft which is identical with that used in the two- cylinder opposed engine. The other has a 360° crank shaft, which has both pairs of crank arms projecting from the same side of the shaft, so that the crank pins are in line.

Fig. 16— Two-Cylinder 180° Crank Shaft Power Balance Chart

In the two-cylinder 180° crank shaft construction (Fig. 16) number one piston is moving outward as number two piston is moving inward; in other words, the pistons move in opposite directions. An engine of this construction has good mechanical balance.

If piston number one is moving outward on power, piston number two can be moving inward either on compression or exhaust. In table one, the power balance is worked out with piston number two moving inward on compression and it is clearly shown that both power impulses occur during the first revolution while there are no power impulses during the second revolution. In table two the power balance is worked out with piston number two moving inward on exhaust. This arrangement gives a power impulse at the begin- ning of the first revolution and at the end of the second, producing the same result as obtained in table one. In either case there is an irregular production of power which sets up strains in the engine which causes it to run unevenly. This results in poor power balance.

In the two-cylinder vertical engine with a 360° crank shaft, the pistons move up and down together causing bad mechanical balance (Fig. 17).

With this arrangement the application of power may be evenly distributed for as number one piston moves outward on power, piston number two could move outward on either power or suction. There would be no advantage in having both cylinders firing at the same time, hence number two piston moves outwards on suction. As shown in the table, during the first revolution, number one piston is on power and exhaust while number two piston is on suction and compression. During the second revolution number one piston is

24

MOTOR VEHICLES AND THEIR ENGINES

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Fig. 17 — Two-Cylinder 360° Crank Shaft Power Balance Chart

on suction and compression while number two piston is on power and exhaust. With this, arrangement there is a power impulse at the beginning of each revolution of the crank shaft and the engine has power balance.

The defects of two-cylinder vertical engines with either design of crank shaft outweigh any possible advantage of that construction. The horizontal double opposed type with evenly occurring power impulses, mechanical balance, and simplicity of construction is frequently used on small trucks.

With a four-cylinder engine a 180° crank shaft is always used (Fig. 18). The crank arms for numbers one and four cylinders pro- ject in the same direction and the crank arms for numbers two and three cylinders project from the opposite side of the crank shaft. This arrangement is used in preference to having the cranks projecting alternately, that is, one and three to one side and two and four to the other, because greater vibration and strain on the crank shaft would result with this construction. The form of crank shaft commonly used does not permit a firing order of 1-2-3-4, but gives firing orders in which numbers one and four must fire alternately. The succession in which power strokes occur is called the firing order.

In the four-cylinder engine numbers one and four pistons are always moving in the opposite direction from numbers two and three. If equal in weight they will balance each other and an engine of this type is said to have good mechanical balance.

As number one piston is moving outward on power, number four must move outward on suction; number two piston can be moving inward on exhaust or compression and number three will be moving inward on compression or exhaust. Table one shows the power balance with number two piston on exhaust and number three on compression. Table two shows the power balance resulting from number two piston moving inward on compression and number.

ENGINE BALANCE AND FIRING ORDER

25

three on exhaust. With either arrangement the power impulses are evenly distributed, that is, they are 180° apart.

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Each arrangement gives a different firing order. With the arrangement shown in table one the firing orders is 1-3-4-2. With the arrangement shown in table two the firing order is 1-2-4-3. Following are the firing orders of four-cylinder engines in several motor vehicles. It will be noted that the firing order 1-3-4-2 is the most common.

Four-Wheel Artillery Tractor 1-3-4-2

F. W. D. 1-3-4-2

Nash .... White. . . . Dodge

Standardized "B" Holt .... Packard . Ford .

1-3-4-2 1-3-4-2 1-3-4-2 1-3-4-2 1-2-4-3 1-2-4-3 1-2-4-3

Three-cylinder engines are built with 120° crank shafts, that is, the crank arms are J^ of a revolution apart instead of J^ revolution

26

MOTOR VEHICLES AND THEIR ENGINES

as in the 180° crank shafts. With this arrangement as shown in Fig. 19, number one piston moves outward on power, number two piston moves inward finishing its exhaust stroke and starts outward

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on suction, number three piston moves outward finishing its suction stroke and starts inward on compression. As number one piston moves inward on exhaust, number two piston finishes its suction stroke and starts inward OR compression, number three piston finishes its compression stroke and moves outward on power. As number one piston moves outward on suction, number two piston finishes its compression stroke and starts outward on power, number three piston finishes its power stroke and moves inward on exhaust. As number one piston moves inward on compression, number two .piston finishes its power stroke and starts inward on exhaust, number three piston finishes the exhaust stroke and starts outward on suction. From the foregoing it can readily be seen that the power impulses will occur every 240° movement of the crank shaft. An engine of this type has power balance.

Six-cylinder engines have crank shafts of a similar construction to the three-cylinder; having numbers one and six, two and five, and three and four pistons operating together. With this construction there will be six power impulses during two revolutions which gives very good engine balance.

In Fig. 20 it will be seen that as numbers one and six pistons are starting outward, numbers two and five are completing their outward strokes, and numbers three and four are on their inward strokes. With this arrangement it is possible to obtain four different combina- tions as shown in tables one, two, three, and four. It is also possible to have numbers three and four pistons finishing their outward strokes as numbers one and six start outward and two and five complete their inward strokes. Combinations as shown in tables five, six, seven, and eight will result. With any of these combinations it can be

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Fig. 20 — Six-Cylinder Power Balance Charts

27

28 MOTOR VEHICLES AND THEIR ENGINES

readily seen that the power impulses are evenly distributed and are 120° apart, the only difference being the order in which the cylinders fire.

Table 1.— Firing Order 1-3-5-6-4-2 Table 2.— Firing Order 1-4-5-6-3-^- Table 3.— Firing Order 1-3-2-6-4-5 wTable 4.— Firing Order 1-4-2-6-3-5 Table 5.— Firing Order 1-2-4-6-5-3 Table 6.— Firing Order 1-5-4-6-2-3 Table 7.— Firing Order 1-2-3-6-5-4- V Table 8.— Firing Order 1-5-3-6-2-4

Although there are eight possible firing orders there are only four which are commonly used. The following are seldom used: l_2_3_6-5-4, 1-5-4-6-2-3, 1-3-2-6-4-5, and 1-4-5-6-3-2. With any of these firing orders the three-cylinder at one end of the crank shaft fire and then the three at the other end fire, setting up vibration due to the concentration of the power impulses. For this reason, six-cylinder engines are commonly built to fire so that the impulses are. evenly distributed along the crank shaft.

Eight-cylinder engines for motor vehicles are usually constructed by arranging two four-cylinder engines to operate from a single four- throw 180° crank shaft of the same form used in the four-cylinder engine. The cylinders are set so that their center lines form an angle 90° and for this reason such engines are called "V Type." The con- necting rods of the cylinders on the right operate on the same crank pins as the corresponding connecting rods for the cylinders on the left. It must be borne in mind that these connecting rods operate independently of each other. Therefore the operations of the cylinders on the right are always 90° different from the cylinders on the left, that is, when number one piston on the right is at top dead center, number one piston on the left will have completed one-half its stroke (Fig. 21).

The table showing the power balance is based on the arrangement used in the Cadillac "8." As number one piston on the left is moving outward on power, number four piston on the left is mov- ing outward on suction, number two piston on the left moving in- ward on exhaust, and number three piston on the left moving inward on compression. The movements on the right hand side will be half completed, therefore, number one piston will be completing suction, number four piston will be completing power, number two piston will be completing compression, and number three piston will be completing exhaust. Working out the operations for each 90° move- ment of the crank shaft will give the results shown in the table.

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29

30 MOTOR VEHICLES AND THEIR ENGINES

There is a power impulse for every 90° movement of the crank shaft, giving a firing order as follows : lL-2R-3L-lR-4Lr-3R-2L-4R. The power impulses are regular and very frequent in an engine of this type insuring very good engine balance.

The twelve-cylinder engine is also a "V Type" and consists of two sets of six cylinders arranged similarly to the "V Type" eight- cylinder engine except that the angle between the center lines of the cylinders is 60°. A regular six-throw 120° crank shaft is used, two connecting rods being attached to each crank pin (Fig. 22). The table shown is based on the arrangement used in the Packard Twin Six; starting with number one piston on the right at top dead center and moving the engine 60° or one-third of a complete stroke and showing the changes that take place. This table shows that a fresh power impulse is given the crank shaft for each 60° movement which gives unusually good engine balance. The firing order of this engiue is lR-6L-4R-3L-2R-5L-6R-lLr-3R-4Lr-5R-2L.

There are many possible firing orders for eight and twelve- cylinder "V Type" engines other than the ones given. The firing order depends upon the arrangement of the cams on the cam shaft and any combination will give equally good power balance.

The one-cylinder engine having but one power impulse for two revolutions of the crank shaft does not run smoothly or quietly due to the size of the cylinder and time between impulses. This fact led to the adoption of the two, four, and six-cylinder engines and quite recently, the eight and twelve-cylinder engines have come into use. As the number of cylinders is increased, the power impulses increase in frequency. The average power is greater and above^four cylinders there is no period during which some cylinder is not delivering power. This means that in a six, eight, or twelve-cylinder engine there is no time at which the fly wheel must supply all the power required to maintain the engine speed.

The multi-cylinder engine, therefore, furnishes a practically con- tinuous flow of power with little vibration. The increase in the number of cylinders permits reduction in the size of each cylinder and this combined with the steady operation of the engine makes the modern automobile engine a very quiet, smooth-running, power unit.

As shown in valve timing, the average length of the power impulse is 145° and from Fig. 23 it can be seen that as the number of cylinders is increased the power impulses extend over a greater range. For engines having more than four cylinders the power impulses are con- tinuous and overlap, the length of overlap increasing with the number of cylinders.

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32

ENGINE BALANCE AND FIRING ORDER 33

Engines of more than four cylinders will have several possible firing orders. The exact firing order of the engine will depend upon the arrangement of the cams on the cam shaft. Therefore, the firing order can be determined by checking a certain operation of the valves such as the opening of the inlet or the opening of the exhaust, or by checking the compression. The firing order thus obtained will cor- respond to that of the power balance chart worked out for any particular engine. For example, take the power balance chart of a four-cylinder engine, as shown in Fig. 18. If the order in which the suction strokes, the exhaust strokes, or the compression strokes occur is taken the same firing order results.

CHAPTER V

COOLING SYSTEMS

As previously shown the internal combustion engine is a machine for transforming heat into mechanical energy. As the heat increases a greater expansion of the gases results and more power is developed. However, there are certain limitations to the degree of heat that can be maintained in the engine and if the temperature were allowed to rise above a certain limit the degree attained would cause mechanical troubles. The intense heat would cause the cylinder to be scored, the valves to warp, and the lubricant to be burned up causing the piston and bearings to bind. It would also cause the incoming charge to become expanded and thereby cause a rarefied mixture. In addition to these things the spark plugs would crack and the temper would be taken out of the valve springs. From this it can readily be seen that some method of cooling the engine must be adopted.

As shown in the second chapter a considerable amount of heat is lost in cooling but this cannot be materially reduced for the tempera- ture of combustion far exceeds the temperature at which the engine ^^^^^^^^m could operate. The duty of the cooling system is to keep the en- gine from attaining a tempera- ture which would stop its opera- tion and is not to keep the engine cool, for in so doing it would increase the cooling losses and lower the efficiency. It is a misinterpreted idea in many cases that the cooling system is to keep the engine very cool. It has been found in testing en- gines that they operate best when the water, leaving the water jacket, is over 160° but well under the boiling point. There are two general systems of engine cooling in common use. First, by air which cools the engine by direct radiation. Second, by water which cools the engine and is subsequently cooled by air.

34

Fig. 24 — Air-Cooled Cylinder

COOLING SYSTEMS 35

There are certain things which must be taken into consideration when cooling an engine by air. First, the cooling depends upon the amount of surface presented to the air. Therefore in motor cycles the effective outer surfaces of the cylinders are increased by the addition of fins or flanges cast on them and presenting a greater surface for cooling as shown in Fig. 24. Second, the cooling depends upon the amount of air passing over the cooling surface. As the amount of air passing over this surface is increased the cooling will be proportionately increased. On motor-cycles where there is no fan to keep the air in circulation it is essential that the motor-cycle be kept in motion as long as the engine is running, otherwise over- heating of the engine will result. Third, the cooling depends upon the temperature of the air passing over the cooling surface. This results in the engine being kept cooler in cold weather than in warm weather. The rear cylinder of the engine will not be cooled the same amount as the front cylinder. This is because the air becomes heated after passing the front cylinder, therefore, it cannot have an equal cooling effect on the rear cylinder.

With twin-cylinder motor-cycles difficulty will often be experi- enced with the rear cylinder due to this unequal cooling. There is more probability of carbon being formed in this cylinder which will lead to ignition troubles and engine troubles in general. In case a miss in one cylinder is noted it is best to look first for the trouble in the rear cylinder.

Because of its simplicity and light weight the air-cooled engine is particularly suitable for motor-cycle engines. The small size of the engine together with its exposed cylinders insures proper cooling and makes this type of cooling ideal for the motor-cycle.

When water is employed in cooling it must circulate through jackets around the combustion chamber and be kept in motion either by heat or forced circulation. The water is heated by the cylinders and then passes to the radiator where it is cooled by air being drawn through the radiator by a fan. There are three general systems of water cooling in use: the Thermo Syphon, the Force System, and Thermostatic Controlled.

The THERMO-SYPHON COOLING SYSTEM, shown in Fig. 25, is a typical construction. The water enters the cylinder jacket at "A" and upon becoming heated by the combustion within the engine, rises and enters the pipe "B" and passes to the radiator "C" where it is brought into contact with a large cooling surface "D." When water is cooled it becomes heavier and therefore sinks to the bottom of the cooling system. As the water is heated in the cylinder jacket and rises to the top it must be replaced by cool

36

MOTOR VEHICLES AND THEIR ENGINES

water and therefore the water from the lower pipe "A" enters the water jacket.

Fig. 25 — Thermo-Syphon Cooling System

It can readily be seen that this circulation is proportional to the heat and as the heat increases the circulation becomes faster. This is an ideal condition for keeping the engine at the proper tempera- ture. Since there could be no circulation when the engine is cold the possibility of cold water continuously passing through the water jacket is eliminated, a condition which would keep the engine at a temperature less than should be maintained for proper efficiency. As the circulation depends solely upon the heat it is not positive and a slight amount of foreign matter obstructing the passages would interfere with the circulation. Another objection to the Thermo- Syphon system is that in case enough water evaporates, the water level will fall below the pipe entering the radiator, the circulation will stop, and the engine overheat. To prevent this it is essential that the radiator be kept completely filled. In extremely cold weather freezing of the lower pipe may occur after the car has been on the road for a short time. This is due to the circulation being very sluggish in cold weather and the last point reached by the water warmed in the cylinders is the lower pipe. As soon as freezing takes place circulation stops and overheating results. The water in the jackets is heated and rises to the top but cannot pass down through

COOLING SYSTEMS

37

the radiator to be cooled. This trouble arises from not running the engine sufficiently to warm up all the water in the cooling system before starting out.

• Radiator Cap

• Filler Neck

• Top Tank •Splash Plate

• Overflow Tube

• Radiator Tubes Rad Inlet Conn

•Cyl. Outlet Hose Hose Clip

Cyl.nder Head Cylinder Casting Cylinder Inlet Connecuon

Lower Hose-.

Lower Hose Clip

Rad Outlet Conn V Quilei Cona Pipe

Dram Cock Fan Assb.

Lower Tank

Fig. 26 — Ford Cooling System

Fig. 26 shows a typical Thermo-Syphon system. The arrows indicate the course of the water through the water passages. This is one of the few American motor cars that retains the Thermo- Syphon cooling system.

THE FORCE COOLING SYSTEM shown in Fig. 27 is a typical construction. In this system water leaves the cylinder jackets through the pipe from the cylinder head and enters the radiator through the radiator inlet pipe. The water passes through the radia- tor where it is cooled by the air drawn through the radiator. From the radiator the water passes through the radiator outlet pipe and through the pump to the cylinder jackets.

While the engine is in operation the pump, being geared to it, causes the water to circulate so that slight obstructions will not clog up the system. In case the radiator is not completely filled the pump will still circulate the water causing it to overflow from the radiator inlet pipe. The only part of the system in which there will be no water will be the upper section of the radiator. The level in

38 MOTOR VEHICLES AND THEIR ENGINES

the radiator will depend upon the quantity of water in the system. If there is too little water the level will be so low that the efficiency of the radiator in cooling the water will be reduced to such an extent that overheating will often result. Since the water is always in circulation when the engine is running there is little possibility of freezing.

WAT'SR. HOSE

Fig. 2? — Dodge Cooling System,

As the pump is positively geared to the engine the circulation will be proportional to its speed and for a given speed the amount of cooling will vary according to the temperature of the air. On a cold day as much water is passed through the water jackets as on a warm day, but the temperature of the water is considerably lower and the engine is kept too cool resulting in considerable loss of efficiency. This is particularly noticeable when starting an engine in cold weather for it causes misfiring due to the cold water being circulated through the water jackets. To prevent excessive cooling of the engine, which reduces its efficiency, the fan may be disconnected thereby reducing the cooling power of the radiator. A more satis- factory method is to cover part of the radiator's cooling surface. The best results are obtained when an adjustable device or shutter is used.

Natural circulation is of practically no assistance in the Force Cooling System; it depends entirely upon the pump for circulation. This permits the use of smaller water jackets and piping and as it is the practice to construct the engine as light as possible, these are made as small as practicable. In case any difficulties arise which stop the operation of the pump, natural circulation cannot be de-

COOLING SYSTEMS

pended upon to sufficiently cool the engine as it does in the Thermo- Syphon System, where large water jackets and pipes are used.

THE THERMOSTATIC CONTROLLED COOLING SYSTEM. — A Thermostatic device is introduced in this system in order to overcome the difficulties which arise in the Forced Cooling System when cooled water is circulated through the water jackets. The temperature of the liquid circulated by the pump is under Ther- mostatic control. The purpose of this is to permit water circulating through the water jackets of the cylinders and carburetor intake manifold to warm up to the temperature at which the engine operates best, very soon after the engine is started and to prevent the tem- perature dropping below this point while the engine is running. To explain the operation of the Thermostatic Controlled Cooling System, those used on the Cadillac and Packard will be described.

On the Cadillac the circulation through each cylinder block is independent of that through the other, two separate pumps being provided. Two centrifugal pumps are located at the front end of the crank case, on each side, and are driven from the crank shaft through helical gears. A housing containing a Sylphon Thermostat

and a valve controlled by the

Thermostat are located on the cover of each water pump. The Thermostat "A" (Fig. 28) is accordion shaped. It contains a liquid which is converted into gas when heated. The resulting pressure elongates the Thermostat, forcing the valve "B" from its seat. A drop in temperature changes the gas to a liquid, reducing the pressure in the Thermostat and allowing it to contract, bringing the valve "B" back to its seat.

When the temperature of the water in the water jackets on the cylinders and intake manifold is below a predeter- mined point the valve "B" is held tightly closed by the Ther- mostat which prevents water being drawn from the radiator. When the temperature of the water tends to rise above the predetermined point the valve "B" is forced open by the Thermostat, permitting

Fig. 28 — Thermostat Regulator on Cadillac

40

MOTOR VEHICLES AND THEIR ENGINES

the water pump "P" to draw water from the radiator. Provision is made for forcing the valves operated by the Thermostat from their seats. This is necessary to drain the radiator.

S F K P H

Fig. 29 — Cadillac Cooling System

When the engine is first started and is cold the valves operated by the Thermostats are held tightly on their seats. This prevents the water pumps from drawing water from the radiator. Under these conditions the water is circulated as follows: From the water pump "P," (Fig. 28 and 29) through the hose "F" to the water jackets on the cylinders, from the water jackets on the cylinders some of the water returns to the pump "P" through the hose "C" and the Thermostat housing "E," and the remainder is carried by a small pipe "N" to the water jacket around the intake manifold and from the intake manifold to the pump "P" through the pipe "D" and the Thermostat housing "E."

After the engine has become warm and the valves between the pumps and radiator have been forced from their seats by the Thermo- stats the circulation is as follows: Water is drawn from the radiator through the hose "G" and forced to the water jackets on the cylinders through the hose "F," from the water jackets the water returns to

COOLING SYSTEMS 41

the radiator through the hose "M" connecting the cylinder block and radiator. Water is still forced to the water jackets on the intake manifold through the small pipe "N" and from the intake manifold to the pump "P" through the pipe "D" and the Thermostat housing "E." Some of the water still flows back to the pump through the hose "C" and the Thermostat housing "E."

As the temperature of the water returning to the pump through the pipe "D," hose "C," and Thermostat housing "E" rises or falls, the Thermostat expands or contracts, opening or closing the valve, thereby admitting a larger or smaller amount of cooled water from the radiator. A condenser, the purpose of which is to prevent the loss of the cooling medium by evaporation particularly when an alcohol solution is used, is attached to the right-hand side of the frame just beneath the front floor boards. A pipe "S" (Fig. 29) connected to the overflow tube of the radiator leads to the condenser.

The condenser acts in this manner. The vapor rising from the heated liquid in the radiator passes through the overflow tube to the condenser. As it passes into the liquid in the condenser the vapor is condensed. When the engine has stopped the cooling of the radiator and its contents results in the contraction and condensation of the vapor left in the upper part of the radiator. The partial vacuum thus caused allows the atmospheric pressure in the condenser to force condensed vapor back into the radiator. The proper operation of the condenser requires an air-tight joint at the radiator filler cap. To make it possible to screw down and tighten the cap without injury to the rubber gasket, two metal washers are interposed between the head of the cap and the gasket. It is important that nothing be installed on the radiator filler cap which might cause a leak at the cap or which might make necessary the elimination of the steel washers or the cutting of a hole through the rubber gasket.

In the Thermostatic Controlled Cooling System as used on the Packard (Fig. 30) there are two paths through which the water may circulate. The water is forced by the pump through the cylinder water inlet manifold, thence through the water jackets, and out through the pipe at the top of the cylinder block. From here it has two paths through which it may return to the pump. It may pass through the bypass manifold directly to the pump or through the radiator returning to the pump by the lower pipe.

The path which the water takes is regulated by the Thermostat which operates a valve in the pipe leading to the radiator. The operation of the Thermostat is identical with that on the Cadillac, the only difference being its location.

COOLING SYSTEMS

43

The great advantage of a Thermostatic Controlled Cooling System is its efficient operation in cold weather in preventing cold water being circulated through the water jackets and cooling the engine below an efficient running temperature. There is little possi- bility of the radiator freezing because the length of time required to heat the small quantity of water in the jackets is very short. This results in sending a quantity of heated water almost immediately into the radiator. The Thermostat will gradually permit the heating of the water in the entire system always maintaining the water in the jackets at approximately the same temperature.

Fig. 31 — Phantom View of Centrifugal Pump

PUMPS.— There are several constructions of pumps used for water circulation, the most common of these being the centrifugal and gear types. omer

In the centrifugal type (Fig. 31) the water enters at the center of the pump and is caught by the rotating blades and thrown to the out- side by centrifugal force. .' The casing limits its out- \ ward motion, but allows \ the blades to impel it in circular motion, the pres- sure against the casing increasing until the out- let pipe is reached. Here the resistance to its out- Fig. 32— Gear Pump

44

MOTOR VEHICLES AND THEIR ENGINES

ward motion is removed and the stored-up energy forces the water through the discharge pipe to the water jackets.

In the gear pump (Fig. 32) the water takes the path indicated by the arrows. The gear teeth pick up the water and carry it around in the spaces between the teeth, the pump casing making a tight joint. The teeth of the two gears meshing at the center prevent any water being carried down between them, hence a steady stream of water will be forced out the discharge pipe.

RADIATORS. — The purpose of a radiator is to present a large amount of cooling surface to the air In order to accomplish this

Fig. 33 — Tubular Radiator Sections

there are many constructions varying in design in accordance with the manufacturer's ideas. All radiators may be classed as either

tubular or cellular. The so- called honeycomb radiator may ,v,,?: be either tubular or cellular (though generally the latter) and <"- gets its name from its appearance. The tubular radiator is one in which the upper and lower tanks are connected by a series of tubes through which the water must pass. The tubes may be arranged vertically or in a zig-zag fashion which materially in- creases the cooling surface. Fig. Z^Tubular Radiator In FJg 33 ^.^ ^^

constructions are shown, that in the lower left-hand corner being a honeycomb type.

COOLING SYSTEMS

45

In Fig. 34 a straight vertical tube type of radiator is shown and is typical of the construction used for trucks. To increase the radiating surface fins are employed on the tubes.

The cellular radiator (Fig. 35) is composed of a large number of individual air cells which are surrounded by water and the course of the water through the radiator is not confined to any definite vertical

Fig. 35 — Cellular Radiator Sections

or angular course. Because of its appearance the cellular type is usually known as a "honeycomb" radiator.

Since the water passes through all of the tubes of a tubular radiator, if one tube becomes clogged the cooling effect of the entire tube is lost. In the cellular construction the clogging of any passage results in a loss of but a very small part of the total cooling surface as compared to the loss of a whole tube in the tubular type. For this reason the cellular or commonly called " honeycomb " radiator is more efficient but is more expensive to construct.

FANS. — In order to cool the water sufficiently a fan driven by a belt or chain from the engine is placed back of the radiator so that in its operation it will draw air through the radiator. In many con- structions of radiators the mere motion of the car could not force sufficient air through the radiator but, by placing a fan behind it, sufficient air will be drawn through for cooling purposes. It is a misinterpreted idea that a fan is used to cool the engine, its function being solely to assist in cooling the water in the radiator. In some constructions it may assist slightly in cooling the engine.

The fan bracket is so constructed that the tension on the belt is adjustable. At all times the belt should be under sufficient tension to prevent slippage. Fans require but little power and usually run at a speed two or three times as great as that of the crank shaft and are mounted on ball-bearings to reduce friction as much as possible.

46 MOTOR VEHICLES AND THEIR ENGINES

ANTI-FREEZING MIXTURES.— In order to prevent the water in the cooling system from freezing in extremely cold weather when the engine is not in operation there is provided at the bottom of the radiator, at the lowest points in the water jackets, and at the pump, drain cocks through which the water can be removed. Water in freezing expands and if confined in the cooling system would cause the water jackets, pipes, or radiator to break. As an assurance in freezing weather that the cooling system of a car has been drained and as an indication that it must be filled before operating the car, a card marked DRAINED in black letters about three inches high should be conspicuously displayed. This is usually done by sus- pending the card across the radiator from the filler cap. As it is often found undesirable to remove the water from the cooling system fluids with very low freezing points are often employed. These are called anti-freezing mixtures. The ideal requirements for an anti-freezing mixture are as follows:

1. It should cause no harmful effect to any part of the cooling system with which it comes in contact.

2. It should be easily dissolved or combined with water.

3. It should be reasonably cheap.

4. It should not waste by vaporization, that is, its boiling point should be as high as that of water.

5. It should not deposit any foreign matter in the jackets or pipes.

The materials which are most commonly used are alcohol, mix- tures of alcohol and glycerine, kerosene oil, and calcium chloride. The most common of these are solutions of alcohol and water in the following proportions:

WATER

80% 70% 60%

The above table is based on the use of denatured alcohol but if wood alcohol is used, slightly lower temperatures can be reached with the same proportions of alcohol and water. In these solutions, the alcohol being more volatile than water, will evaporate making it necessary to continually add more alcohol. The use of this solution is very unsatisfactory because the only method of being positive that the alcohol is present is by measuring the specific gravity of the solution.

There are certain solutions of glycerine, alcohol, and water which are more stable because the glycerine holds the alcohol in solution.

ALCOHOL

SPEC. GRAY.

FREEZING POINT

20%

.975

14°

30%

.964

- 1°

40%

.954

-20°

COOLING SYSTEMS 47

The following table shows the percentage of each and the freezing points of the solutions :

ALCOHOL GLYCERINE WATER FREEZING POINT

12% 12% 76% 10°

15% 15% 70% - 5°

17% 17% 66% -15°

These solutions are very satisfactory as they are dependable, but it often happens that the glycerine will gum up the radiator and stop the circulation of the water through some section thus reducing the cooling.

Calcium Chloride or alkali solutions are often recommended, their freezing points being very low. The great objection to the use of these is that they form a scale in the water jackets and radiator which in time interferes with the circulation. When Calcium Chloride is used it must be chemically pure as the commercial chloride of lime sets up electrolytic action. The following solutions are used :

CALCIUM CHLORIDE WATER SPEC. GRAY. FREEZING POINT

20% 80% 1.119 0°

22% 78% 1.200 - 9°

24% 76% 1.219 -18°

Kerosene has the advantage of a high boiling point so that it does not evaporate readily but it has the disadvantage of not making a good mixture with water and will not absorb heat as rapidly. Kero- sene should not be used where there is any rubber in the system for it attacks the rubber hose and gaskets and causes them to deteriorate rapidly.

Whenever an anti-freezing mixture is used it is essential that it be removed from the cooling system as soon as the weather moderates. If this is not done the engine will overheat.

If the water in the cooling system should freeze through neglect of ordinary precaution do not attempt to thaw it by starting the engine, but thaw by putting the car in a warm place or by draining the system and then adding hot water. It has been stated that solutions of Calcium Chloride deposit a scale in the water jackets and radiator and therefore should not be used. There are many places in which the drinking water contains a considerable amount of lime which will cause the same result. To prevent scale it is always best to fill the cooling system with rain water.

CHAPTER VI

FUEL FEED SYSTEMS

Provision must be made on motor-propelled vehicles for storing gasoline and supplying it to the carburetor. There are three systems in common use for supplying liquid fuel to the carburetor from the storage tank, the Gravity System, the Force Feed System, and the Vacuum System.

GRAVITY SYSTEM.— In the gravity fuel feed system the storage tank must be placed above the carburetor so that the gasoline will flow from it to the carburetor by gravity. A typical system of this kind is shown in Fig. 36. It is very simple and has but a few parts. The storage tank has a filler cap in the top with an air vent through it and a gasoline outlet at the bottom which leads to a sediment well

r.ASOLINE TAKK COVCR SHUT OFF. VALVE.

AUXILIARY AIR ADJUSTMENT

THROTTLE LEVER .BELL-CRANK

OPERATING A ;o- IN TAKE VALVE

ruOAT-CHAMBER CAP. • LOW SPEED

ADJUSTMENT

GASOLINE »MD OPE

Fig. 36 — Gravity Fuel Feed System

and drain plug. The feed pipe to the carburetor takes off from the top of this well and is as straight and short as possible. A stop cock for shutting off the supply of gasoline from the tank is provided in the outlet underneath the tank or a needle valve is used inside the tank which can be controlled from the top. Automatic gauges are sometimes provided on the storage tank to show the amount of fuel in the tank.

Because of the simplicity of construction they are not apt to get out of order. On the other hand they have several drawbacks. The pressure varies with the relative height of tank and carburetor and since this is usually not very great the resulting pressure will be low. When ascending or descending grades the relative height of tank and carburetor will change which correspondingly varies the pressure. Since the tank must be above the carburetor for this

48

FUEL FEED SYSTEMS 49

system to be operative its location is very limited and it generally has to be placed at some point not readily accessible. This fact also makes it hard to shut off the supply of gasoline and in case fire occurs at the carburetor. The result may be serious if the supply of gasoline is not immediately shut off.

PRESSURE SYSTEM.— When the pressure fuel feed system is employed the storage tank may be placed at the most convenient and accessible point on the machine usually at the extreme rear of the chassis. When installed in this manner it is necessary to force gasoline out of the tank by air pressure since the gasoline tank is lower than the carburetor. Pressure is maintained by a small air pump automatically controlled and driven by the engine. An auxiliary hand pump gives enough initial pressure to force gasoline to the carburetor for starting. A safety valve in the pressure system prevents the pressure from rising beyond a safe limit. The tank must be airtight and the filler cap screwed tight with a wrench to hold the

Fig. 37 — Pressure Fuel Feed System

pressure. A gasoline gauge is provided to show how much gasoline the tank contains. Two pipes run from the tank, one being the pressure line and the other the gasoline line (Fig. 37). The gasoline line runs from the lowest point in the tank directly to the carburetor. The pressure line is connected to both the engine driven pump and the hand pump. The hand pump is shut off by means of a valve at its lower end when not in use. A pressure gauge may be attached to this line near the hand pump to show the pressure in the system at all times. Some systems have the pressure gauge attached to the gasoline line.

Since a constant pressure is maintained in the tank at all times the gasoline is fed uniformly to the carburetor and its flow is inde- pendent of the relative position of tank and carburetor. In addition to this the location of the tank is not limited, permitting it to be

50

FUEL FEED SYSTEMS 51

o*

placed in an accessible position where gasoline may be put in with the greatest facility. Should fire occur at the carburetor the supply of gasoline can immediately be shut off at the dash by turning the cock at the hand pump so that the pressure in the system can escape to the air. Trouble may be experienced in this system with leaks in the various pipes, valves, or filler cap and the pumps must be in proper working order for constant operation. In addition the pressure is liable to interfere with the operation of the carburetor float and prevent the needle valve from seating properly. However, the pressure feed system has been so highly perfected that few mechanical diffi- culties are apt to be experienced.

VACUUM SYSTEM.— In this system the gasoline is drawn from a supply tank in the rear of the car by suction to a small auxiliary vacuum tank near the engine from which it flows by gravity to the carburetor. The vacuum tank is installed under the hood and con- nected by tubing to the intake manifold, gasoline storage tank, and carburetor (Fig. 38). The suction created by the pistons on their outward strokes in the engine causes a suction in the vacuum tank through the connection to the intake manifold. This draws gasoline from the main supply tank into the vacuum tank through the tubing from the gasoline supply tank.

The Stewart Vacuum Gasoline Tank consists of two chambers. The upper is the filling chamber and the lower is the emptying chamber. Between these two chambers is a partition in which is placed a valve. The suction of the pistons on the intake stroke creates a vacuum in the upper chamber and this vacuum closes the valve between the two chambers and also sucks or pumps up the gasoline from the main supply tank into this upper chamber. As the gasoline flows into this upper chamber it raises a float. When the float has risen to a certain point, it operates a valve which shuts off the suction and at the same time opens an air valve. This admission of outside air releases the vacuum causing the valve leading into the lower chamber to open, through which the gasoline immediately commences to flow into the lower or emptying chamber. This lower chamber is always open to the outside air so that nothing can ever prevent the gasoline in it from feeding through its connection to the carburetor in an uninterrupted flow.

DESCRIPTION OF STEWART VACUUM TANK

"A" is the suction valve for opening and closing the connection to the manifold and through which a vacuum is extended from the engine manifold to the gasoline tank,

AIR'

FROM

GASOLINE SUPPLY TANK

TO CARBU- RETOR

Fig. 39 — Stewart Vacuum Tank

52

FUEL FEED SYSTEMS 53

"B " is the atmospheric valve and permits or prevents atmospheric pressure in the upper chamber. When the suction valve "A" is open and the suction is drawing gasoline from the main reservoir this atmospheric valve "B" is closed.

"C" is the pipe connecting the tank to manifold of the engine.

"D" is the pipe connecting the vacuum tank to main gasoline supply tank.

"E" is the lever to which the two coil springs "S" are attached. This lever is operated by the movement of the float "G."

"F" is a short lever which is operated by the lever "E" and which in turn operates the valves "A" and "B."

"G" is the float.

"H" is the flapper valve in the outlet "T" (Fig. 39). This flapper valve is held closed by the action of the suction whenever the valve "A" is open, but it opens when the float valve has closed the vacuum valve "A" and opened the atmospheric valve "B."

"J" is a plug in the bottom of the tank which can be removed for draining or cleaning the tank. This plug can be replaced with a pet cock to be used for drawing off gasoline for priming or cleaning purposes.

"K" is the line to the carburetor extended on inside of the tank to form a pocket for trapping water and sediment.

"L" is the channel space between the inner and outer shells and connects with the air vent "R," thus maintaining an atmospheric pres- sure in lower chamber at all times. This insures an even flow of gasoline to the carburetor.

"R" is an air vent over the atmospheric valve. The effect of this is the same as if the whole tank were elevated and is for the pur- pose of preventing an overflow of gasoline if the storage tank became higher than the vacuum tank. Through this tube also the lower or reservoir chamber is continually open to atmospheric pressure so that the flow of gasoline from this lower chamber to the carburetor is always an uninterrupted flow. This outlet is located at the bottom of the float reservoir in which is the flapper valve "H."

The simple durable construction used in the manufacture of the Stewart Vacuum Tank makes it unlikely that it will ever be neces- sary to make internal repairs. However, some of the following troubles may possibly be experienced. The vent tube may overflow and if it does this regularly the trouble may be:

1. The air hole in main gasoline tank filler cap may be too small or may be stopped up.

2. Vacuum tank may not be placed high enough above the carburetor.

54 MOTOR VEHICLES AND THEIR ENGINES

If faulty feed is due to the vacuum system it may result from one of the following causes:

1. Gasoline strainer may be clogged and should be examined first if the tank fails to operate.

2. The float may leak allowing gasoline to be drawn into the mani- fold which will choke down the engine.

3. Flapper valve may not seat properly.

4. Manifold connection may be loose allowing air to be drawn into it.

5. Tubing may have become stopped up.

This system supplies gasoline at a constant pressure but low enough not to interfere with the action of the carburetor float. This system does not limit the location of the supply tank but eliminates the trouble giving pumps and valves of the pressure system and permits the final supply of gasoline to the carburetor by gravity.

CARE OF GASOLINE. — Gasoline being a volatile liquid is very dangerous if not properly handled but is quite safe if the proper precautions are taken. It should never be exposed in a closed room as it will evaporate, mixing with air and forming an explosive gas. Open lights should never be used where gasoline vapor is apt to be encountered. When it is necessary to handle gasoline at night in the open an electric light should be used and under no circumstances should a flame be brought near the gasoline. When an open flame is used at some distance from gasoline, it should always be placed above the gasoline. Gasoline should be stored in an underground tank or in an air-tight container in a separate building used especially for that purpose.

In putting out a gasoline fire, water should never be used as the gasoline, being lighter than water, floats on it, resulting in spreading the fire. The only successful method of extinguishing a gasoline fire is to smother it with sand, sawdust, or a blanket or by the use of a chemical fire extinguisher. Each piece of motor equipment should be provided with a small chemical extinguisher for this purpose.

CHAPTER VII

FUELS

The crude oils from which gasoline is derived occur in various parts of the world and manifest a variety of properties. Thus the "paraffine base," Pennsylvania and Ohio oils yield 60 to 70 percent of kerosene and lubricating oils, while the "asphaltum base," Cali- fornia, Oklahoma, or Texas oil, furnishes practically nothing of either of these products. It is much heavier than Pennsylvania oil, and Mexican oil is usually still heavier. Crude oils having an asphaltum base are heavy and dark-colored and when distilled down leave a black tarry residue. If a crude oil has a paraffine base it is lighter in weight and color, and the residue after distillation yields (by pressure and refrigeration) the white paraffine wax. Either kind of crude oil will yield good gasoline. A large proportion of the world's supply of crude petroleum comes from American wells. These variations are indicated by the density, which varies from a maximum of 50° with Pennsylvania crude down to 12° or less with California crude. The lower the density, the less is the proportion of gasoline obtainable from the crude oil.

The density of liquids lighter than water (like fuel oils and their products) is indicated by

140 specific gravity =

where B is the hydrometer reading. The specific gravity is the weight of the liquid as compared with the weight of an equal bulk of water. Hence water would give an hydrometer reading of 10°. Water weighs 8^ Ibs. per gallon at normal temperature.

Crude oils are too heavy and viscious for use as fuels in internal combustion engines without special preparatory treatment. They require heating and may liberate poisonous or explosive gases which are heavier than air. They contain, as impurities, free carbon, sulphur, silt, and moisture, in widely varying proportions.

When crude oil is subjected to moderate heat those of its con- stituents which have low^boiling points are boiled off. By condensing their vapors, highly inflammable gasoline is obtained. After this a somewhat higher temperature may be applied and lower grade gasoline collected in a separate condenser. By successive increases

55

56

MOTOR VEHICLES AND THEIR ENGINES

GAS61WC. B£MZ/*/C, AW

of temperature, with separa- tion of products condensed, a considerable series of products is derived.

It would be commercially inadmissible to treat crude oil with a view to deriving gaso- line only. This process is called "fractional distillation," and is the basis of petroleum refining. As the temperature of distillation increases, the products become lighter (hav- ing a higher hydrometer read- ing and less fluid and inflammable. Fig. 40 shows the composition of a sample of American crude oil.

Fig. 40 — Composition of Crude Oil

AVERAGE FRACTIOXATION OF CRUDE PETROLEUMS (ROBINSON)

AMERICAN OIL

CONSTITUENT

PERCENT. OBTAINED

BOILING POINT, DEG. FAHR.

HYDROMETER READING, DEG.

Gasoline

0-10

32-265

58-107

Kerosene

12-55

300-700

44-49

Fuel oil (gas oil)

variable

35

Lubri eating oil

17^

22-28

Paraffin and residue

2-10

RUSSIAN OIL

Gasoline

5-16

53-63

Kerosene

40-52

33-41

Lubricating oil

3-40

22-31

Residue (fuel oil) ... .

10-15

17-25

The boiling point of any liquid varies according to the pressure to which it is subjected. If the boiling temperature at atmospheric pressure is less than the resisting temperature, the liquid will vaporize until a pressure is created equal to that at which boiling occurs at the existing temperature. The lighter gasolines therefore are always boiling off from the crude oils which contain them. Loss and danger can be avoided only by confining such oils.

FUELS

57

PRESSURES AND BOILING POINTS

Boiling Point, Deg. Fahr

70

80

90

100

110

120

140

Pressure, f Ordinary gasoline inches I Kerosene, poor*

8.9 1.0

10.0 1.2

11.8 1.4

13.8 1.5

16.4 1.6

19.6 1.8

2^3

of ordinary

0.6

0.7

0.8

0.9

1.1

1.3

1.7

Mercury [ water white. . .

0.6

0.6

0.6

0.7

0.7

0.8

1.0

*Poor for use as an iUuminant, because volatile and therefore unsafe. The most dangerous illuminating kerosenes, are, however, the best as fuels for internal combustion engines.

To convert pressure in inches of mercury to Ib. per sq. in., mul- tiply by 0.49. Thus, if gasoline is vaporized at 120° F. its vapor pressure is 9.6 Ib. per sq. in. The lower the pressure, the lower the temperature at which vaporization occurs. Suction, therefore, facilitates carburetion.

The proportions of the various products obtainable from re- fining any particular crude oil cannot be changed by the refiner. In getting 5 percent of gasoline, for example, he is compelled to accept 40 percent of kerosene, say. If the demand for kerosene is slight, while the demand for gasoline is brisk, he may have to sell the former at a loss and protect himself by charging an excessive price for gasoline. There is no such thing as "cost of production11 chargeable against any one of the products. When any one is cheap, others must be dear. If gasoline is cheap at any time it is because there is relatively a greater demand for other products. About 1903 kerosene was cheaper than gasoline in some sections. Recently it has been twice as costly.

The average gasoline consists mainly of carbon and hydrogen: From 83J^ to 85 parts of the former to 15 to 15 J^ of the latter by weight. Good commercial gasoline should show an hydrometer read- ing between 67° and 73°. Grades down to 50° are sometimes offered. They are, of course, not true gasoline, but may be used in warm weather without difficulty. This density is about the same as that of some of the best samples of Pennsylvania crude oil. At 68° the specific gravity is 140 -^ 198 = 0.71. Since water weighs 8.33 Ib. per gal., this gasoline weighs 0.71X8.33 = 5.91 Ib. per gal. Petroleum products are always sold by bulk; the gallon or the 42-gal. barrel. It would be fairer if they were sold by weight.

The weight per measured gallon is an exact indication of the density. If w = weight per gallon, B = hydrometer density, then

1 -t r>rj

B = - -130. Thus if the weight per gallon is 5.835 Ib., B = 70°. It will be noted that some slight amounts of the lighter gasolines

58 MOTOR VEHICLES AND THEIR ENGINES

are obtained by distillation at temperatures as low as 32° F.; i.e., without any heat at all. In fact, as much as IK percent of some American crude oils will distil off at temperatures below 150° F. These products are highly inflammable and dangerous. It is not always possible to market them. By blending them with rather light kerosene a substance is produced which may be regarded as gasoline, for it has the density of the latter. It has different properties, how- ever, notably with respect to igniting point and vapor pressure.

Gasoline may be produced from natural gas by the combined effects of pressure and cooling. Improved methods of distillation (Burton and Rittman processes,* etc.) increase the gasoline yield from crude oil, but usually at the cost of some impairment to quality.

Average gasoline must be supplied with air in the ratio 15 to 1 by weight for complete combustion. This means that 1 Ib. of fuel requires 200 cu. ft. of air at 62° F. Gasoline vapor weighs 0.24 Ib. per cu. ft. at atmospheric pressure and 32° F., or is about three times as heavy as air. About 50 cu. ft. of air are required to make a perfect combustible mixture with 1 cu. ft. of gasoline vapor. These ratios may be considerably varied without preventing ignition, but if varied the power and efficiency are influenced unfavorably. According to Lucke, limits are as follows:

RATIO OP GASOLINE VAPOR TO TOTAL MIXTURE, BY VOLUME

86° Gasoline " 0.0154 to 0.0476

71° Gasoline 0.0154 to 0.0476

65° Gasoline 0.0131 to 0.0476

If these limits are passed, the mixture will not ignite explosively (at atmospheric pressure, by electric spark). As has been shown, the best value is about & or 0.02. A rich mixture causes failure to ignite less promptly than does a weak mixture.

The heat value of a fuel is expressed in British thermal units (B. t, u.). One B. t. u. is the quantity of heat necessary to raise the temperature of 1 Ib. of water 1° F. It is equivalent to 778 ft. Ib. of mechanical energy. Since 1 horse power = 33,000 ft. Ib. per min., it is also equal to 33,000 -f- 778 = 42.42 B. t. u. per min. Average gasoline contains from 19000 to 21000 B. t. u. per Ib. In general, for all petroleum distillates,

B. t. u. per lb. = 18650+40 (B-10). Thus for 68 gasoline, B. t. u. per lb. = 20970. The lighter the dis-

*The Burton process involves the obtaining of gasoline by redistillation of less volatile products under pressure. The Rittman process, developed by the United States Bureau of Mines, is similar, but the operation is conducted con- tinuously instead of in batches.

FUELS 59

tillate the higher the heat value. One horse power is 42.42 B. t. u. per min. or 42.42X60 = 2545 B. t. u. per hr. The gasoline con- sumption of a perfect engine would be 2545 -T- 20970 = 0.121 Ib. per hour per horse power. Actually it is four to seven times this or more, on account of the inefficiency of the engine. High compression — which follows low clearance — reduces the fuel consumption.

The fuel consumed per mile depends on the traction force exerted, the efficiency of engine and driving mechanism, and the speed. If p = average pressure in the cylinder during the power stroke, d = diameter of cylinder and n the number of cylinders, the total pressure continuously maintained in a four-cycle engine is P = ?rd2np. If the stroke is s and the engine makes r rev. per min., and if the efficiency from cylinder to wheels is e, the horse power exerted at the wheels if H = Pesr-J- 198000. If the gear ratio is g (engine speed divided by wheel speed) and the wheel diameter is D in., the speed of the truck is V = nDr ^- 1056 g. The tractive force is T = 375 H + V = 2 Pesg-r-7rD, which is practically independent of the engine speed. Take p = 70, d = 5, n = 4 : then P = 1375. Take s = 7, r = 700, e = 0.70. Then H = 23.8. Take g = 5, D = 34: then V=14.2 miles per hour, and T = 629 Ibs. When working at full traction, H is about nd2-j-2.5 and the fuel consumption about 0.7 H Ib. per hour.

If gasoline is used composed of 84 parts of carbon to 16 of hydro- gen, by weight, about 15.22 Ibs. of air will be the correct amount per Ib. of fuel. More air will give more power, but at a sacrifice of efficiency. Suppose the truck to make 5 miles per gallon of gasoline. If the liquid fuel were stretched out along the road in a pipe, the tube of fuel containing one gallon or 231 cubic inches would be 5 miles or 316800 inches long, and its diameter would be about %3 of an inch. A similar pipe full of air would contain 1130 cu. ft., or the diameter would be 2.8 inches. This illustrates the point that most of what goes into the cylinder under any condition is nothing but air.

Since 1 Ib. of gasoline produces about 200 cu. ft. of combustible mixture, the mixture contains about 20970 -T- 200 = 105 B. t. u. per cu. ft. This is reduced if the temperature is higher than 62° F., because 200 cu. ft. at 62° F. will occupy a larger volume at higher temperatures.

Efforts are constantly being made to find acceptable substitutes for gasoline. The most important substitutes may be grouped in three classes: Lower grade distillates, including kerosene; alcohol; and coal-distillation products, such as benzol. The study of sub- stitutes has until recently been carried on much more thoroughly in Europe than in this country, because there are no readily accessible supplies of gasoline from the commercial centers of the continent.

60

MOTOR VEHICLES AND THEIR ENGINES

KEROSENE has very nearly the same percentage composition as gasoline, but its density being greater, its heat value is less. It requires more air for combustion, and the heat value per cu. ft. of combustible mixture is less. The lower heat value is not an objection ; in fact, it is in one way an advantage. Low heat values mean a high igniting temperature. This permits of more compression without danger of pre-ignition, and high compression increases both power and efficiency. However, a high ignition temperature does itself introduce difficulties.

The essential objection to kerosene is the difficulty of vaporizing it. The table shows that its boiling point is 300° F. or more. Gas- oline may be vaporized either by pure evaporation in a slow current of warm air, or by spray-injection. Kerosene needs heat. This may be supplied externally, at the carburetor; or the fuel may be delivered to the cylinder in liquid form by a pump and vaporized by contact with a hot (un jacketed) cap or plate forming a part of the cylinder. This is the method of the Hornsby-Akroyd stationary engine, but the timing of ignition is uncertain, especially under variable loads. For motor cars, carburetor heating is more prom- ising.

Kerosene is not necessarily more apt to form carbon deposits. These will result from any blended fuel in which the free carbon of the heavier constituents has not been thoroughly filtered out, or from any fuel at all under appropriate conditions of carburation and cooling.

Alcohol as a fuel has had considerable attention. There are two kinds, methyl or wood alcohol, and ethyl or grain alcohol. The former contains half the carbon and two-thirds the hydrogen of the latter. It has only about three-fourths the heat value and requires less air for combustion. Unlike petroleum distillates, both of the alcohols contain oxygen. Commercial alcohols always contain water. This does not destroy their value as fuels. The following table shows the effect. The B. t. u. per Ib. are adjusted values, which

Percent of Alcohol in Mixture, by Weight

93 8

87 8

81 8

76 1

70 5

65 0

Specific Gravity

0.805

0 815

0 826

0 836

0 846

0 856

B. t. u. per Ib

10880

10080

9360

8630

7920

7200

are comparable among themselves, but not with those given for petroleum distillates. For the latter purpose, the heat value of pure ethyl alcohol may be taken at 12800 B. t. u. per Ib. Denatured alcohol is a mixture of pure ethjrl alcohol, 90 parts; water, 10 parts;

FUELS 61

methyl alcohol, 10 parts; and benzine, J/£ part; by volume. Alter- natively, the last two constituents may be replaced by methyl alcohol, 2 parts, and pyridin bases, Y^ part. Denaturing makes alcohol unfit for use in connection with beverages.

One cubic foot of, alcohol vapor requires 14J/£ cu. ft. of air for complete combustion. It will ignite when the air volume is any- where between 7 and 25 cu. ft. If the air supply is seriously deficient, the combustion products will contain acetic acid, which causes rusting and corrosion. The igniting temperature of alcohol vapor at atmospheric pressure is 950° F. The alcohols are intermediate between gasoline and kerosene in their readiness of vaporization, and methyl alcohol is particularly close to gasoline in its vaporizing properties. Moderate heating at the carburetor is required in cold weather. Higher compression is necessary than with gasoline, for the same power and efficiency, and the engine must be specially designed for such high compression. Tests have shown that where 70 Ibs. compression pressure was used for both fuels, the alcohol engine consumed 50 percent more fuel than that burning gasoline. By raising the compression of the former engine to 180 Ibs., its fuel consumption became the same as that of the gasoline engine: 0.10 gallon per hour per horse power. Unfortunately the present methods for distillation of alcohol from vegetable substances have not yet produced that fuel at a price competitive with that of gasoline.

Benzol is a by-product of the distillation of soft coal, for the manufacture of coal gas or coke. It appears both in the gas and in the liquid tar, and is derived only when by-products or retort ovens are used. It ignites at 970° F. at atmospheric pressure. Its specific gravity is 0.88 and its heat value about 18000 B. t. u. per Ib. About 13}/£ Ib. of air are required for combustion of 1 Ib. of benzol, or about

36 cu. ft. of air for 1 cu. ft. of benzoL Ignition is possible with 15 to

37 volumes of air, but weak mixtures are very uncertain. Benzol has been used in three ways. While somewhat less volatile than gasoline, it has been vaporized in an ordinary carburetor, after starting on gasoline. By adding benzol to alcohol there is less danger of corrosion from acetic acid formation. In Europe, a mixture of equal parts of benzol and alcohol has frequently been employed as a motor fuel. The mixture had a heat value of 14200 B. t. u. per Ib. Commercial benzol has been charged with excessive carbon formation, but so has commercial gasoline of the present day.

There seems to be little possibility of the direct use of crude oil, coal tar (a by-product from coal-gas distillation) or tar oil (by-pro- duct from tar distillation) in the cylinders of motor-car engines. Even in stationary engines of the hot-cap type they have been un-

62 MOTOR VEHICLES AND THEIR ENGINES

satisfactory. Extremely high compression and still higher fuel- injection pressures, usually complicated by an air blast, have thus far been necessary. The engines have been heavy and costly and in many instances unreliable. Kerosene is the most promising cheaper fuel, but the kerosene problem will not be solved until the starting problem, as well as the running problem, is solved. There seems to be no good ground for apprehension that the substitution of kerosene will leave us where we are now, as far as cost is concerned. The yield of kerosene is very much greater than that of high-grade gasoline. In fact, kerosene is simply low-grade gasoline. Circumstances are compelling the use of lower and lower grades, so that a gradual approximation to kerosene as fuel seems both the most probable and the easiest direction for progress. The necessary modifications of equipment have in a measure been already anticipated by such devices as water-jacketed and hot-air-jacketed carburetors, etc.

CHAPTER VIII

ELEMENTS OF CARBURETION

Pure gasoline vapor must be combined with oxygen in order to render it inflammable. The simplest manner of effecting this is to mix air with gasoline. When the correct proportions are obtained the oxygen supplied by the air will be sufficient to result in the com- plete combustion of the gasoline vapor without a surplus of either of the ingredients. This mixing is called carburetion and the air is said to be carbureted.

The carburetor is a metering device whose function is to blend mechanically a liquid fuel with a certain amount of air to produce as nearly a homogeneous mixture as possible and in such proportion as will result in as perfect an explosive mixture as can be obtained.

With a liquid fuel such as gasoline it is difficult to obtain this perfect mixture especially with low test gasoline. If it were possible to transform a liquid fuel into its vapor, the vapor would act as a gas and would mix easily with the air to form a homogeneous mixture. The carburetor should be so designed as to atomize the fuel and break it up into as small particles as possible so every minute particle of the fuel is surrounded by the correct proportion of air as it enters the inlet manifold of the engine. To facilitate the vaporization of these minute particles of fuel it is advisable to heat the air taken into the carburetor.

There is a range of proportions of air to vapor for a given fuel between which combustion will result. This range* extends from that proportion known as the UPPER LIMIT OF COMBUSTION to that known as the LOWER LIMIT OF COMBUSTION. The upper limit is reached when the ratio of air to vapor is a maximum at which combustion will take place, any further addition in air rendering the mixture non-combustible. The lower limit is reached when the ratio of air to vapor is a minimum at which combustion will take place, any decrease in air below this point producing a non- combustible mixture. It should be remembered that the limits of combustion are dependent upon the temperature and pressure.

The limits of combustion of gasoline (70° Sp. Gr.) can be taken approximately as follows: Lower limit, 7 parts air (by weight) to 1 part of gasoline; upper limit, 20 parts air to 1 part gasoline. Under given temperature and pressure the ratio at which a combustible

63

64 MOTOR VEHICLES AND THEIR ENGINES

mixture will burn depends upon the ratio of air to vapor. This rate of burning is known as the RATE OF FLAME PROPAGATION and it is desirable to obtain a mixture whose rate of flame propagation is a maximum because the expansion will depend upon the rapidity with which the entire mixture- is completely burned.

Rich mixtures have a greater proportion of fuel vapor and are slow burning and sluggish. They also cause carbon to be deposited in the combustion space because of their incomplete combustion. Mixtures that have too great a proportion of air are very erratic in their combustion. The mixture in the cylinders is often formed in layers and as each layer burns independently of the other the rate of burning is slow. The term LEAN MIXTURE is often used to desig- nate not only this type of mixture, but those which have not reached the upper limit. These mixtures have a high rate of flame propa- gation. When mixtures are too lean they cause misfiring of the engine and also cause back firing into the carburetor.

A carburetor must be constructed to maintain the proper pro- portions of gasoline and air under all conditions. To accomplish this several designs and principles have been evolved which will be discussed in the following chapters. Types of carburetors which are not commonly used will not be discussed because the principle upon which they are based has not proven satisfactory for motor vehicles.

Before taking up any of these types it is necessary to study the basic principles underlying carburetion. These will be most clearly understood when applied to a simple carburetor of the spray nozzle

type. The gasoline supply from the storage tank enters the float chamber "F" of the carburetor and as the gasoline level rises the float presses against the levers at the top of the float chamber (Fig. 41). These levers are pivoted so that their outer ends are raised by the float. Their inner ends working in a collar or recess, press the float needle valve downward into its seat. This shuts off the

Fig. 41— Simple Carburetor suPP!y of gasoline when the level

in the float chamber has reached

the proper height. The height at which this gasoline should be main-, tained is governed by the nozzle or jet "G." The level must stand approximately %§ below the top of this nozzle. The gasoline is fed

ELEMENTS OF CARBURETION 65

to the nozzle "G" from the float chamber through the pipe "E." The inlet valve being open when the piston moves outward in the cylinder on its suction stroke, air will be drawn through the carburetor, as indicated by the arrows in Fig. 41, passing the nozzle on its way to the cylinders. The suction created by the rush of air past the spray nozzle causes the gasoline to be delivered to the mixing chamber in a fine spray. Since the suction depends upon the velocity of the air passing the nozzle, a Venturi tube "X" is used.

A Venturi tube is a tube which is narrowed at the center so that the area through which the air must pass is considerably decreased. As the same amount of air must pass through every point in the tube its velocity will be greatest at the narrowest point. The more this area is reduced the greater will be the velocity of the air and the suction will be proportionally increased.

The sp^-ay nozzle should be located where the suction is greatest which is just above the narrowest part of the Venturi tube. The spray of gasoline from the nozzle and the air entering through the Venturi tube are mixed together in the mixing chamber, that portion of the tube immediately above the spray nozzle. This produces a combustible mixture which passes through the intake manifold into the cylinders.

The speed of the engine is controlled by the use of the throttle "T" which is a form of damper placed between the mixing chamber and intake manifold. The more the throttle is closed the greater will be the obstacle placed in this passage and the greater will be the opposition to the filling of the cylinder at each stroke. This gives a less powerful impulse to the piston and the engine's speed is correspondingly reduced.

As the throttle is opened the speed of the engine increases and with wide open throttle attains its maximum speed which for this discussion will be assumed to be 1,600 revolutions per minute. The cylinder fills as freely as possible and a large quantity of air passes through the carburetor while the gasoline jet delivers its maximum.

As the load on the engine is increased as will be the case when a hill is encountered, the speed is gradually diminished, say to 400 R. P. M. It is obvious that the air does not pass through the car- buretor with the same velocity as before and the suction is greatly reduced, although the throttle is still wide open. It is evident the throttle does not wholly control the speed of the engine; the load is also a factor that must be considered. In actual test with wide open throttle the engine suction has decreased over nine times between 1600 R. P. M. and 400 R. P. M. The throttle is simply a means to

MOTOR VEHICLES AND THEIR ENGINES

prevent the engine from pulling in a full charge of mixture each suction stroke and thus regulates its power.

As the speed of the engine increases the suction increases. The flow of liquids is governed by definite laws and the flow from a jet increases under suction faster than the corresponding flow of air. With a simple construction of nozzle the mixture becomes richer as the speed increases. As it is essential to have practically the same proportions of air and gasoline at all speeds it is necessary to construct the carburetor to maintain this proportion as the suction increases.

To overcome rich mixtures the carburetor must be adjustable so that less gasoline or more air will be supplied. The gasoline supply is controlled by the size of the spray nozzle opening. For a given suction the quantity of gasoline delivered varies directly as the cross sectional area at the nozzle. In some carburetors the nozzle, which is of fixed size, may be replaced by a smaller or larger nozzle depending upon the regulation desired.

Fig. 42— Types of Needle Valves

In other carburetors the opening at the nozzle is adjustable by means of a needle valve (Fig. 42). As the needle is screwed into its

seat the nozzle area is reduced resulting in leaner mixtures.

The air supply may be controlled by employing an automatic air valve (Fig. 43). This consists of a valve held in its seat by a spring whose tension is adjustable. This valve is opened automatically by Fig. 43 — Auxiliary Air Carburetor atmospheric pressure which

ELEMENTS OF CARBURETION 67

will overcome the tension of the spring allowing air to enter the mixing chamber. As the tension in the spring is increased greater suction will be required to open the valve regulating the point at which the valve opens and the amount it opens.

The auxiliary air entering the mixing chamber does not pass through the Venturi tube hence it dilutes the rich mixture resulting from the increased suction. In this manner the proportions of air and gasoline are kept constant at variable speeds.

PRECAUTIONS WHEN ADJUSTING CARBURETOR.— Before attempting to put a carburetor in proper adjustment certain con- ditions must prevail.

1. The engine must be warm.

2. The adjustment must be made under actual operating conditions.

3. There must be no leaks allowing air which does not pass through the carburetor to enter the combustion space.

4. All choking devices must be wide open.

5. All gasoline passages must be free from obstructions.

6. The ignition system must be properly timed and in working order.

In making carburetor adjustments it is desirable to obtain as lean a mixture as will give proper results. Hence, it is imperative first to diminish the proportions of gasoline to air until so lean a mixture is obtained that missing of the engine and possibly back firing in the carburetor results. The proportion should then be gradually increased until the missing is overcome and the engine runs smoothly.

When making any changes in adjustment it is necessary that only slight changes be made at a time. After every change of adjustment sufficient time must be given for this change to effect the operation of the engine before further changes are made. This will eliminate any possibility of making unnecessary changes. The greatest care must be observed in this respect when overcoming a lean mixture since a mixture richer than necessary may result. This would not be noticed in the running of the engine but would increase the fuel consumption materially.

Carbon monoxide, a deadly poisonous gas, is present in the exhaust of gasoline engines. Increasing the proportion of gasoline to air in the mixture increases the amount of carbon monoxide given off at« the exhaust pipe. Because of the presence of carbon mon- oxide it is very dangerous to run the engine for any length of time while the car is in a small closed garage. If the doors and windows are open the danger is very much lessened, but it is far

68 MOTOR VEHICLES AND THEIR ENGINES

safer if an adjustment of the carburetor is being made to run the car outside.

Serious personal injury may be caused by the presence of carbon monoxide in a garage if the percentage of it in the air is greater than a very small fraction of one per cent. Unconsciousness may result without warning. It is reported that no indication of danger is given by personal discomfort until too late. Deaths resulting from the presence of carbon monoxide in garages have been reported.

During the final test of all motor apparatus by the manufacturer the carburetor is very carefully adjusted and this adjustment should not be changed unless it is absolutely necessary because of greatly changed climatic conditions or grade of fuel used. After the car- buretor is adjusted to operate under these conditions there should be no necessity for further change.

Engine troubles arise from many sources and it is very seldom that the trouble is due to the carburetor adjustment. It must be borne in mind that a properly adjusted carburetor cannot get out of adjustment unless tampered with. It is the tendency of inexperi- enced men to adjust the carburetor no matter what the trouble without first endeavoring to locate the real difficulty. This leads to the adjusting devices becoming worn and inaccurate. Make it an inflexible rule to try to locate engine troubles at all other possible sources before touching the carburetor.

In case the suction through the carburetor is suddenly increased by quickly opening the throttle, the air, being lighter than gasoline, will respond almost instantly and its flow will be accelerated very suddenly. The gasoline particles owing to that characteristic known as "inertia," will not respond so rapidly due to their heavier weight and the flow of gasoline will not accelerate as rapidly as the air. This will result in the air rushing ahead of the gasoline particles and the proportion of air to gasoline will be greater until the inertia has been overcome and the gasoline particles have responded completely to the increased suction. This condition will take place unless some provision is made against it. That is, a sudden opening of the throttle will tend to produce a very lean mixture at the engine due to the lagging of the gasoline. A lean mixture at this time, when acceleration is desired, will be detrimental. It is at this particular time that additional gasoline is most desired in order to compensate for this lagging and maintain the proper mixture at the engine. • The device which accomplishes this result is known as an "accelerating well." The construction or arrangement of this device will be explained as each type of carburetor is taken up.

ELEMENTS OF CARBURETION 69

A rich mixture is required when starting an engine, especially when cold. The additional gasoline may be supplied in several ways ; by priming through the priming cocks, by " flooding" the carburetor, by the use of chokes, or by a dash control which increases the gasoline supply temporarily.

The practice of priming should not be resorted to unless all other methods fail, since the continued addition of liquid gasoline to the cylinders cuts the lubricant, causing loss of compression and permits the gasoline to run past the pistons into the crank case. The result of over-priming makes it almost impossible to start the engine because of the abnormally rich mixture obtained. If an explosion does result the power will not be sufficient to rotate the engine until another power impulse is obtained.

Pet cocks are made with a cup which will hold sufficient gasoline for proper priming. This cup should be filled, the cock opened, and again closed. The common practice of priming without regard to the amount of gasoline used generally results in over-priming. Before starting an engine which has been over-primed the pet cocks should be opened and the engine cranked until the piston and cylinder walls have been lubricated. Turning the engine over for some time also frees the combustion space of the overrich mixture. This must be done as the liquid gasoline adheres to the piston and cylinder walls enriching each incoming charge.

Flooding the carburetor causes the float chamber to be filled with gasoline above the level at which it ordinarily stands. Gasoline will overflow from the spray nozzle by gravity and be picked up by the primary air and carried into the cylinders.

Rich mixtures for starting may also be obtained by the use of chokes. These are placed in the air passages making it difficult to draw air, the suction being satisfied by an increased amount of gasoline vapor. Choking devices are provided on some carburetors to cut down the supply of air until the engine is heated.

All liquids vaporize when heated sufficiently and while gaso- line will vaporize at ordinary temperatures, increased heat improves this vaporization. This tends to reduce the percentage of liquid gasoline in the mixing chamber causing a more intimate combina* tion of the air and gas. This heat may be obtained several ways; by passing air heated by the cylinder or exhaust pipe through the carburetor, by water jacketing the mixing chamber of the car- buretor, by water jacketing the inlet manifold, or by combining the inlet and exhaust manifolds so that the exhaust gases heat the incoming charge.

70

MOTOR VEHICLES AND THEIR ENGINES

There are two common types of float chambers; the concentric in which the float chamber is placed around the Venturi tube and is concentric with it, the eccentric in which the float chamber is placed by the side of the Venturi tube.

Fig. 44 — Effect of Grades on Eccentric Type Carburetor

Fig. 44 shows an eccentric type float chamber and the normal gasoline level is shown by the line in "A." When the carburetor is tilted due to the car ascending or descending a grade the level will be changed as shown in "B " or "C." This causes too much or too little

gasoline to be supplied by the nozzle giving imperfect mixtures. To prevent lean mixtures when ascending grades a carburetor with this type of float chamber should be attached with the float chamber towards the radiator. This difficulty will not be experienced with a concentric float type of car- buretor. The level at the nozzle always remains constant as shown in Fig. 45 by the

Fig. 45— Effect of Grades on Concentric Type Carburetor

different levels A-A, B-B, and C-C. This accounts for the usage of concentric float car- buretors on motor cycles, tractors, or other motor vehicles which are not designed for the ordinary road work.

ELEMENTS OF CARBURETION 71

GOVERNORS. — In order to automatically limit both the vehicle and engine speed at all times, a governor is provided. It consists of a grid or butterfly valve in the inlet manifold controlled by the action of movable weights attached by levers to the driven shaft and valve mechanism. Centrifugal force which results from whirling the weights around the shaft causes them to pull away. This action moves the valve in the intake manifold cutting down the supply of gas.

The position of these weights will depend upon the speed of the engine and at approximately 1200 R. P. M. the gas supply will be cut off, restricting the engine and consequently the vehicle speed. This governing limits the speed of the machine to about 15 miles per hour.

The drive is thru a flexible shaft. It is driven by a set of gears from the cam shaft or by the fly wheel. An adjustment is provided for varying the setting of the governor.

CHAPTER IX

CARBURETORS

The operation and adjustment of the various types of carburetors most commonly used will be outlined giving the particular points in which they vary.

SCHEBLER— MODEL "E"

This carburetor is a concentric float auxiliary air type and is a very simple carburetor. The primary air inlet is through an air bend at the bottom of the carburetor passing the spray nozzle and the auxiliary air inlet, controlled by the usual type of valve, is pro- vided at the top of the mixing chamber. The spray nozzle is regu- lated by the needle valve (Fig. 46).

Air Valve Sprl< Leather Air Value Dk

Auxiliary Air Port Throttle Levef

Throttle Disc Oas Outlet

Lock Spring Loch Nut

Air Value Adjusting Sere iv

Primary Air Inlet Air Bend

Float Valve

'nlon Nut Union Nipple

\

Reversible Union Ell

Needle Valve Packing Nut Gasoline AdjustingNeedle Value

Fig. 46— Sehebler Model E

72

CARBURETORS 73

LOW SPEED ADJUSTMENT.— Have the auxiliary air valve spring tension tight, then adjust by the needle valve turning to the right until the mixture is too lean, and then turn gradually to the left until the missing of the engine is eliminated and the engine runs smoothly.

HIGH SPEED ADJUSTMENT.— Release the tension on the auxiliary air valve spring until so much air is supplied that missing of the engine results and then tighten the spring tension until the engine runs smoothly. With these settings the increasingly rich mixture of the primary should be compensated for by the extra auxiliary air at all speeds.

THE SCHEBLER— MODEL "H"

This carburetor is for motor-cycle use and is of the auxiliary air type having a "lift needle valve." The supply of gasoline is con- trolled by a needle "E" and cam adjustment, which insures the proper amount of gasoline at all speeds. As the throttle is opened the needle rises from its seat.

An air elbow is attached to the primary air passage of the car- buretor so that it can be turned to any convenient angle in order to draw warm air off the cylinders (Fig. 47).

LOW SPEED ADJUSTMENT.— See that the leather air valve "A" seats lightly and then turn knurled button "I" to the right until the needle "E" seats in the spray nozzle cutting off the flow of gasoline. Now turn "I" to the left about three turns and open low speed air adjusting screw "L" about three turns and then open throttle about half way to start the engine. After starting the engine close the throttle and turn needle valve adjusting screw "I" to the right until the mixture becomes so lean that the engine back fires or misses. Then turn adjusting nut "I" to the left slowly, notch by notch, until the engine runs smoothly. If, with this low speed adjustment, the engine runs too fast turn low speed adjusting screw "L" to the right thus ^increasing the size of the throttle opening.

HIGH SPEED ADJUSTMENT.— The carburetor is now ready for high speed adjustment and the throttle should be opened and the spark advanced. The machine should be run at high speed on the road. The adjustment is now made by the pointer "Z" which, as it moves from "1" toward "3," increases the supply of gas as it allows the needle valve "E" to be raised higher out of the nozzle. Moving the indicator "Z" from "3" towards "1" cuts down the supply of gasoline as it raises the cam and does not allow the needle to move as far out of the nozzle. When the indicator reaches the

74

MOTOR VEHICLES AND THEIR ENGINES

correct point the engine will run without missing or back firing. If, when lever " Z" is turned to "3 " the mixture is still too lean, causing the engine to miss and back fire, increase the tension of auxiliary air valve spring by turning adjusting screw "12" to the left.

Fig. 47—Schebler Model H

The air lever on the side of the mixing chamber should be opened when extremely high speed is desired. Be sure to shut this port before the engine is stopped because difficulty will be experienced in starting if this port is left open.

STARTING.— To facilitate easy starting of the engine pull out the knurled button "12" and turn to the right or left so that it cannot fall back in the recess. This tightens the spring on the auxiliary air valve preventing a large quantity of cold air rushing past this valve. The cold air admitted to the carburetor will come only through the primary air passage past the nozzle insuring a rich mixture which will facilitate easy starting.

After the engine starts the knurled button "12" should be turned back to release the spring tension. Just after the engine starts it

CARBURETORS

75

will often be inclined to back fire which is caused by the parts being cold. In this case the knurled button "12" should be dropped into recess marked "2" until the engine warms up.

KINGSTON— MODEL "E"

This is an auxiliary air type of carburetor with concentric float chamber. The construction is shown in Fig. 48.

Fig. 48 — Kingston Model E

The principle involved, while simple, requires some explanation. Gasoline is admitted at connection "24" and continues to flow until valve "22" is seated due to the proper height of gasoline being obtained. From the float chamber the gasoline passes to the spray nozzle the shape of which should be particularly noticed as it forms a cup around the needle valve above its seat, the level being 1/32// below the top of the cup.

When starting this excess of gasoline is drawn up with the primary air and furnishes a very rich mixture. As the speed increases this cup is emptied, the supply being drawn from and regulated by the adjustment of needle valve "7" at its seat.

Both primary and auxiliary air are drawn from a common source passing controller or choke "11." The primary air passes down the primary air passage "3" and up through the Venturi tube.

The auxiliary air in this carburetor is not controlled by a valve but by five balls "2" which are lifted from their seats by suction. These balls are seated at different depths and as the suction increases, they permit a greater amount of air to pass by them. There is no adjustment, their action being automatic and arranged by the manufacturer*

76 MOTOR VEHICLES AND THEIR ENGINES

The only adjustment on this carburetor is the needle valve which should be set to give the proper results at the speed which the ap- paratus will be habitually used. The needle valve when turned to the right, gives leaner mixtures and when turned to the left gives richer mixtures. The action of the auxiliary air should compensate for any change in speed.

PACKARD

This carburetor is of the auxiliary air type with eccentric float chamber. The gasoline flows into the float chamber through a needle valve and then into the nozzle "40" (Fig. 49).

The mixing chamber is surrounded by a water jacket through which passes warm water taken from the water circulation system. This maintains a uniform temperature and insures efficiency in mixing the sprayed gasoline with air. The air has two paths through which it can enter the carburetor, the primary air inlet "33" and the auxiliary air inlet "26." The primary air in passing the nozzle picks up the gasoline. The auxiliary air does not pass the nozzle and there- fore enters the mixing chamber as pure air.

It is important that the mixture of air and gasoline be kept at a constant proportion. Although the primary air inlet valve is large enough to supply air for all conditions, the proportion of air and gas does not remain constant as the suction increases, therefore auxiliary air is necessary. The auxiliary air inlet valve is controlled by springs so that while the valve opens slightly at low speed the increased suction at high speed opens it still more, admitting a greater amount of air, thus compensating for the rich mixture through the primary.

The primary air intake is from around the outside of the exhaust pipe. This provides a supply of warm air which prevents condensa- tion in the carburetor and in cold weather materially assists in the vaporization of the gasoline. There is a regulator "30" so that the proportion of warm and cold air may be regulated.

AUXILIARY AIR VALVE.— The valve is controlled by the tension of two springs one within the other. The tension of the springs is regulated by a wedge underneath them. This wedge is connected to the control board and when it is moved towards the word "gas" the tension of the springs is increased causing richer mixtures. This assists in starting especially in cold weather and the lever should be kept more to the side "gas" than "air" until the engine warms up. This is the only regulation on this carburetor.

To further facilitate starting in cold weather there are chokes in both primary and auxiliary air intakes.

Si/.. i

77

78

MOTOR VEHICLES AND THEIR ENGINES

PEERLESS

This carburetor is of the auxiliary air type with eccentric float chamber (Fig. 59). The gasoline enters the float chamber passing through the screen "1107." The level at which the gasoline is maintained in the float chamber is controlled by the float "1100" which operates the levers "1096" which in turn operate the needle valve "1101." From the float chamber the gasoline passes directly to the nozzle "1110" which supplies gasoline to the mixing chamber.

Fig. 50 — Peerless Carburetor

Air enters the mixing chamber from two sources: the primary air entering at the primary air intake, passing the nozzle located at the center of the Venturi tube "1112," picking up gasoline from the spray nozzle; the auxiliary air enters at the automatic air intake valve " 1079 " which is held in its seat by spring " 1081." The auxili-

CARBURETORS 79

ary air enters the mixing chamber as pure air compensating for the rich mixture from the primary at high speed.

The mixing chamber is water jacketed which assists materially in vaporizing the gasoline and producing a more nearly homogeneous mixture.

The throttle is not of the usual butterfly construction, but con- sists of a valve having two seats. Before leaving the factory the seat "1065" is so adjusted that it will allow the proper amount of mixture to enter the cylinders when idling. The throttle "1064" is controlled by the throttle lever at the top of the steering column or by the accelerator pedal.

To adjust this carburetor the tension on the auxiliary air valve spring is changed. When nut "1085" is turned to the right, it increases the tension on the spring, thus reducing the amount of auxiliary air entering the mixing chamber for a given amount of suction causing the mixtures to become richer. When nut "1085" is turned to the left it weakens the tension on the spring, thus causes leaner mixtures.

To limit the maximum amount that the auxiliary air valve can open, an adjusting nut "1086" is placed on the lower side of the auxiliary air valve. By turning this to the left it will limit the maximum amount that the valve can open, thereby reducing the amount of air which enters at high speed. This adjustment should be made so that it does not effect the operation at any point except extremely high speed.

FIERCE-ARROW

This carburetor (Fig. 51) is of the auxiliary air type with eccentric float chamber. Gasoline enters the float chamber from the tank, the level being controlled in the usual way. Valve "P" is operated by levers "M" which in turn are operated by the float. From the float chamber gasoline passes direct to the nozzle "A-I." The primary air enters through the tube "K-l," passing through the small Venturi tube "L-l," picking up gasoline from the nozzle, and carrying it to mixing chamber "L." The auxiliary air is admitted through the carefully calibrated reed valves "Q-l" and "N-l." There is no method of regulating auxiliary air. The only regulation on this carburetor affecting the mixture is by the needle valve "D-l." When screwed to the right it will give leaner mixtures and when screwed to the left it will give richer mixtures.

This carburetor is equipped with an adjustment for regulating the temperature of the air passing through the primary air inlet.

80

CARBURETORS

81

Cold air regulator "I" is located at the rear of the carburetor; in warm weather the pointer of the regulator should be set to read "open," in cold weather it should be set to read "closed." Any intermediate adjustments can be made according to the temperature. There is also a hot water jacket "T-l" around the mixing chamber. It is connected by pipe "D" from the carburetor to the outlet water pipe and is equipped with a cock. In warm weather this may be closed partially or entirely. By the use of these two adjustments incorrect mixtures encountered because of the lower grades of gasoline can be overcome as vaporization depends upon temperature.

STROMBERG— MODEL "G"

This is an auxiliary air type of carburetor with eccentric float chamber. The gasoline enters the float chamber and passes to the two nozzles "C" and "J."

Fig. 52 — Stromberg Model G

When the engine is idling^ir is drawn through the primary intake passes around the primary nozzle "C" from which a jet of gasoline is spraying. Under load the air valve "E" allows additional air to be sucked in past the auxiliary nozzle "J," producing a mixture which

82 MOTOR VEHICLES AND THEIR ENGINES

unites with the primary mixture formed in the Venturi tube and passes by the throttle valve to the inlet manifold.

There are only two simple adjustments that ever need attention, "A" the low speed adjusting nut and "B" the high speed adjusting nut (Fig. 52). To adjust this carburetor precede as follows: With the engine at rest set the high speed nut "B" so there is at least Vie of an inch clearance between the spring "G" and the nut "X" above it. This is imperative. Set the low speed nut "A" so the air valve "E" is seated lightly.

Start the engine, first closing the choke valve "R" in the air horn by the control provided. Open this as soon as the engine starts and keep open while engine is running. If engine does not start on the third or fourth turn of the crank open this valve and engine should then run.

LOW SPEED. — Do not adjust carburetor until engine is thor- oughly warmed up. When engine is warm and with spark retarded, adjust nut " A" up or down until engine runs smoothly at low speed. To determine proper adjustment open the air valve with finger by depressing "X" slightly. If this causes the engine to speed up noticeably it indicates too rich a mixture and "A" should be turned down notch by notch. If this causes the engine to die suddenly when slightly opening the air valve it indicates too lean a mixture, and "A" should be turned up until this is overcome. Once properly set for idling do not change this adjustment when making the high speed adjustment.

HIGH SPEED. — Advance the spark to the normal position and open the throttle gradually. If engine back fires through the car- buretor it is a positive indication of too lean a mixture and nut "B" should be turned up notch by notch until this is overcome.

If mixture is too rich as indicated by " galloping" of the engine and heavy black smoke from the exhaust, turn "B" down until engine operates properly. A further test for the correct mixture at high speed can be made by depressing the air valve when the engine is running at this speed. If engine speeds up it indicates too rich a mixture, if engine runs slower too lean a mixture.

Turning either adjusting nut up means a richer mixture or more gasoline; down means a leaner mixture or more air.

TO FIND PROPER NOZZLE SIZE.— Carburetors are equipped with the proper size nozzle before leaving the factory and on changes should be made unless absolutely necessary. Before changing examine all manifold and valve head connections for air leaks. It is absolutely impossible to make the carburetor operate properly if there are any air leaks in the engine.

CARBURETORS 83

DOUBLE JET TYPE.— If after following the instructions given for adjustment with the engine running idle at low speed the air valve "E" remains tightly seated it indicates too small a primary nozzle "C" and a larger one should be substituted.

If with the proper adjustment and after stopping the engine the air valve "E" hangs off the seat the primary nozzle is too large and a smaller one should be used.

To change primary nozzle remove pet cock or plug at "P," insert screwdriver, and unscrew nozzle.

If the mixture on low speed is correct but to get the proper high speed adjustment it is necessary to turn nut "B" up so far that the spring "G" is in contact with "X" above it, after the engine is shut down, it indicates that the auxiliary nozzle "J" is too small and a larger one should be used.

If the mixture on high speed is correct but to get the proper adjustment it is necessary to turn nut "B" down so that there is more than y% of an inch clearance between "G" and "X," when the engine is shut down, it indicates too large an auxiliary nozzle "J" and a smaller one should be used.

To change auxiliary nozzle " J" move air horn to one side, remove plug "A-P," insert screwdriver, and unscrew "J." Nozzles are numbered according to drill gauge sizes; for instance, -No. 59 is larger than No. 60.

SEASON ADJUSTMENT.— Open shutter "T" in summer, close in winter. To get best results from this carburetor warm air should be supplied to the hot air horn of the carburetor from around the exhaust manifold.

CADILLAC

This is an auxiliary air type carburetor with concentric float chamber. The gasoline enters the float chamber through the gasoline inlet passage passing the gasoline inlet needle valve. The air is supplied from two sources; the primary air enters at the primary air inlet passing the nozzle at the Venturi tube, the secondary air enters at the auxiliary air valve entering the mixing chamber as pure air.

A leaning device, sometimes called a "gas-saver," is provided which may be adjusted to cause a mixture in which the proportion of gasoline to air is cut down for ordinary driving speeds. The mixture is not affected by the leaning device at the closed or nearly closed position of the throttle, or at the open or nearly open position. The leaning device is adjusted at " G " (Fig. 53) . When the adjusting

84

MOTOR VEHICLES AND THEIR ENGINES

Cadillac Carburetor

AUTOMATIC THROTTLE

THROTTLE 'AUXILIARY AIR VAtvt

•I

FLOA

CATCH BASIN DRAIN PIPE

GASOLINE INLET PASSAGE

GASOLINf INLEl NEEDLE VALVE

-THKOTTtE PUMP

!H- DRAIN PIPE

Fig. 53 — Cross-Section of Cadillac Carburetor

CARBURETORS 85

screw "G" is screwed in as far as it will go the leaning device has no influence on the mixture at any throttle position.

The leaning device consists of a shutter attached to the right hand end of the throttle shaft which covers a slot in the carburetor body when the throttle is opened slightly and then uncovers the slot when the throttle is opened wide or nearly so. A hole is drilled through the carburetor body from the mixing chamber to the slot and another hole is drilled from the float chamber to the slot. When the slot is covered by the shutter, a passage is formed from the mixing chamber to the float chamber. The partial vacuum in the mixing chamber causes a lowering of the air pressure in the float chamber resulting in less gasoline being fed through the spray nozzle. When the shutter uncovers the slot the partial vacuum in the mixing chamber has no effect on the air pressure in the float chamber and the amount of gasoline fed through the spray nozzle is not affected.

This carburetor is equipped with a device to force gasoline through the spraying nozzle when the throttle is opened quickly for acceleration and is called the "throttle pump." It is so arranged that when opening the throttle slowly it will have no effect on the mixture but when sudden acceleration is desired the plunger will be forced down suddenly as the throttle is opened. In this way the gasoline is forced out of the spray nozzle. As the throttle is closed the chamber below the plunger fills up.

The carburetor is equipped with an automatic throttle (Fig. 53) controlled by a spring. Its purpose is to prevent pulsations of air in the intake manifold from causing the auxiliary air valve to flutter when the engine is running slowly with the throttle fully opened. The automatic throttle is adjusted when the carburetor is assembled and requires no further attention.

METHOD OF ADJUSTMENT.— Move the spark lever to the extreme left to retard the spark on the sector and the throttle lever to a position which leaves the throttle in the carburetor slightly open. Adjust the air valve screw "A" to a point which produces the highest engine speed. Turning the screw "A" in a clockwise direction increases the proportion of gasoline to air in the mixture and vice versa.

Close the throttle (move it to the extreme left on the sector) and adjust the throttle stop screw "B" to a point which causes the engine to run at a speed of about 300 revolutions per minute. The spark lever should be at the extreme left on the sector when this adjustment is made.

With the spark and throttle levers at the extreme left on the sector adjust the air valve screw "A" to a point which produces the

86 MOTOR VEHICLES AND THEIR ENGINES

highest engine speed. Open the throttle until the shutter attached to the right hand end of the throttle shaft just covers the slot in the carburetor body. Then adjust the screw " G " to a point which pro- duces the highest engine speed or to a point where the engine misses from too lean a mixture, then overcome the missing by turning the screw "G" in a clockwise direction increasing the proportion of gaso- line to air in the mixture.

During very cold weather when a slightly richer mixture is de- sirable it may be found best to turn the adjusting screw "G" further in a clockwise direction.

SETTING OF CARBURETOR FLOAT.— After the carburetor has been in use for sometime there may be a slight amount of wear at the point of the inlet needle and its seat. If this should occur the height of the gasoline in the carburetor bowl will rise.

To determine if the float is properly set remove the carburetor from the engine and the bowl from the carburetor. Raise the float until the inlet needle valve is just closed. The dimension "A" (Fig. 53) should then be one-half inch. The setting may be corrected by slightly bending the arm to which the float is attached.

MARVEL

This is an auxiliary air type of carburetor with eccentric float chamber. The spray nozzle opening is regulated by a needle valve which constitutes the gasoline adjustment of the carburetor and it is surrounded by the Venturi tube, through which a portion of the incoming air passes at high velocity, picking up gasoline from the end of the spray nozzle.

The mixing chamber also contains the air valve and the high speed nozzle. The auxiliary air valve is held to its seat by an adjust- able spring which forms the air adjustment. At a high rate of speed the suction increases. This causes the auxiliary air valve to lift from its seat admitting additional air mixed with gasoline drawn from the high speed nozzle (Fig. 54).

The air enters the carburetor through a three-way valve connected to the air regulator on the instrument board. By means of this valve the air can be taken from the heater under the exhaust manifold or directly from the atmosphere. In the " choke" position this valve partly closes the air intake causing the engine to draw excessively rich charges for starting.

The opening between the mixing chamber and the intake manifold is controlled by a butterfly valve. This is connected to the throttle lever on the steering wheel and thus regulates the amount of mixture being fed to the engine.

87

88 MOTOR VEHICLES AND THEIR ENGINES

The upper end of the mixing chamber and the Venturi tube are surrounded by jackets through which some of the hot exhaust gas passes to keep the carburetor warm and assist vaporization of the fuel. A damper in the jacket opening is connected to and controlled by the throttle lever so as to increase the amount of heat as the throttle is closed. In warm weather the diamond-shaped shutter on the bottom of the carburetor should be opened to allow the hot exhaust gas to escape before it overheats the nozzle.

ADJUSTMENT OF THE CARBURETOR.— Turn gasoline ad- justment to the right until needle valve is completely closed. Set air adjusting screw so that end of the screw is even with the point of the ratchet spring just above it. Open gasoline adjustment by giving needle valve one full turn. Start engine as usual and allow it to run a few minutes with air regulator turned to "hot" until engine is thoroughly warmed up.

With the spark lever fully retarded turn gasoline adjustment to the right, closing needle valve until engine misses and then turn to left until engine idles smoothly.

Advance the spark lever and turn air adjustment screw to the left, a little at a time, until the engine misses indicating too much air and then turn it to the right until the engine runs smoothly.

To test the adjustment leave spark lever advanced and open throttle quickly. The engine should accelerate instantly. If it skips or pops back open gasoline adjustment slightly by turning needle valve to the left. Do not touch air adjustment again unless it appears absolutely necessary. The best possible adjustment has been secured when gasoline adjustment is turned as far as possible to the right and air adjustment is turned as far as possible to the left. This allows engine to idle smoothly and accelerate quickly when throttle is opened.

CHAPTER X

CARBURETORS (continued)

The carburetors explained in this chapter do not employ auxiliary air valves. The methods used to keep the proportion of air and gas constant at varying speeds is explained as each carburetor is discussed.

STEWART— MODEL 25

This carburetor is of the metering pin type, that is, it meters out the proper amount of gasoline for each speed. The action of the carburetor is as follows: The suction created in the inlet manifold draws air into the mixing chamber through air ducts, drilled holes "H H" (Fig. 55). The same suction draws a fine spray of gasoline through the aspirating tube "L" into the mixing chamber and the air becomes impregnated with the gasoline vapor. In order that the proportions of air and gasoline vapor may be correct for all engine speeds provision is made by means of a valve "A" for the automatic admission of larger quantities of both air and gasoline vapor at high engine speed. The passages "H H" are open at all times, but the valve " A" is held to its seat by its weight until the suction, increasing as the engine speed increases, is sufficient to lift it and admit a greater amount of air by passing around "A" at "L" The valve "A" is joined to the tube "L" hence the latter is raised when the valve is lifted and the increase of proportionally larger quantities of gasoline is made possible. This is accomplished by means of a tapered meter- ing pin "P " normally stationary, projecting upward into the tube "L." The higher the tube rises the smaller is the section of the metering pin even with its opening and the greater is the quantity of gasoline which may be taken into the tube. The taper of the me- tering pin being carefully designed, the carburetor thus automatically produces the correct mixture and quantities for all engine speeds.

There is one adjustment which can be made on this carburetor but which should not be changed unless it is known absolutely that the adjustment is incorrect. The height of the metering pin relative to the opening of the aspirating tube can be changed. To change the fixed " running" position of the pin turn the stop screw to the right or left. Turning this screw to the right lowers the position of the metering pin and turning to the left raises it. As the pin is lowered

A — Air Valve B — Air Valve Seat C — Float Chamber D — Dash Pot E — Combining Tube F — Metal Float G — Gasoline Inlet Valve H— Drilled Holes I — Air Passage K— Air Valve Guide L — Aspirating Tube M — Dash Control Pinion N — Metering Pin Carrier

and Rack

O — Mixing Chamber P— Metering Pin Q — Gasoline Valve Cap S — Gasoline Passage V — Throttle Valve Lever Z — Filler Screen

AA— Air Inlet

CC— Filter Cap

Fig. 55— Stewart Model 25 90

CARBURETORS 91

more gasoline is admitted to the aspirating tube at a given engine speed thus enriching the mixture. A wider range of adjustment of the position of the metering pin may be made by releasing the clamp "M" of the pinion shaft lever and changing its position with relation to the shaft. This requires very careful work and should only be made in extreme cases. The metering pin is also subject to control from the dash and when making any of the foregoing adjustments the dash adjustment must be all the way in.

In starting the engine, especially in cold weather, some difficulty may be experienced. To overcome this difficulty a very rich mixture is required temporarily. To obtain this without disturbing the regu- lar carburetor adjustment a control is provided with an operating plunger on the dash or instrument board. Pulling out the plunger operates the pinion shaft at "M" on the carburetor and lowers the metering pin. This permits more gasoline to be drawn through the aspirating tube than normally. Though the quantity of air drawn into the mixing chamber remains the same a richer mixture results. A mixture of this character ignites much more readily than one having a greater proportion of air, but the resulting explosion does not produce any more power. Therefore, as soon as the engine starts the plunger at the dash should be pushed down.

In very cold weather, the dash adjustment should not be pushed all the way down after the engine starts but should be pushed part way back and left there until the engine warms up. This is necessary because the gasoline does not vaporize as readily in the cold weather.

To prime the carburetor remove Gasoline Valve Cap, "Q" and lift the float needle valve.

HUDSON

This carburetor is of the metering pin type with eccentric float chamber. The gasoline enters the gasoline feed regulator and passes up the "V" groove in the measuring pin. As the measuring pin is lifted it causes a larger opening supplying an increased amount of gasoline. The suction of the engine draws air through the air intake and also from the air chamber above the piston (Fig. 56). As the air is drawn from the air chamber it causes the piston to rise and lift the measuring pin. As the suction increases the greater will be the amount that the piston is raised, proportionately increasing the gasoline supply. As the piston rises a larger area for the air is provided, therefore, the velocity does not necessarily increase with the increased amount of air passing. If the amount of air passing increases and the velocity does not materially increase it will require

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UlX

fi

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a

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LU

CARBURETORS 93

a larger opening at the measuring pin to keep the proper propor- tions. This is automatically controlled by the piston at the same time.

In case the resulting mixture is not correctly proportioned the gasoline feed regulator can be adjusted. If it is lowered it will cause richer mixtures and if it is raised it will cause leaner mixtures. This adjustment is made by the feed regulator lever which is attached to a dash control.

If found necessary to enrich the mixture for starting purposes do not forget to readjust it to the lean position as soon as the engine warms up. Do not have the air control lever in the "choke" or "hot" position after the engine is warm. The increased resistance to the air intake causes a proportionately greater throttle opening than is necessary for the power developed and this results in excessive gasoline consumption.

The only attention necessary on this type of carburetor is to see that the filter under the float chamber is not clogged up, thereby restricting the flow of gasoline, and that the needle valve is seating properly and does not allow the gasoline level to increase and over- flow at the regulating sleeve. It is also advisable to note the action of the carburetor to make sure that the piston valve is acting smoothly and responds to the speed of the engine. It is possible that this piston valve may stick in the cylinder through an excessive accumu- lation of dust which may be caused by driving on a much frequented road. Provided the strangler is used for starting it is very likely this will not be noticed as it is possible to operate this carburetor without any valve action at all. However, if the car is used by an experienced driver who counts upon quick acceleration and good hill climbing abilities the difference will be noticed. This will be especially noticeable if driving without the strangler particularly in cold weather.

To free the valve it is only necessary to remove the cover at the top of the cylinder, withdraw the valve from its place, and clean it with a little gasoline. In putting it back a few drops of kerosene on the top of the piston will help in flushing down any sediment or grit which the gasoline may have left.

STROMBERG— MODEL "M"

This carburetor is of a plain tube construction in which both the air and the gasoline openings are fixed in size. The gasoline is metered automatically without the aid of moving parts by the suction of air velocity past the jets (Fig. 57).

94

MOTOR VEHICLES AND THEIR ENGINES

N

M

AIR

Fig. 57 — Stromberg Model M

To maintain the proper proportion of gasoline and air at variable engine speeds an AIR BLED JET is used (Fig. 58). The principles

of the Air Bleeder are as follows : The gasoline leaves the float chamber, passes the point of the high speed adjusting needle, and rises through the channel "B." Air is taken in through the Air Bleeder "C" and discharged into the gasoline channel through small holes "D." It should be noted that this air is discharged

into the gasoline before the latter reacheg ^ je(. holeg ^ ^ smal,

Venturi tube "E." As the suction of the engine increases drawing a proportionately greater amount from the holes at "E" the propor- tions are kept constant because of the amount of air bled with the gasoline in the channel "B."

The accelerating well (Fig. 59) operates as follows: The action is based upon the principle of the ordinary U-tube. If a U-tube

Fig. SS-Air Bleeder

CARBURETORS

95

contains a liquid and suction is applied to one end of the tube the liquid will rise in that arm and will drop in the other arm. Referring to Fig. 59, the space "F" forms one arm of the U-tube and the space "B" the other arm. These spaces communicate with each other through the holes "G" thus forming a modified form of U-tube.

When the engine is idling or retarding in speed the accelerating well or space "F" fills P with gasoline. When the

/ throttle is opened increas-

m£ ^ne suction in the Venturi tube the following takes place: Atmospheric pressure in the space "F" is exerted through the bleeder forcing the liquid down to join the regular flow from "H" passing up the space "B" and out into the high velocity air stream through the small Venturi tube. While the well acts the flow of gaso- line is more than double the normal rate compen- sating for the lagging of the gasoline due to inertia. Upon close observation it will be noticed that there is a series of small holes down the wall of the well. Referring to the analogy of the U-tube these holes directly connect the two arms of the U-tube. It is obvious that the smaller and fewer these holes, the faster the well will empty due to the U-tube suction, and the larger and more of these holes, the slower the well will empty. It is therefore apparent that the rate of discharge of the well can be regulated, as required by different engines, different grades of gasoline, different altitudes, etc., by inserting wells of different drillings. The action of tjie well is also dependent upon the size of the hole in the bleeder because the area of the hole of the bleeder relative to the areas of the holes in the well determines the rate at which the well will empty.

The operation and arrangement for idling is shown in Fig. 60. Concentric and inside of the passage "B" is located the IDLING TUBE "J." When the engine is idling, that is when the throttle is

B

Fig. 59 — Accelerating Well

H

MOTOR VEHICLES~AND THEIR ENGINES

practically closed, the action which takes place is as follows: The gasoline leaves the float chamber, passes through the passage "H" into the idling tube through the hole "I," thence up through the idling

jet "L." Air is drawn through the hole "K" and mixes with the gasoline to form a finely divided mist which passes on to the jet "L." This jet directs the mist, of gasoline and air into the manifold just above the lip of the throttle valve. In as much as this throttle valve is practically closed, the vacuum created at the entrance of the jet "L" is very high and exceeds 8 pounds per square inch.

It is obvious, therefore, with this condition, that the gasoline will be drawn into the manifold in a highly atomized state. It is well to call attention here to the fact that the LOW SPEED ADJUSTING SCREW "F" operates a needle valve which controls the amount of air pas- sing through the hole "K" and it is the position of this needle

valve which determines the Fig. QO-Idling Jet idjing mixture.

As the throttle is slightly opened from the idling position a suction is created in the throat of the small Venturi tube as well as at the idling jet. When idling, the suction is greater at the idling jet, and when the throttle is open the suction is greater at the small Venturi tube. At some intermediate position of the throttle there is a time when the suction at the idling jet is equal to that at the small Venturi tube, therefore, at this particular time the gasoline will follow both channels to the manifold. This condition (Fig. 61) lasts but a very short while because as the throttle is opened wider the suction at the small Venturi tube rapidly becomes greater than that at the idling jet. The result is that the idling tube and idling jet are thrown entirely out of action and the level of the gasoline in the idling tube drops (Fig. 62) when the throttle is wide open, in which case all of

H

CARBURETORS

97

Fig. 61— Operation at Slow Speed

Fig. 62 — Operation at High Speed

98 MOTOR VEHICLES AND THEIR ENGINES

the gasoline enters the manifold through the holes in the Venturi tube. With the throttle in this position the accelerating well has emptied, and there is a direct passage for air from the Bleeder to the gasoline in the main passage, giving the "AIR BLED JET" feature explained before.

TO ADJUST THE CARBURETOR.— Turn both high and low speed adjusting screws "A" and "B" completely down so that the needle valves just touch their respective seats. Then unscrew (anti-clockwise) the high speed adjustment "A" about three turns off the seat, and turn low speed adjusting screw "B" (anti-clockwise) about one and one-half turns off the seat. The air-horn choke valve should be closed and the engine is set for starting. After the engine has warmed up and the air-horn choke valve is wide open the car- buretor is ready for adjustment.

To adjust the high-speed adjustment "A" proceed as follows: Advance the spark to the position for normal running. Set the gas lever on the steering-wheel quadrant at such a position corresponding to an engine speed of approximately 750 R. P. M. Then turn down (clockwise) on the high-speed screw "A" gradually, notch by notch, until a missing of the engine results. Then turn up or open the same screw (anti-clockwise) until the engine runs at the highest rate of speed for that particular setting of the throttle. This gives an approximate setting of the needle " A."

To adjust the low-speed adjustment "B" proceed as follows: Retard the spark fully and close the throttle as far as possible without causing the engine to come to a stop. If upon idling the engine tends to "roll" or "load" it is an indication that the mixture is too rich and therefore the low-speed adjusting screw "B" should be turned away from the seat (anti-clockwise) thereby permitting the entrance of more air into the idling mixture. This rolling of the engine might also be due to uneven compression in the cylinders, or to the lack of compression in one or more of the cylinders. The low-speed adjust- ment is best made by carefully observing the smoothness with which the engine revolves when idling, and can be properly obtained by turning the screw "B" up or down, notch by notch, until the best idling prevails. It is safe to say that the best idling results will exist when the screw "B." is not much more or less than one and one-half turns off the seat

After satisfactory adjustments have been made with the motor vehicle stationary it is most important and advisable to take the vehicle out on the road for further observation and finer adjustments. If upon rather suddenly opening of the throttle the engine backfires it is an indication that the high-speed mixture is too lean and in this

CARBURETORS

99

case the adjusting screw "A" should be opened one notch at a time until the tendency to backfire ceases. On the other hand if when running along with open throttle the engine " rolls" or "loads" it is an indication that the mixture is too rich and this is overcome by turning the highspeed screw "A" down (clockwise) until this loading is eliminated.

• ZENITH— MODEL "L"

This carburetor is of the compound nozzle type and to fully under- stand its operation a detailed description of the principle upon which it is constructed will be given.

As was explained with a simple construction of carburetor having no regulation (Fig. 41) when the suction increases the air and gasoline increases but the proportion of gasoline increases a greater amount than the air, therefore, the mixture becomes richer.

F

Fig. 63 — Constant Flow Nozzle

If a jet such as shown in Fig. 63 be used in which the opening at "I" is smaller than the opening at the nozzle "H" the follow- ing condition will exist. When the car has been standing the well "J" and nozzle "H" will fill up to the level in the float chamber "F." Although the suction is not high at ordinary speeds say 400 R. P. M. yet it could take up more gasoline from "H" than is permitted to flow through "I." Air is also drawn up through the nozzle from the open well and the mixture is too lean for proper results.

As the speed of the car increases the suction is greater and the quantity of air increases while the gasoline remains the same because

100

MOTOR VEHICLES AND THEIR ENGINES

the tiny stream at "I" is independent of the suction at "H" (the suction at "H" is not transmitted to "I" because the open well "J" allows air to satisfy this suction). The mixture becomes leaner and leaner as the speed or suction increases, the action being directly opposite to that of the simple jet construction.

E K'

Fig. 64 — Compound Jet

In Fig. 64 a construction is shown with the jets combined showing the level of the gasoline when the engine is at rest. The simple jet "G" is supplied through the pipe "E" and compounded with the jet "H" which is supplied by the pipe "K" from open well "J" and compensator "I."

E1 K1

Fig. 65 — Operation at Low Speed

Fig. 65 shows the condition when the engine is under load at 400 R. P. M. with wide open throttle. This suction is not very strong, but it is lifting gasoline from nozzle #W. and also from nozzle "H,"

ft*

CARBURETORS

101

the latter being fed from open well "J." "T&e action of "the com- pensator "I" has held down the supply algasqllntf &$ifap av^l has emptied.

Fig. 66 shows the condition with the engine turning 1600 R. P. M. The suction has greatly increased as shown by the arrows drawing more gaso- line from nozzle "G," nozzle "H" however, still gives the same measured amount because of the action of the compensa- tor "I."

The compound nozzle re- ceives its gasoline from two sources. At any speed both sources of supply are in action. Fig. 66 — Operation at High Speed The main jet "G" (the one

controlled by suction) is selected of the proper size to give just about enough gasoline at high suction. At low suction it will, of course, be deficient. This unavoidable defect of one nozzle, start- ing poor and growing richer until it is almost right at high suction, is compensated for by the peculiarity of the other jet "H" which also starts poor and keeps growing poorer. The compensator " I " sup- ports the main nozzle "G" at low suction when it is most needed. One supplements the other so that at every engine speed there is a constant ratio of air and gasoline to stimulate efficient combustion.

IDLING DEVICE.— At low speed when the butterfly throttle valve "T" is nearly closed the main jet and cap jet gives but little or no gasoline, but as there is con- siderable suction on the edge of the butterfly, the gasoline is drawn through the idling device. This device (Fig. 67) consists of the idling tube "J" within the secondary well "P" inserted in the first well Fig. 67— Idling Device

102

MOTOR VEHICLES AND THEIR ENGINES

at the bottom of whic^the compensator "I" is located and which is openitkxjat^spbpi-e pressure through holes "A."

Gasoline from the compensator "I" flows through the calibrated hole in the bottom of the secondary well "P" which in turn is ad- justably open to the air through the idling screw "O." The idling tube "J" leads to a hole located at the edge of the butterfly throttle valve where the suction is most strongly felt. This suction lifts the gasoline through the idling tube and, in combination with the air passing the butterfly valve, forms the idling mixture.

There are four adjustments which are possible with this type of carburetor.

1. Choke tube "X."

2. Main jet "G."

3. Compensator " I."

4. Regulator screw "0."

CHOKE TUBE TOO LARGE.— The "pick up" will be defective and cannot be bettered by the use of a larger Compensator. Slow

Fig. 68— Zenith Model L

CARBURETORS 103

speed running will not be very smooth. The engine will have a tendency to "load-up" under a hard pull and at high speed the exhaust will be of an irregular nature. This "loading-up" will be much worse if the manifold is too cold.

CHOKE TUBE TOO SMALL.— The effect of a small Choke Tube is to prevent the engine from taking a full charge with the throttle opened wide. The "pickup" will be very good but it will not be possible to get all the speed of which the car is capable. Remember that when the Choke (Venturi tube) is increased more air is admitted and the mixture is correspondingly thinned. The influence of the Main Jet is mostly felt at high "speed.

MAIN JET TOO LARGE.— At high speed on a level road it will give the usual indications of a rich mixture; irregular running, characteristic smell from the exhaust, firing in the muffler, sooting up at the spark plugs, and low mileage.

MAIN JET TOO SMALL.— The mixture will be too lean at high speed and the car will not attain its maximum speed. There may be back-firing at high speed, but this is not probable especially if the Choke and main jet are according to the factory setting. This back- firing is more often due to large air leaks in the intake or valves or to defects in the gasoline line.

The compensator size is best tried out on a long gradual hill of such a slope that the engine will labor rather hard to make it on high gear. A long, even, hard pull of this sort taxes the efficiency of the Compensator to the utmost and will indicate readily the correctness of its size.

COMPENSATOR TOO LARGE.— This will cause too rich a mixture on a hard pull. It will give the same indication as for rich mixture at high speed on the level.

COMPENSATOR TOO SMALL.— This will cause too lean a mixture making the engine liable to miss and give jerky action of the car on a hard pull.

IDLING DEVICE IS TOO SMALL.— It will be impossible to obtain a satisfactory mixture except by turning the Idling (adjusting) Screw all the way in. In this event put in a larger Idling Device.

IDLING DEVICE IS TOO LARGE.— It will be impossible to obtain a satisfactory mixture unless the Idling Screw is turned out as far as possible. In this case put in a smaller Idling Device.

It has been found from practice that it is rarely necessary to make adjustments on this carburetor as the conditions are carefully cal- culated when installing the carburetor by the engine manufacturer, however, in a few cases where the climatic conditions or the grade of

104 MOTOR VEHICLES AND THEIR ENGINES

gasoline vary greatly from the ordinary standards, the Compensator "I" and the Jet "G" may have to be changed.

RAYFIELD

The Rayfield carburetors are made in two types, models G and L. The difference is that model G is water-jacketed (Fig. 69). These carburetors are of the mixed type, having both auxiliary air valves and metering pins. The gasoline supply enters through the gasoline intake passing the needle valve which is operated by the float. Gasoline is supplied from the float chamber to the two nozzles, marked in Fig. 69 as "spray nozzle" and " metering pin nozzle."

Air enters the mixing chamber from three sources: Through a constant air opening which is a hole in the side of the carburetor so that the air in entering the mixing chamber passes the spray nozzle. Air also enters through the upper automatic air valve, this air passing the metering pin nozzle. The lower air valve admits air directly to the mixing chamber and is operated by levers which are controlled by the automatic air valve.

The operation of this carburetor is as follows: With a closed throttle and the engine idling, air enters through the constant air opening picking up gasoline at the spray nozzle. As the speed is increased and the throttle opened wide, the increased suction will cause the automatic air valve to open. This valve in opening causes the lower air valve to open and at the same time forces down the metering pin which increases the opening at the metering pin nozzle, causing a greater amount of gasoline to be supplied. When suddenly accelerating the operation is as follows: The automatic air valve opening suddenly causes the dash-pot piston to force gasoline out of the metering pin nozzle, thus enriching the mixture which will compensate for the lag of the gasoline due to inertia.

ADJUSTING LOW SPEED.— With throttle closed, dash control down, close nozzle needle by turning low speed adjustment to the left until block "U" slightly leaves contact with cam "M." Then turn to the right about 3 complete turns. Start engine and allow it to run until warmed up. Then with retarded spark close throttle until engine runs slowly. With the engine thoroughly warm make final low speed adjustment by turning low speed screw to left until engine misses and then turn to right a notch at a time until engine idles smoothly. If the engine does not throttle low enough turn stop arm screw "A" to the left until the engine runs at the lowest number of revolutions desired.

HIGH SPEED ADJUSTMENT

TURN TO RIGHT FOR.

MORE GAS

LOW SPEED ADJUSTMENT

(LOWER AIR VALVE] MODEL G

Fig. 69 — Rayfield Carburetor

105

106

MOTOR VEHICLES AND THEIR ENGINES

ADJUSTING HIGH SPEED.— Advance spark about one-quarter. Open throttle rather quickly. Should engine miss, it indicates a lean mixture. Correct this by turning high speed adjustment screw to the right one notch at a time until the throttle can be opened quickly without the engine missing. If "loading" or "choking" is experienced when running under heavy load with throttle wide open, it indicates too rich a mixture. This can be overcome by turning high speed adjustment to the left.

TO START ENGINE WHEN COLD.— First, close throttle and pull dash control all way up. Second, when engine starts open throttle slightly and push dash control J4 way down. Third, as engine warms up push control down gradually as required. When thoroughly warm push dash control all way down. When engine is warm it is necessary to pull dash control only part way up for starting.

SCHEBLER— MODEL A, SPECIAL

This carburetor is of the plain tube type with eccentric float chamber. All the air enters at "I" and passes through the Venturi tube past the nozzle to the inlet manifold (Fig. 70). The gasoline supply enters at "12" passing through the screw "11" and enters the float chamber. The proper level is maintained in the usual manner by a float "15" operating a needle valve "13." From the float chamber the gasoline has two paths; one is past Idle adjusting needle valve "9" to passage "7," the other is past main fuel adjusting needle valve "14."

When starting, the choke should be closed (Fig. 71), especially in cold weather and the throttle "19" nearly closed. This shuts off the air supply and the suction causes gasoline to be drawn through

passage "7" and out the opening just above the throttle. Some gasoline will also be drawn from the three holes "21" and the lip "6." This gives a rich mixture which makes starting easy. When running idle the throttle is closed. This only permits a small amount of air to pass through the Venturi tube, its velocity not being sufficient to draw gaso- Fig. 71 — Operation Choked line from the main jet. The

107

108 MOTOR VEHICLES AND THEIR ENGINES

Fig. 72 — Operation Running Idle

Fig. 73 — Operation Under Partial Load

greatly restricted area at the throttle creates a suction at the open- ing of passage "7." Some of the air entering will pass under the edge of the Venturi tube (Fig. 72) into passage "18," thence through passage "7" mixing with the gasoline. This mixture is delivered through the opening just above the throttle.

As the throttle is opened the amount of mixture drawn through the Venturi tube is increased. The velocity of the air now being sufficient to cause a suction which will draw fuel through the three holes "21" (Fig. 73). The incoming air strikes the projecting lip

on the nozzle housing and due to its velocity enters the hole "6." Due to the U-tube con- struction contained in the nozzle housing, the level of gasoline in the arm connected to the opening "6" will be lowered uncovering holes be- tween this arm and arm "20." As these holes are uncovered the air passes through them mixing with gasoline in passage "20." Instead of pure gaso-

Fig. 74— Operation Under Full Load line beinS delivered at holes

"21," a spray of air and gasoline

is delivered which mixes with the air being drawn through the Venturi tube. Some mixture may be delivered by the idling jet, decreasing as the throttle is opened.

When the throttle is wide open (Fig. 74) the increased amount of air passing through the Venturi tube causes a much greater suction

CARBURETORS 109

at the holes ".21," likewise the pressure at the hole "6" is increased causing the level to be lowered still further in the U-tube. This permits more air to be drawn through the communicating holes mixing with the gasoline in the passage "20." Thus the proportion of air and gasoline delivered to the mixing chamber is kept constant as an increasing amount is drawn through the holes "21." If only pure gasoline was drawn the mixture would become richer but as both air and gasoline are drawn from holes "21," this air bleeding keeps the mixture constant at all speeds.

ADJUSTMENT.— There are but two adjustments on this car- buretor both of which control the amount of gasoline supplied. The idle adjusting needle valve "9" regulates the supply of gasoline for idling and the main needle valve "14" regulates the amount of gasoline supplied to the main fuel nozzle "4."

Screw out both Adjusting Needles several turns. Start the en- gine with the throttle slightly open. Slowly turn the Idle Adjusting Head "17" to the right or towards the "less gas" position as indi- cated by the dial until the engine runs smoothly. Adjust the engine speed for running idle by means of the throttle lever Stop Screw on the throttle lever. Open the throttle wide allowing the governor to regulate the engine speed and with a retarded spark turn the Main Gas Adjusting Head "16" toward the "less gas" direction until the engine begins to miss or backfire. Turn the adjusting head in the "more gas" direction just sufficient to stop the engine missing or backfiring. These adjustments should produce a good mixture.

For starting or warming up with the present day fuel it is almost always necessary to use the air choke until proper operating tem- perature is obtained. The engine will start readily with the choke closed one-half to three-quarters of the way. When the weather is very cold it may be necessary to close the choke entirely, but this should be done only for an instant, as it cuts off all the air and delivers practically raw gasoline.

WHITE

The White is an eccentric float, multi-jet type of carburetor (Fig. 75). Air enters at opening "47," which is .provided with a choke "42." The gasoline flows from the float chamber to the low speed nozzle "29" and high speed nozzle "28." A small drilled hole "62" in the side of low speed nozzle "29" near its base supplies gasoline to a passage leading to a vertical well "64" in the side of the car- buretor body.

The nozzles are incased in nozzle sheaths "34" and "33." Low speed nozzle sheath "34" is open at the top but closed at the bottom

110

MOTOR VEHICLES AND THEIR ENGINES

to air entering at "47." High speed nozzle sheath "33" is open at the top and drilled with holes "63" at the bottom permitting some of the air to be drawn up inside the sheath discharging at its top. Ths starting nozzle "65" dips into the vertical well "64" and sup-

34 33

Fig. 75— The White Carburetor

plies gasoline through a small drilled hole just above the throttle valve. Screened hole "106" opening into the top of the well, main- tains atmospheric pressure at all times. The throttle valve "2" is of the barrel type, consisting of a metal cylinder with twin openings cut through it of the proper shape to admit mixture. As the throttle is revolved on its axis the opening from the low speed nozzle is gradually uncovered. At a certain point the opening to the high speed nozzle is uncovered and at wide open throttle position, both passages are completely uncovered. A screw "36" is provided regulating the amount of air supplied with the throttle closed and the engine idling.

A — IDLE

S L P

B — Low SPEED

C — MEDIUM SPEED

H L P

D — HIGH SPEED

Fig. 76 — Operation of White Carburetor ill

112 MOTOR VEHICLES AND THEIR ENGINES

Referring to the diagrams in Fig. 76 the operation of the car- buretor is as follows:

For idling or starting the throttle is completely closed (Fig. 76 A). Suction in the intake manifold causes a reduction in pressure above the throttle "T." Atmospheric pressure exerted at the top of well " W" causes gasoline to rise in the starting nozzle "N." At the same time, air is drawn past the regulating screw (not shown) and through the drilled hole "D" producing a mixture for starting and idling. The choke must be closed when starting, reducing to a minimum the amount of air drawn through "D."

' For low speed the throttle is turned so that the low speed passage is partially uncovered (Fig. 76B). A considerable volume of air is drawn past the low speed nozzle sheath "S" causing low speed nozzle "L" to deliver gasoline which passes out the opening at the top of the sheath and mixes with the incoming air. The well "W" is almost immediately emptied, a small quantity of air probably being drawn in through the passage "P." The high speed nozzle "H" is still completely covered.

As the throttle is turned to the medium speed position, the low speed passage is further uncovered and the high speed passage is uncovered slightly (Fig. 76C). The low speed nozzle "L" functions as before, the increased suction causing it to deliver more mixture. Additional air and gasoline is supplied through the partially un- covered high speed passage, air passing in at the bottom of the sheath "R."

As the throttle is turned to the high speed position, both low and high speed passages are completely uncovered, bringing both nozzles fully into action (Fig. 76D). The maximum volume of air is drawn through both the low and high speed openings. Low speed nozzle "L" draws as much air as possible through passage "P" and high speed nozzle "H" delivers its maximum. It is probable that the air passing through the sheath "R" increases the suction on high speed nozzle "H." If the throttle is suddenly opened wide a large volume of air will rush in past "R" before a flow of gasoline from "H" is established. This will cause the engine to "die."

ADJUSTMENT.— The only adjustment on this carburetor is made by the Idle Adjusting Screw "36" with the engine running and the car standing still. If there is too much air, this screw should be turned to the right or in. If there is not enough air, it should be turned to the left or out. Further regulation of the quantity of air and gasoline for every position of the throttle valve is automatic. Too rich a mixture may be caused by dirt in the air inlet screens. These should be kept clean.

CARBURETORS 113

In extreme cases, the nozzles "34" and "33" may be replaced by others of different drillings. Both the hole at the top of low speed nozzle "34" and hole "62" in its side near the base vary in size. The high speed nozzle "33" is seldom changed.

The air coming in at "47" is supplied through a tube running to a s