70 / 
 
 AVIATION 
 
 ENGINES 
 
 JOHN C, CHADWFCK 
 LIEUT. (J.G.) U,S.N, R,P 
 
 UC-NRLF 
 
 E77 137 
 
 IMC, 
 
 NEW YOHK, 
 
AVIATION ENGINES 
 
 JOHN C. CHADWICK 
 
 LIEUTENANT (J.G.) U. S. N. R. F. 
 
 Published by Authority of the Secretary of the Navy 
 
 PUBLISHED BY 
 EDWIN N. APPLETON, INC. 
 
 ONE BROADWAY 
 NEW YORK CITY 
 
/ 
 
 COPYRIGHT, 1919 
 
 BY 
 EDWIN N. APPLETON, INC. 
 
'"THE author wishes to express his thanks and appreciation 
 to the following concerns who furnished photographs and 
 other material making possible the writing of this book: 
 
 The Zenith Carburetor Co., Detroit, Mich. 
 
 The Packard Motor Car Co., Detroit, Mich. 
 
 The Curtiss Aeroplane and Motor Corp., Garden City, L. I. 
 
 The Manufacturers' Aircraft Association, New York City. 
 
 416880 
 
CONTENTS 
 
 PAGE 
 
 Introductory 9 
 
 Nomenclature 10 
 
 Definitions 14 
 
 Principle of Operation of a Four-Stroke Cycle Engine 15 
 
 Valve Location 17 
 
 Propeller Drive 18 
 
 Multi-Cylinder Arrangement 20 
 
 Cooling 22 
 
 Radiators 22 
 
 Water Circulation 22 
 
 Water Pumps 23 
 
 Operation of Cooling System 23 
 
 Lubrication 24 
 
 Carburetion 26 
 
 Effects of Improper Carburetion 33 
 
 Electricity and Magnetism 35 
 
 Induction 35 
 
 Ignition 36 
 
 Magnetos 41 
 
 Dixie Magneto 42 
 
 Timing 44 
 
 Emergency Repairs 49 
 
 Engine Characteristics 
 
 Liberty 51 
 
 Liberty-Delco Ignition System 62 
 
 Order of Teardown U. S. N. Liberty Motor School... 72 
 
 Teardown U. S. N. Liberty Motor School 73 
 
 Hispano Suiza 79 
 
 Curtiss Model OXX6 83 
 
 Materials of Construction 86 
 
 Trouble Charts . . 88 
 
PREFACE 
 
 IN writing this book the author has endeavored to set 
 forth the underlying principles of the Internal Combustion 
 Engine as used in Aviation. The actual engines discussed 
 are those that were used most widely by the United States 
 Naval Aviation Corps during the recent war. They may be 
 taken as very representative and highly efficient engines cover- 
 ing the field of American aviation in general at the present 
 time. The Rotary Engine is not discussed, since its use was 
 discontinued by our Navy, although it was widely used in light 
 foreign planes, particularly those of French design. 
 
 The author has endeavored to set forth in non-technical 
 language and without the use of mathematics, the main features 
 of the principles employed in any internal combustion gasoline 
 engine, and show their adaptation, in the three engines speci- 
 fically discussed : the Liberty, Curtiss model OXX, and Hispano 
 Suiza. 
 
 The purpose of this book is to give anyone desiring to 
 operate an airplane, a fundamental understanding of engines as 
 used. It is founded on the course of instructions as given at 
 the U. S. Naval Aviation Detachment, Massachusetts Institute 
 of Technology, in Training Pilots for service. It is not intended 
 for purposes of design, criticism or recommendation, but simply 
 for instruction of the average individual, assuming he knows 
 nothing of a gas engine. 
 
 For books pertaining to the mathematics of design, the 
 author recommends: 
 
 Judges "High Speed Internal Combustion Engines." 
 "The Gasoline Motor," by P. M. Heldt. 
 
AVIATION ENICINES 
 
 INTRODUCTORY 
 
 Engines used in Aviation are all of the internal combustion 
 type. By internal combustion is meant that the combustion or 
 burning of the fuel takes place in the engine itself. The fuel 
 used is gasoline (hydro carbon), and when mixed with air 
 becomes highly explosive. 
 
 The mechanical parts of the engine consist of a cylinder, 
 piston, connecting rod and crank shaft. The explosive mixture 
 is drawn into the cylinder, one end of which is closed by the 
 cylinder head, and the other end plugged by the piston. The 
 explosive mixture is ignited by an electric spark and the ex- 
 pansion of the burning charge causes the piston to move down 
 in the cylinder, just as the charge of powder in a gun causes 
 the projectile to move down the barrel of the gun. As the 
 motion desired to turn a propeller (which is used for the pro- 
 pulsion of the aeroplane) is rotary, the travel of the piston is 
 converted into rotary motion by connecting the piston to a 
 crank shaft, with a connecting rod. The motion of the piston 
 then becomes reciprocating, up and down in the cylinder. 
 
 An internal combustion engine is, therefore, an engine that 
 obtains its power from the rapid combustion and consequent 
 expansion of some inflammable gas; and must have, in addition 
 to the parts named above, ports and valves, whose opening and 
 closing are so controlled as to admit the explosive gas into, the 
 cylinder and to expel the burnt gas. The degree of heat gen- 
 erated by the explosion of a charge is extremely high in fact 
 higher from the melting point of some metals, and it can 
 
 9 
 
therefore- l be seen: t *K& continued series of explosions would 
 SOQYI c^u&e4;he^eKlne,to, become heated to such an extent that 
 it ^couki\ L nt)t ^pe'r^o It, is .therefore necessary to keep the 
 temperature of the engine within safe working limits, and for 
 this purpose a cooling system becomes necessary. The engine 
 must be very carefully oiled, and for this purpose a lubricating 
 system is necessary. As the fuel used is hydro carbon, a device 
 must be used to convert the hydro carbon into a combustible 
 gas. The device is called a carburetor and is referred to as 
 the carburetion system. After the gas had been introduced 
 into a cylinder, some means for igniting it must be provided in 
 order that it may explode. This apparatus is called the igni- 
 tion system. It can be seen from the above that there are four 
 systems that are absolutely necessary in the construction of an 
 internal combustion engine. 
 
 NOMENCLATURE 
 
 There are of course a great many parts to an engine 
 besides those mentioned or alluded to in the introductory. The 
 names of the various parts are in the most part self-explana- 
 tory. 
 
 It has been shown that it is necessary to have a cylinder 
 in which the explosion and expansion of gases may take place, 
 and in which the piston may travel. 
 
 It is necessary to have an intake valve and port so that 
 incoming gases may be admitted properly to the cylinder. This 
 makes necessary an intake manifold, or pipe, for conducting 
 the gases from the carburetor to the intake port. Likewise it 
 is necessary to have an exhaust valve and port, and in many 
 cases an exhaust manifold to carry away the exhaust gases. 
 
 The piston must then be fastened to the connecting rod. 
 This is done by means of the piston pin and, in order that steel 
 may not meet steel, a fine bronze or brass sleeve is placed in- 
 side the hole of the upper end of the connecting rod. This is 
 
 10 
 
known as a bushing. The lower, or big end of the connecting 
 rod, is then fastened to the crank shaft. Again so that steel 
 surfaces will not be in contact a bearing of softer metal is 
 used. In this case, for ease of assembly and because of the 
 larger surface, a bronze or brass shell, which is split, is lined 
 with babbit or white metal and provides the rubbing surface. 
 This is known as the connecting rod bearing. 
 
 The crank shaft is the revolving part of the engine and 
 consequently it must be supported. This is done by means of 
 bearings placed in webbing of the crank base, and these bear- 
 ings are known as main bearings. The crank shaft receives its 
 power from the piston and connecting rod. Consequently it 
 must have offsets or throws so that the heretofore straight line 
 motion may become rotary. The part of the crank shaft which 
 rests in the main bearings is known as the journal. The part 
 to which the connecting rod is attached is called the crank 
 pin and the parts connecting the two are called the cheeks. 
 
 Now it is necessary to have the valves actuated at the 
 proper moments. This is done primarily by means of the cam 
 shaft. This is a shaft upon which cams or eccentrics are 
 placed. The shaft revolves, being geared to the crank shaft. 
 Then when the high part or toe of the cam hits the lever or 
 valve actuating mechanism, the valve is forced off its seat and 
 remains open as long as the high point of the cam stays in 
 position. The valve is opened always against the action of a 
 spring, which closes it as soon as the cam is in a position to 
 permit. 
 
 Following is a summary of the important parts of an 
 engine. A glance at the accompanying cuts \vill show their 
 assembly and co-ordination. 
 
 Cylinder: That part of the engine in which combustion and 
 expansion occurs; and in which the piston reciprocates. 
 
 Valves and Valve Ports: Located in cylinder head to allow 
 control of incoming: and exhaust gases. 
 
 11 
 
End View 
 
 Cross Sections. 
 
 A- CYLINDER 
 
 S- PISTON 
 
 C -CONNECTING ROD 
 
 D-CRAMK PIN 
 
 F-MAIIN BEARING 
 G- THRUST i. 
 H-CRANK CASE 
 I - SUMP 
 J- CAM SHAFT 
 
 K- ROCKS R 
 
 L- VALVE SPRING 
 
 N - C 
 
 O- WATER JACKET 
 
 P- PISTON PIN 
 
 <J- VALVE , 
 
 M- CRANK SHAFT 
 
 S- WATER MANIFOLD CONNECTFOf 
 
 12 
 
A Cylinder. D Rocker Arms. F Valve Springs. 
 
 B Valves. E Valve P^rts. H Cam. 
 
 I_\Vater Jackets. J Valve Clearance. 
 
 13 
 
Piston: That part upon which expansion acts, causing 
 downward action. 
 
 Connecting Rod: Connects piston to crank shaft, thereby 
 converting reciprocating motion into rotary motion. 
 
 Crank Shaft: That member which receives rotary motion 
 from the connecting rods and transmits it to the propeller 
 either direct or through gearing. 
 
 Crank Case: Housing which furnishes a means of support 
 for the crank shaft and cylinder. 
 
 Sump: Lower part or apron for the crank case, deriving 
 its name from the fact that it is very often the oil reservoir. 
 
 Cam Shaft: Prime mover for the valve operation. 
 
 Timing Gears: Gears by means of which the proper speed 
 of rotation is transmitted from the crank shaft to the cam 
 shaft. 
 
 Rocker Arm: Lever mechanism for opening the valve. 
 
 Valve Spring: Spring for closing the valve. 
 
 Intake Manifold: Pipe or passage through which gases 
 are drawn into cylinder. 
 
 Water Manifolds: Pipes through which water is distrib- 
 uted to and from cylinders. 
 
 Thrust Bearing: A ball-bearing that receives the push or 
 pull of the propeller. 
 
 DEFINITIONS 
 
 Cycle of Operations: Series of events which occur in an 
 engine from one intake stroke to the next. 
 
 Top Dead Center: Uppermost point of piston travel. 
 
 Bottom Dead Center: Lowermost point of piston travel. 
 
 Bore: Inside diameter of cylinder. 
 
 Stroke: Distance travelled by piston from top to bottom 
 dead centers. 
 
 Piston Displacement: Generally referred to as meaning 
 the total piston displacement of an engine, which is the volume 
 
 14 
 
of the space displaced by the piston in one stroke times the 
 number of cylinders. 
 
 Back Fire: Pop back or explosion in intake manifold or 
 carburetor. Caused by improperly seated intake valve or mix- 
 ture too lean. Causes a great many engines to catch fire and 
 is a dangerous condition. 
 
 Back Kick: Rotation of .the engine in wrong direction, 
 caused by pre-ignition, or spark advanced too far. Dangerous 
 especially when cranking by hand. 
 
 After Firing: Is the engine running after the switch has 
 been cut, and is due to carbon particles in the combustion 
 chamber or overheating. All aviation engines will continue 
 to run after the switch has been cut unless they are allowed to 
 run slowly for a few minutes and cool. After firing is very 
 injurious to the engine and very often results in the breaking 
 of timing gears, and other parts. 
 
 Idling: When an engine is running at a low speed (200 
 r.p.m. to 800 r.p.m., according to the make of engine) it is said 
 to be idling. 
 
 Contact: Ignition switches in the starting position, throttle 
 nearly closed ready for starting. 
 
 Off: Ignition switch in off position. 
 
 Throttle open: Throttle controls in wide open position, for 
 purpose of drawing in a charge of gas for starting. 
 
 Spark retarded: Spark controls at point of extreme retard. 
 
 PRINCIPLE OF OPERATION OF A FOUR- 
 STROKE CYCLE ENGINE 
 
 It has already been mentioned that power is obtained from 
 the explosion and consequent expansion of a gas, which is the 
 mixture of gasoline and air. Obviously it is necessary to clean 
 the burned gas out of the cylinder when its power has been 
 utilized. Also it is necessary to admit and draw a new charge 
 into the cylinder. 
 
 15 
 
There also is another important matter to be considered, 
 namely, that all possible power must be obtained from the ex^ 
 panding gas. It has been found that by compressing a charge 
 before igniting it the power derived will be vastly increased.; 
 Consequently there is still another item to be considered and 
 which must be performed in the cylinder, vk. : compression. 
 
 From the foregoing it can be seen that it is necessary to go< 
 through four distinct operations to obtain one power impulse.! 
 Gas must be taken in; this gas must be compressed; power o| 
 work can then be derived from the ignition and expansion o; 
 the gas; and then the burned gases must be expelled. 
 
 All of these operations in a four-stroke cycle engine an 
 
 performed by four strokes of the piston. Bearing in mind tin 
 
 fact that the piston is attached to the crank shaft by the con^ 
 
 necting rod it will be seen that the crank shaft consequent!' ' 
 
 makes two revolutions in this time. The four strokes nece:' 
 
 sary to complete one cycle then are : 
 
 1 Intake, 
 
 2 Compression, 
 
 3 Power, 
 
 A Exhaust. 
 
 Consequently there is but one impulse per cylinder to every 
 two revolutions of the crank shaft. Practically all aviation 
 engines used at present operate upon this principle. 
 
 It may be noted here also that there is a point of upper- 
 most travel and a point of lowermost travel for the piston at 
 the beginning and end of each stroke. The uppermost point 
 is known as Top Dead Center or just Top Center. Likewise j 
 the lowermost is Bottom Dead Center or Bottom Center. 
 
 The cycle of operations begins with the piston in the 
 uppermost position in the cylinder. At this point a valve put- 
 ting the cylinder in communication with the carburetor opens. 
 The piston then travels down in the cylinder drawing in a ] 
 charge of gas from the carburetor. When the piston reaches 
 the end of its downward stroke, the valve closes; the cylinder 
 
is then closed and the piston on the following up stroke com- 
 presses the charge and, at approximately top center, a spark 
 occurs in the cylinder, igniting the charge; the piston is then 
 subjected to the pressure of the burning, expanding gas, and is 
 forced down in the cylinder; this is the power stroke. At the 
 end of the power stroke the piston is again at bottom center. 
 At approximately the end of the power stroke, another valve 
 opens a port communicating with the atmosphere, and the pis- 
 ton on the next up stroke forces the burnt gas out of the cylinder, 
 and this valve closes at approximately top center. The engine 
 has then completed one cycle and is ready for the next. 
 
 Beginning with the piston at top center, the cycle of 
 events, piston and valve movements can be followed thus: 
 
 Event Piston Stroke Position of Valves 
 
 1. Intake 1. Down Intake valve open 
 
 2. Compression 2. Up. Both valves closed 
 
 3. Power 3. Down Both valves closed 
 
 4. Exhaust 4. Up Exhaust valve open 
 
 VALVE LOCATION 
 
 Valve location has a great deal to do with the power output 
 of an engine. In early practice, valves were located in pockets 
 at the side of the cylinder head proper. Cylinders of this char- 
 acter come under two main headings. Where the exhaust valve 
 is on one side and the intake on the opposite side the cylinder 
 is termed "T" head. Where the exhaust and intake valves are 
 both on the same side, the cylinder is termed "L" head. Both 
 the above types have disadvantages because of the pocket for- 
 mation, which hinders scavenging and power development. In 
 the above cases the valves are operated by simple adjustable 
 lifters transmitting the cam action to the valve stems. 
 
 In later practice the "L" head and "T" head have practi- 
 cally given way to the "I" head, in which the two halves are 
 located directly in the head of the cylinder proner and operate 
 
 17 
 
downward. In this type of cylinder the valves are operated by 
 means of an overhead cam shaft with rocker arms; or if the 
 cam shaft be located in the crank case, by means of a system 
 of pushrods and rocker arms. 
 
 A rocker arm is" simply a lever, pivoted near the middle, 
 one end riding on the cam surface and transmitting the cam 
 action to the valve stem by means of the other end. The part 
 which comes in contact with the valve stem is called the tap- 
 pet. It is usually in the form of a small bolt so that it may be 
 adjustable. This is necessary to give valve clearance or a 
 clearance between the valve stem and the tappet. Valves are 
 subjected to high temperatures and therefore must expand. It 
 is necessary to allow for this expansion. If no valve clearance 
 were allowed expansion would take place and the valve would 
 be held open, or off its seat, too long or all altogether. This 
 would result in loss of compression and consequent loss of 
 power. It may then be seen that valve clearance is very 
 important and must be kept adjusted. Valve clearances differ 
 with various engines, but are always specified by the manu- 
 facturer. Usually the exhaust valve clearance will be the 
 greater since this valve is subjected to greater heat than is the 
 intake. It is just as important for proper operation not to 
 have too much valve clearance since this would allow the valve 
 to open late and close early.. 
 
 To insure against loss of compression the valve must make 
 a gas-tight fit on its seat. To accomplish this, valves are 
 "ground in," using a grinding compound of emery or some 
 hard substance, so that the seat on both valve and port will be 
 symmetrical and perfectly smooth. 
 
 PROPELLER DRIVE 
 
 The method of driving the propeller depends upon the 
 running speed of the engine. The speed at which the propeller 
 may efficiently be driven is limited to a rather narrow range, 
 
 18 
 
varying ordinarily from 1100 to 1500 r.p.m. It has, however, 
 been found practical to operate especially designed and con- 
 structed propellers at speeds as high as 1800 r.p.m. This, how- 
 ever, is done at some sacrifice to efficiency. The enormous 
 centrifugal force developed by high speed rotation is of course 
 one of the main limiting factors, but the even more serious one 
 is the slippage and consequent efficiency drop occurring at high 
 speeds. Where the engine speeds remain below 1600 to 1800 
 r.p.m. the propeller will usually be driven by direct attachment 
 to the crank shaft itself, by means of a hub, keyed or shrunk on 
 and secured by lock nuts. 
 
 There is, however, a constantly increasing tendency toward 
 engines of higher speeds in order to take advantage of the 
 consequent reduction in weight per horse-power developed. 
 The output naturally is augmented as the speed increases and 
 if the weight of the engine can be maintained about constant, 
 or only slightly increasing, the advantage is readily apparent. 
 This tendency is becoming more and more prevalent and 
 makes necessary the geared down propeller drive. By employ- 
 ing a propeller drive shaft geared to the crank shaft, it is 
 perfectly possible to surmount the difficulty and maintain effi- 
 cient propeller speeds by properly regulating the gearing. At 
 the present time gearing has been so greatly improved that the 
 consequent drop in horse-power output, through its employ- 
 ment, is practically negligible as is the consequent increase of 
 weight which it causes. 
 
 The thrust of the propeller is transmitted through the 
 engine to the longerons of the fuselage. It is taken up by the 
 crank case from the crank shaft by a ball thrust bearing at the 
 propeller end of the shaft. 
 
 It is most important to keep the propeller lined up at all 
 times, otherwise severe and dangerous vibration will result. 
 The most common method of checking propeller allignment is 
 to measure from a fixed point on the engine to a certain point 
 
 19 
 
on the propeller surface, the propeller blade being in the ver- 
 tical position. Bring the other blade into the same position 
 and measure the corresponding distance. This should check 
 within 1/32" to 1/16". If the error is greater it can be coun- 
 teracted by means of the hub bolts. If propeller vibration is 
 noticed and lining does not correct it, change the propeller, as 
 propellers have been known to be inherently wrong and yet 
 appear to be as specified in every way. 
 
 MULTI-CYLINDER ARRANGEMENT 
 
 From the events of the four-stroke cycle it will be seen 
 that there is only one power application on a piston during the 
 four strokes. In other words, the power stroke must furnish 
 energy enough to carry the engine through three dead strokes 
 and also to perform useful work. Realizing this, it is simple 
 to see that the one cylinder engine will deliver power in a 
 very spasmodic manner. 
 
 It would be perfectly possible to build a one-cylinder 
 motor of enormous horse-power, but the explosions would be 
 so tremendous and occurring at such a distance apart, that not 
 only would the engine have to be enormously heavy, but vibra- 
 tion would be such that it would be utterly useless. 
 
 One great advantage of the electric motor is that power is 
 applied to the rotating shaft throughout its entire rotation. 
 Then why not break up the dead intervals of the one-cylinder 
 engine by utilizing several cylinders whose combined power 
 would approach a steady application instead of coming spas- 
 modically? This would have numerous advantages. Compar- 
 ing a one-cylinder engine to an engine of several cylinders, but 
 the same horse-power, it is easily seen that the power delivery 
 will be more constant, and terrific strains will be eliminated, 
 due to the more constant succession of power strokes. This 
 means that vibration will be reduced, weight of parts will be 
 
 20 
 
reduced and consequently internal friction, all of which will 
 tend to increase the useful work output of the engine. 
 
 With these thoughts in mind, it is clear why the one- 
 cylinder arrangement gave way to the two, and the two to the 
 four and six, and the four and six to the eight and twelve. 
 For naval aviation purposes four cylinders is the minimum 
 number used. Where fours and sixes are used the cylinders 
 are arranged vertically in a straight line and a crank shaft 
 constructed so that connecting rods from each cylinder may 
 be attached to each crank throw. In these engines the crank 
 shafts have as many throws as there are cylinders and are so 
 constructed that power is applied evenly throughout each revo- 
 lution. 
 
 If eight cylinders are to be used it is obvious that their 
 arrangement, vertically in a straight line, would necessitate a 
 very long crank shaft, and the engine would take up great 
 space. It is possible to obviate this by splitting the cylinders 
 into two sets and placing these sets, or banks as they are com- 
 monly termed, on an angle with each other. Such an engine 
 is called an eight-cylinder V-type engine because of the V angle 
 between banks. With this arrangement it is then seen that the 
 space occupied is much more compact. Also the necessity of a 
 very long crank shaft is overcome, and by regulating the angle 
 between banks, the ordinary four-cylinder crank shaft is used, 
 having t\vo connecting rods, one from each bank, fastened to 
 each crank pin. The same principles are applied to the twelve 
 cylinder engines, except that the banks consist of six cylinders 
 each and again, by regulating the angle between banks, the 
 six-cylinder crank shaft is used. The regulation of this angle 
 depends upon the firing interval desired. If the interval is to 
 be equal, the angle between banks must equal the firing interval. 
 If the angle is of any other value the firing intervals will be 
 unequal. 
 
 21 
 
COOLING 
 
 The combustion of the explosive mixture inside the cylin- 
 der of an aviation engine generates intense heat; this con- 
 tinued generation of heat would soon render the engine inop- 
 erative if the cylinders were not cooled in some way. There 
 are two ways of doing this, with air or with water. The prin- 
 ciple of both systems is to conduct the excess heat of combus- 
 tion rapidly enough away from the cylinder walls to prevent 
 damage by burning away the oil and causing the pistons to 
 seize. 
 
 Water Cooling: Heat is dissipated in a water-cooled 
 engine by surrounding the cylinder wall with another wall, and 
 by circulating water through the space in between the two. 
 The external wall is called the water jacket. Water jackets 
 around the cylinders can be formed in various ways. If the 
 cylinders are of cast iron or cast aluminum, the jacket is 
 usually cast integral with the cylinder. Sometimes the jacket 
 is made of sheet metal, brazed or welded to the cylinder. This 
 latter type of jacket is used when the cylinders are of steel, as 
 in the Liberty engine. Only a small quantity of water can be 
 carried in an airplane, hence the hot water which has just cooled 
 the cylinder must itself be cooled and used over again. 
 
 RADIATORS 
 
 The hot water from the water jacket is cooled by air in 
 much the same manner as an air-cooled engine cylinder, that 
 is, by radiation and conduction. The device for this purpose 
 is called a radiator, and consists of a series of very thin water 
 passages around which air can circulate. Circulation of air is 
 provided by the motion of the plane through the air. 
 
 WATER CIRCULATION 
 
 The water, in being used over again, is circulated through 
 the water jacket and then through the radiator. The direction 
 
 . 22 
 
of circulation is determined by the fact that heated water tends 
 to rise and cooled water to fall. Hence, the cooled water from 
 the radiator is introduced at the bottom of the water jacket, 
 and the hot water from the top of the water jacket is led off to 
 the top of the radiator. This natural tendency for heated 
 water to rise is sufficiently strong to cause an actual circula- 
 tion of water around the cooling system, provided the water 
 passages are large, and the system full of water. This is called 
 thermo-syphon circulation. It is customary on aviation en- 
 gines, however, to make the water circulation positive by 
 means of a pump acting in the direction of the thermo-syphon 
 action. By this means less \vater is required and the cylinder 
 temperature can be more closely controlled. 
 
 WATER PUMPS 
 
 The kind of water pump most commonly used is the centri- 
 fugal type, consisting of a rotating impeller or paddle wheel 
 in a casing. Water is led into the center of the impeller and 
 is thrown out to the edge by centrifugal force. The outlet is 
 at the rim of the casing. 
 
 OPERATION OF COOLING SYSTEM 
 
 The temperature of the water in the cooling system is an 
 excellent indication of the condition of the cooling, lubrication, 
 carburetion and ignition systems, as there are troubles which 
 can occur in all these systems which cause overheating. 
 Hence a thermometer of some kind with a dial on the cockpit 
 instrument board is used to indicate the water temperature. 
 Excessive water temperature should lead to an investigation 
 of its cause. 
 
 It is impossible to lay too much stress upon the importance 
 of this instrument. It is the pulse of the cooling system. The 
 pilot must be familiar with its proper recordings and should 
 train himself to pay particular attention to it at all times. If 
 
 23 
 
this is done trouble may very probably be remedied before it 
 becomes dangerous. The bulb of the water temperature meter 
 is usually located in the outlet header of the water system, and 
 indicates thr temperature of the water that is leaving the 
 cylinder jackets, which is the maximum temperature of the 
 water in the system. 
 
 LUBRICATION 
 
 Any internal combustion engine has a great many sliding 
 and bearing surfaces. Friction is ever present at these points 
 and must be minimized for efficient operation. Not only does 
 friction cause loss of useful power, but it also generates heat. 
 To minimize both these effects some good lubricant must be 
 used, so that an oil film may be established between sliding and 
 bearing surfaces. This metal to metal contact will be avoided 
 and friction consequently reduced. 
 
 In all naval aviation engines oiling is sent to the various 
 parts by pressure maintained by a pump usually of the rotary 
 gear type. The oil being under pressure is sent through tubes 
 or ducts to the various bearing points. 
 
 It may then be seen that oiling troubles may be detected in 
 two ways, by temperature and also by pressure. A gauge is 
 provided for recording both these. These are the pulses of the 
 oiling system and here again the pilot must observe the tem- 
 perature and pressure of the oil at all times. Sudden increases 
 or drops in either should be investigated at once. 
 
 Oil may be carried in the sump of the engine or in outside 
 reservoirs at a level above the oil pump. In the latter case 
 the engine is said to have a dry sump. This type is advan- 
 tageous for two reasons. The oil is well cooled by being cir- 
 culated through the outside reservoir and there is no danger 
 of oil from the sump flooding the cylinder when the machine 
 is at a heavy angle. There is a return pump provided to take 
 oil from the sump and return it to the reservoir. 
 
 24 
 
In the average pressure system oil is forced from the pump 
 through a strainer to the crank shaft, camshaft, pump and 
 magneto drive shaft bearings direct. However, oil must be 
 conveyed through passages drilled in the crank shaft to the 
 crank pin bearings on account of their rotation. From here 
 the cylinder walls, piston pin bearing, etc., may be lubricated 
 in two ways. Since the big end connecting rod bearings must 
 have clearance, oil will be forced out due to the pressure. This 
 will be beaten into a fine mist by the revolving crank shaft and 
 thrown upwards, lubricating cylinder walls, piston pin, etc. 
 This type of oiling is called Force Feed. In some engines this 
 is not considered positive enough. Accordingly a duct is run 
 from the big end connecting rod bearing, along the rod, to the 
 piston pin. This supplements the force feed system and is 
 called a Full Force Feed system. 
 
 Oil is transferred under pressure from a stationary bearing 
 to the inside of a rotating shaft by a hole in the shaft wnich 
 registers once every revolution with the supply lead to the 
 bearing. This method is used to carry the oil from the crank 
 shaft bearing into the hollow crank shaft and from the crank 
 pin to the connecting rod, and thence up the connecting rod 
 duct to the piston pin; this latter being in the full force feed 
 system. Only a small portion of the oil is actually consumed, 
 the rest returns to the sump, and thence to the reservoir, if the 
 sump is of the dry type, and is used over again. 
 
 Particular attention must be given to the oil temperature. 
 It must be moderate so that the oil may retain good lubricating 
 qualities. Here again is another advantage of the dry sump 
 since this system also serves to cool the oil. It is just as 
 necessary to watch oil pressure, which must be maintained 
 within certain limits for efficient lubrication. In most cases 
 there is a Pressure Relief Valve provided by which pressure 
 may be regulated or at least limited. This consists simply of a 
 valve held seated in some main oil passage by a spring set to 
 withstand a certain pressure. This limits maximum pressure, 
 
 25 
 
which is necessary to prevent flooding of the engine with too 
 much oil. The oil pressure meter must be carefully watched. 
 Very often serious accidents may be averted by paying atten- 
 tion to sudden pressure drops which are always an indication 
 of trouble. 
 
 Oil loses its body after being used, also it collects fine par- 
 ticles of metal from bearings, etc. It is therefore poor economy 
 to use oil too much. It should be changed often. More often 
 at first in a new motor, since the wear on bearings will be 
 greatest at first. When the motor is torn down all oil leads 
 should be carefully cleaned out to prevent collection of any- 
 thing which would tend to form obstructions. 
 
 CARBURETION 
 
 Carburetion is the process of saturating air with hydro- 
 carbon in the correct proportion for a combustible mixture. 
 The most important function which a carburetor has to perform 
 is to supply to the engine, under all conditions of load, speed 
 and throttle opening, a mixture of such proportions of gasoline 
 and air as will result in the most complete combustion and 
 maximum power. 
 
 It has been found that the correct mixture should consist 
 of approximately fifteen parts of air to one part of gasoline 
 by weight. 
 
 The Zenith carburetor is being widely used for aviation 
 work because of its simplicity, as mixture compensation is se- 
 cured by a compound nozzle arrangement that gives very good 
 results in practice. To understand the carburetor we will have 
 to consider, first,* the simple type of carburetor. 
 
 A simple carburetor consists of a single jet or nozzle 
 placed in the path of incoming air. The gasoline is fed to 
 this jet or nozzle by a float chamber. It is natural to suppose 
 that as the suction of the engine increases the flow of gasoline 
 and air will increase in the same proportion. This, however, 
 
 26 
 
is not the case. There is a law of liquid bodies which states 
 that the flow of gasoline from the jet increases under suction 
 faster than the flow of air, giving a mixture which grows 
 richer and richer as the engine speed increases. A mixture 
 containing much more gasoline at high speed than at low. It 
 is easily seen from this that the simple type of carburetor 
 would give very unsatisfactory results and could not be used. 
 The common method used to correct this defect is to attach 
 auxiliary air valves which add air and tend to dilute the mix- 
 ture as it gets too rich. These auxiliary air valves, however, 
 are very hard to gauge and, having delicate springs, get out of 
 order very easily, and are nothing more than a makeshift. 
 
 The Zenith system of compound nozzle depends upon the 
 compensating effect of one jet giving a leaner and leaner mix- 
 ture, as engine speeds increase, upon the jet of the simple car- 
 buretor as described above. To do this the principle of con- 
 stant flow is used. Accordingly a device allowing a fixed 
 amount of gasoline to flow by gravity into a well w r hich is open 
 to the air, is made use of. One jet may then be connected 
 direct to the float chamber. This is known as the main jet and 
 naturally gives a richer and richer mixture as engine speeds 
 increase. Another jet may now be placed around the main jet, 
 connecting with the atmospheric well. This is known as the 
 Cap Jet. The constant flow device (the compensator) then 
 delivers a steady rate of flow of gasoline per unit of time, and 
 as the suction of the motor increases more air is drawn in 
 while the amount of gasoline remains the same and the mix- 
 ture grows poorer and poorer. By combining these two types 
 of rich and poor mixture jets the Zenith compound nozzle was 
 evolved. 
 
 One jet counteracts the defects of the other, so that from 
 the starting of the engine to its highest speed there is a consant 
 ratio of air and gasoline to supply an efficient mixture. In 
 addition to the compound nozzle the Zenith is equipped with an 
 idling device. When the throttle is nearly closed the compound 
 
 27 
 
FIGURE 1 
 
 FIGURE 2 
 
 FIGURE 3 
 
 FIGURE 4 
 
 28 
 
PRIMING HOLE U 
 
 PRIMING TUBE J 
 
 BUTTERFLY T 
 
 SECONDARY 
 WELL P 
 
 CHOKE X 
 
 CAP JET M 
 
 MAIN JET O 
 
 Cross Section of 
 Zenith Carburetor 
 
 COMPENSATOR I 
 
 FIGURE 5 
 Explanation of preceding figures 1, 2, 3, 4, 5. 
 
 T. Butterfly valve (sometimes called throttle valve). 
 Float chamber. 
 
 Venturi (sometimes called choke). 
 Jet. (In Zenith Main Jet.) 
 Main well. 
 Compensator. 
 Cap jet. 
 
 Passage through which gasoline flows to main jet. 
 Passage through which gasoline flows to cap jet. 
 The arrows indicate the flow of air. 
 
 Figure 1 shows a simple type of carburetor, the jet G is placed 
 in the path of incoming air, the suction of the jet is created by 
 
 29 
 
 F. 
 X. 
 
 G. 
 J. 
 
 H. 
 E. 
 K. 
 
the Venturi X, the smallest internal diameter of which is located 
 at the opening of the jet. It has been explained that this type of 
 carburetor would supply an increasingly rich mixture as the suction 
 increased. The air valve shown in figure 2 was fitted in order to 
 admit air above the jet and not increase the suction on the jet. 
 This valve did not prove a success on aviation engines, for several 
 reasons. The Zenith uses the compound nozzle as shown in 
 figure 4. The main jet G supplies as mixture that grows richer 
 and richer as the speed increases, and a mixture that grows leaner 
 and leaner as the speed increases. 
 
 The action of the cap jet is shown in figure 3 as follows: 
 The compensator I, feeds gasoline into the main well J, which 
 is open to atmospheric pressure, suction on the cap jet H, would 
 draw this gasoline out of the main well J, but owing to the main 
 well being open to atmospheric pressure, the flow of gasoline 
 through the compensator I, would not increase, the suction on the 
 compensator being relieved by the air held in the top of the main 
 well. The mixture supplied by the cap jet would therefore grow 
 leaner and leaner as the speed increased. This compound jet main- 
 tains a constant mixture of gasoline and air at all speeds. 
 
 Figure 5 shows a cross section of a complete Zenith carburetor, 
 the butterfly valve T, is shown in the idling position, there being 
 no suction on the jets, the main well will fill with gasoline to the 
 level of the gasoline in the float chamber. The suction then comes 
 on the priming hole U, and gasoline will be drawn out of the 
 main well, through the priming tube J, this amount of gasoline 
 being regulated by the size of the hole in the secondary well P, 
 and the regulating screw O. 
 
 nozzle gives no gasoline, but as there is considerable suction at 
 the edge of the butterfly valve, gasoline is drawn through a 
 small hole drilled in the body of the carburetor and connected 
 to an idling jet which is submerged in the gasoline that is in the 
 well. 
 
 A carburetor adjusted to supply a properly proportioned 
 mixture at sea level will supply in increasingly rich mixture as 
 the machine mounts to higher altitudes, due to the difference in 
 temperature, density and quantity of oxygen in the air. To 
 overcome this an altitude adjustment is used. In the ordinary 
 Zenith this is simply a butterfly valve which may be opened by 
 
 30 
 
the pilot allowing more air to enter the top of the mixing cham- 
 ber, thus making up for the loss in density due to higher alti- 
 tudes. This adjustment does not interfere with the suction at 
 the jets to any extent, but simply admits more air. 
 
 The effect of altitude in carburetion is illustrated in the 
 following paragraphs taken from an article written by the 
 Zenith Carburetor Company: 
 
 "In regard to the necessity of changing jets in the Zenith 
 Carburetor in the higher altitudes above sea level, we have no 
 hard and fast rule governing the different sizes according to 
 variation in elevation. The Zenith Carburetor varies so greatly 
 from the air valve carburetor that the effect of altitude is very 
 much less with this type of carburetor, due to the surface of 
 the air valve, also the tension of the spring being very sensi- 
 tive to the reduced atmospheric pressure. For instance, we 
 have at sea level atmospheric pressure of 14.7 pounds per 
 square inch; at 5,000 ft., 12.18 pounds; at 8,000 ft., 10.87 
 pounds; at 10,000 ft., 9.96 pounds; at 12,000 ft., 9.31 pounds. 
 
 "It will be very readily seen, with this great reduction in at- 
 mospheric pressure action upon spring and valve, it would be 
 necessary to make this spring very much weaker, whereas in the 
 Zenith Carburetor we have no valves or springs regulating the 
 amount of air taken in. Therefore, very great differences in 
 altitude have very little effect on the actual operation of the 
 Zenith Carburetor. 
 
 "Just a little data on the effects of altitude in regard to the 
 gasoline motor developing its rated horse-power. 
 
 "Air consists of two gases oxygen and nitrogen in the 
 proportion of l/5th oxygen and 4/5th nitrogen by weight. 
 This proportion holds good all through the atmosphere from 
 the bottom to the top. Oxygen is the element that supports 
 combustion. Consequently, if we go to a higher altitude, where 
 the air pressure is less, a given volume of air will not weigh 
 as much as a similar volume at sea level. It will not contain 
 as much oxygen. 
 
 31 
 
"From this we see that a cylinder full of air at sea level 
 will contain a greater weight of oxygen than the same cylinder 
 on the top of a high mountain. 
 
 "Assuming the carburetor adjustment to be the best for 
 efficient running at sea level, with altitude valve closed, it will 
 be advisable to start opening the altitude valve at about 2,500 
 feet elevation and keeping it as far open as possible without 
 reducing the engine r. p. m. 
 
 "Extensive test have shown that above 5,000 feet eleva- 
 tion change in engine power will be negligible, but that con- 
 sumption of fuel will be reduced from 8 per cent, to 10 per cent, 
 by operating the engine with the altitude valve open." 
 
 There is another general type of carburetor coming more 
 and more into prominence known as the multiple jet type. 
 Under this heading come the Miller and the Master. A num- 
 ber of jets are set in a straight line, and so arranged that the 
 size of the jets increase progressively. The throttle valve is 
 of the barrel type, which more nearly approximates the action 
 of a variable venturi. On opening the throttle to speed up, the 
 jets are uncovered progressively. In this way a very strong 
 venturi action is centered at slow speeds over one or two 
 small jets and as the speed is increased this action is decreased. 
 The additional gas being provided by the remaining jets as 
 suction reaches them. Carburetors of this type are simple in 
 construction and easily maintained once they are regulated. 
 This can be done only by a careful study of the engine demands 
 and adaptation of suitable jets in accordance. One regulated 
 they are singularly free from adjustments. 
 
 The Stromberg Company has recently developed a car- 
 buretor for aviation purposes which, on recent tests, has given 
 excellent results. 
 
 The Stromberg carburetor maintains the proper mixture 
 by what is known as an air-bled jet. Gasoline leaves the float 
 chamber, passes the point of a high-speed adjustment needle, 
 and enters a vertical channel or well. Air is taken into this 
 
 32 
 
channel through the air-bleeder, or air adjustment. This air 
 discharges into the gasoline channel through small holes and 
 beats up the gasoline into a fine spray. This then enters 
 through a number of jets into the high velocity air stream of 
 a small venturi. There is a second or large venturi provided 
 through which the mixture next passes. Since good excellera- 
 tion requires a temporary enrichment, there is a reserve cham- 
 ber or excellerating well provided which is concentric to and 
 communicates with the vertical channel mentioned above. 
 With the motor idling or slowing down, this well fills with 
 gasoline and whenever the venturi suction is increased by open- 
 ing the throttle, the level in the well goes down and the gaso- 
 line thus displaced adds to the amount entering the small 
 venturi. 
 
 The carburetor is also provided with an idling device. In 
 the center of the vertical channel, there is located a long tube 
 which extends up the side of the carburetor, and has an en- 
 trance to the mixing chamber through a small hole at the level 
 of the butterfly valve; when the throttle is closed, or nearly 
 closed, gasoline enters through this small hole. The proper 
 mixture is maintained by regulating the admission of air into 
 the idling tube by an idling adjustment screw. This idling ad- 
 justment does not work after the throttle has been opened, so 
 that the engine runs above idling speed. 
 
 There is still another type of carburetor which furnishes 
 the proper mixture at all speeds by means of a variable ven- 
 turi. Many models have been constructed using this idea but 
 they are to the greatest extent still in experimental stages and 
 so far are a great ways from perfection. The adoption of 
 this principle would be ideal and there are several corburetors 
 which attempt to approximate it in various ways. 
 
 EFFECTS OF IMPROPER CARBURETION 
 
 As already stated the problem of carburetion is to main- 
 tain the proper mixture at all engine speeds. There are numer- 
 
 33 
 
ous effects which will give indications of an improper mixture. 
 First let us consider the effects of a lean mixture; that is, a 
 mixture in which there is too little gasoline per unit of air. 
 
 The lean mixture will, in the majority of cases, be made 
 evident by back-firing or spitting back of the carburetor. The 
 cause of this is that the mixture, containing too little volatile 
 matter, will be slow burning, and some of it will still be burn- 
 ing when the intake valve opens on the next succeeding stroke. 
 Naturally this will cause ignition of the gases in the intake 
 manifold and a back-fire will result. This is very dangerous 
 as fire is likely to result if the carburetor is not placed where 
 it will be away from any gasoline drip which may have col- 
 lected. A lean mixture being slow burning will expose more 
 cylinder wall to heat than a proper mixture, and, therefore, it is 
 said that overheating will result. There will be a tendency 
 toward this, but it is generally conceded that this effect is 
 neutralized to a great extent by the cooling effect of the addi- 
 tional air present in the mixture. Naturally an engine running 
 on too lean a mixture will not develop the proper power. 
 
 A rich mixture is also slow burning. It, however, does 
 not cause a back-fire but will cause an after-fire. It is naturally 
 a heavier, more homogeneous gas than a lean mixture and 
 consequently none of it is left in the cylinder after the exhaust 
 stroke. Therefore, back-fire cannot occur, but a loud exhaust 
 or after-fire will result. 
 
 Also, on account of slow burning, overheating will result, 
 since more cylinder wall than should be is exposed to the burn- 
 ing gases and the cooling system will be over-taxed. Due to the 
 greater amount of carbon present in the mixture, and its in- 
 complete combustion, the formation of carbon will proceed 
 more rapidly with its consequent detrimental results. A rich 
 mixture will also result in loss of power. 
 
 An expert can tell by the color of the exhaust flame the 
 exact condition of the carburetion system. The proper flame 
 is almost- an invisible blue, while a yellowish flame indicates a 
 
 34 
 
lean mixture and a red flame, accompanied in bad cases by 
 black smoke, a rich mixture. 
 
 ELECTRICITY AND MAGNETISM 
 
 Units : 
 
 Volt = Unit of pressure. 
 
 Amperes = Rate of flow. 
 
 Ohm == Unit of resistance. 
 
 Watt = Unit of power (Volts X amperes). 
 
 Resistance is the opposition that any material offers to 
 the flow of an electric current. 
 
 A conductor is a metallic substance of low resistance that 
 is used to conduct an electric current; viz: a coil of copper 
 wire. 
 
 An insulator (non-conductor) dielectric any substance of 
 such high resistance that practically no current can flow through 
 it. (Glass, porcelain, rubber, etc.) 
 
 Magnetism is the invisible field of forces operating be- 
 tween the poles of a magnet, and in circular rings about a 
 wire through which a current is flowing. This magnetic field 
 exists in the form of lines of force, or flux. The permanent 
 magnet is usually made in the form of a horse shoe, and is 
 always used to furnish the magnetic field in a magneto. In a 
 generator and in the battery type ignition, an electro magnet 
 is used. This is not a permanent magnet, and only sets up 
 a magnetic field as long as electricity is flowing through the 
 conductor that is wound around its soft iron core. 
 
 INDUCTION 
 
 Induction may be taken to mean, in simple words and 
 for present purposes, causing an electric current to exist. This 
 may be accomplished in three ways : 
 
 1. Passing a conductor through a magnetic field or lines of 
 
 35 
 
force, thereby causing the conductor to cut the field and in- 
 ducing a voltage in it and current, if a closed circuit. That 
 is, having a stationery field and a moving conductor. 
 
 2. Reversing the above condition, that is, having a station- 
 ary conductor, but a movable field. 
 
 3. Having both conductor and field stationary and induc- 
 ing a current by changing field strength, that is, causing a 
 change in the value of the flux. 
 
 IGNITION 
 
 After the gas has been compressed by the compression 
 stroke, it must be ignited in order to furnish the expansion 
 necessary to force the pistom down for the power stroke. A 
 spark plug consisting of two electrodes, separated by an in- 
 sulating material, is screwed into the combustion chamber of 
 the cylinder. The two electrodes are separated at their ends 
 or points by an air gap, and by causing an electric spark 
 to jump this gap, the compressed gas is ignited. The electric 
 current necessary to jump across the spark plug gap is fur- 
 nished by the ignition system, which can be of the magneto 
 or battery type. 
 
 The ordinary current furnished by a battery or generator 
 is not of sufficient voltage or pressure to jump across the gap 
 of the spark plug, and in order to raise the voltage of the 
 battery or generator, an induction coil is incorporated in the 
 ignition system, and supplies the high voltage current nec- 
 essary to jump the spark plug gap. 
 
 If a conductor is coiled about a soft iron core, and cur- 
 rent is caused to flow through the coil, the core will become 
 a magnet, thereby causing a magnetic field to be established. 
 The moment current ceases to flow in the coil the core ceases 
 to be a magnet and consequently its magnetic field collapses. 
 Now, if a second coil be wrapped about this first, the collapse 
 of the magnetic field, caused by breaking the circuit of the 
 
 36 
 
first coil, will induce a current in the second. This is the 
 principal of the induction coil. The first coil which causes 
 the core to be magnetized and de-magnetized, is called in the 
 primary. The second or out coil is the secondary. Both are 
 wound on the core, the secondary over the primary. 
 
 The primary coil consists of a comparatively small num- 
 ber of turns of coarse wire while the secondary contains a 
 large number of turns of very fine wire. The desired result 
 is to obtain high voltage or high pressure which will be capa- 
 ble of breaking down the resistance of the spark plug gap. 
 Consequently, the induced or secondary current must be of high 
 voltage or high tension. As it is impossible to get something 
 from nothing the power or \vattage of both primary and secon- 
 dary circuits must be theoretically the same. Consequently, the 
 secondary must be of low current value in order to allow the 
 higher voltage value since wattage must remain constant. 
 
 It can then be understood why fine wire is used for sec- 
 ondary purposes. Simply because it will not be conductive 
 to heavy amperage; in fact will make it impossible for heavy 
 amperage to exist and the result, since wattage must be the 
 same as in the primary, will be high voltage value. 
 
 Since the induced voltage is directly proportional to the 
 ratio of the number of turns in the secondary coil to the 
 number of turns in the primary, it may be easily seen why 
 the secondary will consist of a large number of turns; bear- 
 ing in mind that the desired result is high voltage. 
 
 Breaker Mechanism: 
 
 The intensity of induced voltage will also be greatly de- 
 pendent upon the rapidity with which the secondary coil is 
 cut by the collapsing field. That is, maximum voltage will be 
 dependent upon maximum rate of change of flux. The most 
 effective method of obtaining this result is to suddenly in- 
 terrupt the flow of primary current, thus stopping the genera- 
 tion of lines of force by it, and changing instantaneously 
 
 37 
 
the number of lines of force through the secondary from a 
 maximum to zero. The device which interrupts the primary 
 circuit is the Breaker Mechanism, consisting of two breaker 
 points, one stationary the other held in contact by a lever 
 and spring. The cam acts on the lever causing these points 
 to separate and break the primary circuit. 
 
 Condenser : 
 
 Current is flowing around the primary circuit at the 
 moment of interruption by the breaker points, and due to its 
 own inertia, it tends to keep on flowing and jump across the 
 air gap created by the separation of the breaker points. If 
 no provision were made to stop this condition, the induced 
 or secondary voltage would not be as intense as possible. The 
 reason for this would be that due to the leakage across the 
 points the collapse of the magnetic field would not be abrupt. 
 It has been pointed out that the more rapid the collapse, the 
 more intense the ^induced voltage ; hence this leakage must be 
 stopped. Not only will the induced voltage be poor, but the 
 breaker points will become badly pitted due to the arcing 
 across the air gap created. This would make it impossible 
 to keep the points clean, well surfaced and at correct adjust- 
 ment, all of which would be decidedly detrimental. To over- 
 come these defects a condenser is connected around the breaker 
 points. A condenser is composed of alternate layers of a con- 
 ductor and a dielectric, very often tin foil being used for the 
 former and mica for the latter. 
 
 The alternate layers of the conductor are connected to 
 opposite terminals of the device. Hence there is no path for 
 current through the condenser, but it acts as a reservoir. When 
 the breaker points separate, the current flows into the con- 
 denser instead of arcing across the points. When the con- 
 denser is fully charged it rapidly discharges in the reverse 
 direction, thereby causing a sudden reversal of magnetic flux, 
 and this condition continues, producing an oscillatory current 
 
 38 
 
of very high frequency until the current value becomes so 
 reduced that the action must cease. This oscillatory discharge 
 has its effect on the secondary induction, the result being a 
 prolonged spark assisting in overcoming the resistance of the 
 spark plug gap and insuring better ignition. At times some 
 of the dielectric substance will be punctured thus reducing the 
 capacity of the condenser and making it necessary for part of 
 the current to jump across the breaker points. Where pitted 
 points are found the operator can be practically positive that 
 the condenser is faulty. If, however, the condenser becomes 
 entirely burned out, the result will be a short circuiting of 
 the breaker points and no interruption of the primary, result- 
 ing in no ignition. 
 
 Breaker Point Adjustment: 
 
 In every ignition system there is a certain maximum 
 distance of opening for which the breaker points are designed. 
 They must be kept in adjustment so that the opening will al- 
 ways be correct. Suppose the opening prescribed is to be 
 0.020" and the adjustment is faulty so that the opening per- 
 mitted is above the net amount. Naturally it will take longer 
 for the points to return to contact. This will result in a 
 considerable lag at high engine speeds, and it is common to 
 have this condition drag out to such an extent that ignition 
 will fail for as much as one complete revolution. The re- 
 sult, then, of too great a gap, will be faulty ignition and con- 
 sequently misfiring. If the opening is below the prescribed 
 amount, the resistance of the air gap will reach a point where 
 it will be below the resistance of the primary coil. Then 
 when the condenser discharges, instead of going through the 
 coil, the current will arc across the points, the result being 
 the same as given by a faulty condenser. Again the result 
 will be faulty ignition. 
 
 It may then be seen that correct breaker point adjustment 
 is imperative for proper engine running. 
 
 39 
 
Distributor : 
 
 The spark will jump across the spark plug gap when 
 the current induced in the secondary is at a maximum value, 
 in other words, when the breaker mechanism interrupts the 
 primary current. Hence, the breaker mechanism must be 
 timed to the engine so that the spark will occur at the proper 
 time. If only one cylinder is to be ignited, the secondary 
 wire can be led directly to the spark plug. However, when 
 more than one cylinder is used, a device must be introduced 
 to direct the high tension secondary current to the proper 
 cylinder. This device is called a distributor, and consists of 
 a rotating arm which touches one contact for each cylinder 
 in succession. A wire leads from each contact to its cylinder. 
 Hence, when the primary circuit is broken, a spark will be 
 flashed in the cylinder with whose segment the distributor arm 
 is making contact. 
 
 Ground : 
 
 In order to simplify wiring, one end of both the primary 
 and secondary circuits is attached to some metal part of the 
 engine. Thus the metal of the engine serves as one wire of 
 the circuit, and is known as the "ground." 
 
 Primary Circuit: 
 
 The primary circuit consists of a source of current, for 
 example, a storage battery, with one terminal wired to the 
 ground, the other terminal leads the current to the primary 
 windings of the induction coil; from the coil the current goes 
 through the breaker mechanism and then to the ground; the 
 condenser is connected around the breaker mechanism. 
 
 Secondary Circuit: 
 
 One end of the secondary coil is attached to the ground; 
 the other ends conducts the high tension current to the dis- 
 tributor arm; from there it goes to the spark plug as deter- 
 
 40 
 
mined by the proper distributor segment jumps across the gap, 
 to the ground. 
 
 MAGNETOS 
 
 A magneto contains all the elements of the ignition system 
 previously described, and has the same primary and secondary 
 circuits. It differs, however, in that it generates its own 
 primary current, again by the principle of induction. There are 
 two main methods of doing this. In both cases lines of force are 
 furnished by permanent magnets. The first type of magneto 
 to be discussed is that in which the charge in the number of 
 lines of forms through the coils is accomplished by rotating 
 the coils in the magnetic field created by the permanent 
 magnets. The intensity of the primary current induced in this 
 case depends to a great extent on the rate of change of flux, 
 which varies with the speed of rotation of the coils. The 
 coils are wound on a rotating member called the armature, 
 and the momentary intensity of the current depends on the posi- 
 tion of the armature, relative to the permanent magnets. 
 
 The armature used is of the shuttle type, a section of it 
 being roughly that of the capital letter I. The vertical part 
 of the shuttel then may also perform the function of a core 
 and the coils are wound about it, the primary first, then the 
 secondary. Magnetic lines of force follow the path of least 
 resistance, and it is obvious that there will be two points per 
 revolution of the shuttle where the lines of force passing- 
 through the core will change in direction. During the reversal 
 of flux, there will be a point if highest primary induction, 
 which, if utilized by opening the breaker points, will cause 
 maximum secondary induction. It may be seen that with this 
 type of magneto it is possible to obtain two sparks per revo- 
 lution of the shuttle. 
 
 Magnetos of this character are classified as revolving 
 shuttle type, and among them are the Bosch and Berling. 
 
 41 
 
DIXIE MAGNETO 
 
 The Dixie magneto operates on a principle entirely dif- 
 ferent from the rotating shuttle type. The magnets and wind- 
 ings in the Dixie are both stationary, and the only rotating 
 member is the rotary pole structure. 
 
 The rotary pole structure is an extension of the per- 
 manent magnets, and it rotates across the face of the field 
 pole structure. The primary and secondary coils are wound 
 around a core which is mounted on top of the field pole 
 structure in such a manner as to form a path for the magnetic 
 flux as it flows from the rotary poles. The rotary pole structure 
 having two extensions of the north, and two of the south, 
 arranged alternately, gives four reversals of flux through the 
 core of the windings every revolution of the rotary pole 
 structure. Consequently, there would be four inductions per 
 revolution, and one spark per induction. This is a decided 
 advantage over the rotary shuttle type which gives two sparks 
 per revolution, and has to rotate twice as fast to do the 
 same work. 
 
 From the above, it can be seen that the breaker mechan- 
 ism would have to open and close the primary circuit four 
 times per revolution; and the Dixie would be timed to rotate 
 one-half the speed of a Bosch or Berling on the same engine. 
 
 Referring to the drawing on page 43, it can be seen in 
 figure 1, that the rotary pole structure A, is in the position 
 of maximum flux flow, and that the magnetic flux is flowing 
 from the north rotating pole through the field pole structure 
 C, thence through the field pole D, and back into the south 
 rotating pole. It can be seen that a quarter revolution of 
 the rotary pole structure A, will give a complete reversal of the 
 magnetic flux, because the polarity would change from south 
 to north on one side and north to south on the other side. 
 Figure No. 2 shows a complete reversal of flux flow which 
 was brought about by a quarter revolution of the rotary pole 
 
 42 
 
DIXIE- MA6NE.TO 
 
 KEY- 
 
 A- ROTARY POLE STRUCTURE 1 - 
 
 D- fiE.1.0 CORE I- 
 
 E _p RlM flY. wviNOiNGS V* 
 
 F-SECOMOARY - N 
 
 6 - CONDENSER 
 
 H-BRERKER MCCHflNiSM F , 62 . 
 
 LEVER 
 K-CONTflCTS 
 
 l_-SWrTCM 
 
 43 
 
structure A. As it is this sudden reversal of flux that causes 
 the induction of current in the winding, and gives the spark. 
 Four of these reversals coming every revolution of the rotary 
 pole structure, will give off four sparks. It has been ex- 
 plained, in preceding chapters, that the primary circuit must 
 be interrupted for every reversal of flux or induction, and in 
 the Dixie magneto, this is provided for by a cam having four 
 lobes, and rotating at the same speed as the rotary pole struc- 
 ture. The windings, condenser, breaker mechanism, distrib- 
 utor, etc., are clearly shown in the drawing, a study of which 
 will enable the reader to clearly understand the Dixie principle. 
 
 TIMING 
 
 Valve Timing: It has been pointed out that there must 
 be certain valve action during certain piston strokes, and that 
 the valve action is controlled by the cam shaft which neces- 
 sarily must turn at half crank shaft speed. It is further neces- 
 sary to conform to the manufacturers' standards for exact 
 points of valve opening and closing. The average engine used 
 in naval aviation will conform within very close limits to the 
 following valve timing: 
 
 Intake Valve open TDC 15 Past TDC 
 
 Intake Valve closed 35 past BDC 50 Past BDC 
 
 Exhaust Valve open 50 before BDC 35 Before BDC 
 
 Exhaust Valve closed ....TDC 15 Past TDC 
 
 From this it will be seen that the following may be assumed 
 a good average chart for valve operation : 
 
 Intake open 10 Past TDC 
 
 Intake close 45 Past BDC 
 
 Exhaust open 50 Before BDC 
 
 Exhaust close 10 Past TDC 
 
 This may then be used for the ensuing discussion. It will 
 be noted that valves very seldom open or close on dead centers. 
 The distance by which a valve opens or closes before or after a 
 
 44 
 
dead center is usually measured as given, in degrees of crank 
 shaft rotation. It may also be measured, and is occasionally, 
 in linear distance of piston travel. 
 
 The intake valve is allowed to remain open after the piston 
 has passed bottom center, in order that a maximum charge of 
 gas may be drawn into the cylinder. The piston moving down 
 in the cylinder displaces space faster than the restricted area of 
 the intake port can allow it to be relieved, and even though 
 the piston has passed bottom center, there is still some vacuum 
 in the cylinder, and this vacuum will continue to draw in gas 
 as long as it exists and the intake valve is kept open until this 
 vacuum is completely relieved. 
 
 From the closing of the intake to the opening of the ex- 
 haust there can be no valve action, since compression and power 
 must take place and both valves must be kept closed during 
 compression and power. The exhaust valve opens early, or 
 before BDC, primarily to insure complete scavenging. At 50 
 before BDC the angularity of the connecting rod is so small 
 that any additional work given by expanding gases would be 
 slight. It is then better to utilize the expansion left in the 
 gases at this part of the stroke to aid scavenging, thereby insur- 
 ing its being more complete and relieving the piston of part of 
 the work on the exhaust stroke. The exhaust valve is allowed 
 to remain open until after TDC simply again to insure com- 
 plete scavenging. 
 
 The intake valve opens at a point which will allow equaliza- 
 tion of pressure in the cylinder. 
 
 It will then be seen that it is absolutely necessary to time 
 the valves so that their openings and closings will be exactly 
 in accordance with the manufacturers' specifications, since 
 these are given for best engine running results. 
 
 In order to time the cam shaft, and thereby the valves on 
 an engine having one cam shaft on which both exhaust and 
 
 45 
 
intake cams are placed, it is necessary to accomplish the fol- 
 lowing things : 
 
 (1) Determine the proper direction of rotation of the 
 engine. 
 
 This is best done by determining rotation to procure open- 
 ing of the intake at about the point of exhaust closing. It 
 may also be accomplished by determining the proper direction 
 of rotation of water pump or propeller. In these cases it is 
 necessary to take gear drives into consideration. 
 
 (2) Adjust the Valve clearance. 
 
 This must be done when the cam follower is on the low 
 part or heel of the cam so that the valves will be finally seated. 
 Such a condition will be sure to exist at about TDC of com- 
 pression stroke. This position may be approximated by turn- 
 ing the engine in correct direction to the point of closing of the 
 intake valve, then turning approximately half a revolution 
 more. 
 
 (3) Intake valve of No. 1 cylinder just opening. 
 
 This will bring the cam shaft into its proper position or 
 timing. 
 
 (4) Disconnect cam shaft from crank shaft. 
 
 Since the cam shaft is in its proper position it must not be 
 moved further. 
 
 (5) Place piston of No. 1 cylinder on Top Dead Center 
 and number of degrees after TDC as specified by tlic 
 manufacturer of intake valve to open. 
 
 This will bring piston to point for intake valve opening. 
 
 (6) Connect cam shaft to crank shaft. 
 
 (7) Check Timing very carefully. 
 
 For quick work very often the valve clearance is adjusted 
 for timing purposes on No. 1 cylinder only. If this method is 
 
 46 
 
employed, the clearance on the remaining valves must be set 
 and checked after timing. 
 
 It may then be seen that valve timing consists merely of 
 making an intake valve function when the piston is at the 
 proper position for such functioning to occur. Timing may be 
 done on either opening or closing of either valve, but it is 
 common pactice to use intake opening. 
 
 If there is only one cam shaft it is necessary to time on 
 one valve only. If there are more than one cam shaft, it is 
 necessary to time each cam shaft separately. 
 
 The angular travel of the crank shaft may be found by 
 means of a timing disk which is fastened to the crank shaft. 
 This is simply a disk graduated in degrees. 
 
 If, as may possibly be the case, the ignition system is 
 properly timed to an engine during valve timing, it is necessary 
 to be careful of the Top Dead Center used. Obviously, spark 
 must occur at or near TDC of compression, when both valves 
 must be tight closed. 
 Spark Advance and Retard: 
 
 In order to obtain maximum power, combustion should be 
 complete and, therefore, maximum pressure generated, at top 
 dead center. As a definite time elapses between the flashing 
 of the spark and the completion of combustion, the spark must 
 occur before top dead center, and the faster the engines run 
 the further in advance of dead center it must occur. If com- 
 bustion, due to a late spark, were completed after top dead 
 center, all power would not be extracted from the gases when 
 the exhaust valve opens, and overheating would result. If the 
 engine is turning over slowly, the spark must be retarded, or, 
 in other words, must occur later in the cycle, or the point of 
 maximum pressure will occur before top dead center, and the 
 crankshaft will receive an impulse to turn in the wrong direc- 
 tion, giving rise to a knock. If this occurred while, cranking 
 the engine, it would cause a back-kick. Hence the spark must 
 be retarded when cranking. This variation in the time of oc- 
 
 47 
 
currence of the spark is obtained by causing the cam to open 
 the circuit breaker points earlier or later. 
 
 This is accomplished by moving- the advance retard lever 
 in the same direction as the rotation of the magneto shaft to 
 obtain retarded spark and in the opposite direction to rotation 
 to obtain advanced spark. 
 
 Magneto Timing : 
 
 Since there are two positions in which the magneto may 
 be set, viz., advanced and retarded, it may readily be seen that 
 there may be two methods of timing, Advanced or Retarded. 
 
 Advanced Position: 
 
 (1) Determine direction of rotation of engine. As given 
 
 under valve timing. 
 
 (2) Determine direction of rotation of magneto. Usually 
 
 indicated by an arrow- stamped on the oil cup at 
 the driving end. 
 
 (3) Place piston of No. 1 cylinder at top dead center of 
 
 compression stroke and number of degrees before 
 TDC as specified by the manufacturer for ad- 
 vanced spark to occur. This is usually from 20 
 to 30. This puts the piston in position for spark- 
 to occur. 
 
 (4) Fully advance the magneto. 
 
 (5) Turn distributor brush to No. 1 segment. 
 
 (6) Turn magneto shaft until points are just breaking. 
 
 This places magneto in position ready to give 
 spark. 
 
 (7) Connect magneto to engine. 
 
 (8) Find firing order of engine by watching any succes- 
 
 sive valve operation. 
 
 (9) Connect distributor segments in accordance with firing 
 
 order. 
 (10) Check up timing. 
 
 48 
 
Retarded position: 
 
 The same as advanced method, except for the following: 
 In No. 3 place piston of No. 1 cylinder at TDC of compression 
 stroke. It is always safe to assume retarded spark as occurring 
 here. If the manufacturer specifies differently follow specifica- 
 tions. Some engines have retarded spark occurring a few 
 degrees after TDC. In No. 4 fully retard the magneto, other- 
 wise follow- the advanced method. The advanced method 
 should be used whenever possible. Only use the retarded 
 method when there is not sufficient data to enable the use of 
 the advanced method. 
 
 Note. Where two or more magnetos are used they must 
 be timed separately and so as to break at exactly the same in- 
 stant. If they are not so synchronized the effect will be that 
 of only one magneto. 
 
 EMERGENCY REPAIRS 
 
 It sometimes becomes necessary to make repairs of a tem- 
 porary nature, in order to keep an engine running. This is 
 especially true of long flights. In order to make repairs quickly 
 and intelligently, the operator must familiarize himself with 
 the propulsion plant of the flying-boat or plane he is operating. 
 
 A complete kit of tools and spares must be carried, and 
 the operator should inspect this kit carefully before starting 
 on a long flight. 
 
 When in flight the operator should pay particular atten- 
 tion to the various gauges, tachometer, oil and water tempera- 
 ture gauges, oil pressure gauge, and ampere meter. These in- 
 struments indicate at all times the working condition of the 
 engine, and a sudden change indicated on one of these gauges 
 is invariably an indication of trouble. Water-hose connections 
 sometimes burst or get loose. This results in a loss of water 
 and overheating of the engine, and would be indicated by the 
 
 49 
 
water-temperature meter showing a sudden increase of tem- 
 perature. Repairs can be made by fitting a new hose connec- 
 tion or binding the broken one with friction tape. As the 
 water has all escaped through the broken connection it becomes 
 necessary to use sea water. Sea water can be used in an emer- 
 gency of this kind in order to get back to the base or station, 
 and the cooling system should be thoroughly flushed with fresh 
 water as soon as possible. 
 
 Broken water jackets can be repaired on some engines 
 by plugging the inlet and outlet water pipes of the cylinder and 
 disconnecting the spark plug wires. This puts the damaged 
 cylinder out of service, and as it could not fire it would need 
 no water circulation. 
 
 On the Liberty engine using Delco ignition, it may become 
 necessary to start two or more engines with one battery. This 
 may happen with one of the large flying boats having two or 
 more engines, and is brought about by a battery becoming ex- 
 hausted or broken. In a case of this kind, two or more engines 
 can be started by connecting one good battery to the first engine 
 to be started, and starting same. Speed this engine up to 
 700 r. p. m. and throw back switches on. The battery generator 
 will then charge and the battery can be disconnected and used 
 in the same manner for starting other engines. 
 
 Temporary repairs to broken gasoline pipes can be made 
 by wrapping with tape or by slipping rubber tubing over each 
 broken end (this rubber tubing is usually carried in the kit). 
 
 50 
 
Valve timing 
 
 ENGINE CHARACTERISTICS 
 
 LIBERTY 12 
 
 12 Cylinders Vee type angle between cylinder banks 45. 
 
 Bore 5 inches. 
 
 Stroke 7 inches. 
 
 Cooling Water circulated by a high speed centrifugal pump. 
 
 Lubrication Force feed dry sump external oil reservoirs. Ca- 
 pacity, 13 American gallons. 
 
 Carburetion2 Zenith Duplex model U. S. 52. 
 
 Ignition Delco battery type. 
 
 Idling speed 650 to 800 r.p.m. 
 
 Intake opens 10 PTC. 
 Jntake closes 45 PBC. 
 Exhaust opens 50 BBC. 
 Exhaust closes 10 PTC. 
 
 Spark full advance Occurs 30 BTC. 
 
 Spark full retard Occurs 10 PTC. 
 
 Total spark movement 40 
 
 Spark plug gap .017" 
 
 Conditions for best resultsWater at outlet 170 Fahr. (Water 
 at outlet not to exceed 200 Fahr.) 
 
 Oil temperature desired 130 Fahr. (Sometimes goes to 150 
 Fahr.) 
 
 Oil pressure Varies between 20 Ibs. and 50 Ibs. 
 
 Generator charging rate With fully charged battery 1.5 to 3 
 amperes. 
 
 Firing order 1L-6R-5L-2R-3L-4R-6L-1R-2L-5R-4L-3R. 
 
 Vah-e clearance- I^e .014;; to .016;;. 
 I Exhaust .019" to .021". 
 Breaker gap All contacts .010" to .013". 
 Spark plug gapQ.17". 
 
 51 
 
THE LIBERTY ENGINE MODEL A 
 
 Timing gear end. Showing ignition heads, generator, cam 
 shaft drive, water pump and oil pump assembly. 
 
 52 
 
One of the chief characteristics of the Liberty engine is 
 the use of a 45 angle between banks. With the ordinary 
 twelve cylinders having an equal firing interval, the angle 
 used is 60. By decreasing this angle the resistance offered 
 by the engine in flight is naturally decreased. This is a very 
 important factor, particularly where the engine is incorporated 
 in the fuselage itself. The use of the smaller angle also makes 
 possible a more rigid construction, and better reinforcement 
 of the crank case. By the use of the consequent unequal fir- 
 ing interval of 45-75 the resultant sympathetic vibration 
 produced approximates 0. In any engine with an even firing 
 interval this vibration is foumi to a much greater extent and 
 as vibration is detrimental to the molecular construction of 
 the metals used, it may be seen the additional advantage 
 derived. To illustrate this point more clearly : a body of troops 
 marching across a bridge use "route step." If they were 
 allowed to march "in step" there would be serious danger 
 of collapse of the bridge, because of the resultant sympathetic 
 vibration. 
 
 The construction of the cylinders of the Liberty engine 
 follow to a certain extent the methods used by the Mercedes, 
 Benz, and other foreign manufacturers. The cylinder sleeve 
 itself is machined from a steel forging, the valve cages are 
 welded on, and the water jackets, which are of pressed steel, 
 are welded to this assembly. The cylinder itself is forged 
 by a unique process developed by the Ford Motor Company 
 a piece of steel, resembling a section of boiler tubing, is so 
 forged by means of steam presses that the finished product 
 is sealed at the top upset to provide the semi-spherical combus- 
 tion chamber, and have a metal ring providing the flange for 
 attachment to the crank case. By the use of this process the 
 expense of manufacture was greatly diminished over any 
 method heretofore used, and it was possible to turn out well 
 over two thousand forgings a day. This rough forging weighs 
 approximately fifty-eight pounds, while the finished cylinder, 
 
 53 
 
P o 
 
 1 
 
 HH CJD 
 
 J = 
 
 >< 'bn 
 ^ o 
 
 W " 
 
 54 
 
including, valves and valve springs, weighs only approximately 
 twenty pounds. From this it is possible to obtain some realiza- 
 tion of the machining done. 
 
 The cylinder extends considerably below the holding down 
 flange, giving increased strength to the assembly. The in- 
 formation of the combustion chamber is hemispherical with 
 the valves and spark plugs located symmetrically in the head. 
 The cylinder is upset at the combustion chamber, so that am- 
 ple clearance may be afforded for the large valves used. The 
 outside of the cylinder is flanged, so that additional cooling 
 surface is provided. 
 
 On account of the high compression used, it is necessary 
 to provide extremely efficient cooling. This is done by the 
 use of a pump of large capacity (one hundred gallons per 
 minute at maximum speed). Also the water enters the jackets 
 at the side, causing a swirling rapid circulation. It also flows 
 freely over the combustion chamber and around the valves. 
 From the top of the jackets it enters jackets surrounding 
 the intake manifolds, so that the incoming gases are heated. 
 From these manifolds it passes through the main water heater, 
 back to the radiator. 
 
 The cam shafts are of the over head type of special and 
 improved design, being well lubricated and yet practically oil 
 tight. They are driven by tower shafts, which derive their 
 motion from timing gears in the crank case. 
 
 The lubrication system is essentially one of the forced 
 feed principal. The engine is of the dry sump type. The oil 
 being carried in outside reservoirs. It is therefore necessary 
 to supply two oil pumps, one for delivery of oil through the 
 system, and one for return back to the reservoirs. These two 
 pumps are of the rotary gear type, and are both included in 
 one assembly. The oil goes from the reservoirs to the delivery 
 pump by gravity. From there it goes past a pressure relief 
 valve, (regulated to fifty pounds maximum pressure) to the 
 main oil duct which runs the length of the engine, along the 
 
 55 
 
o 
 
 tf I 
 
 o 
 
 K ij 
 
 w ^ 
 
 L!D ^ 
 
 w 
 
 Ce> .^ 
 
 S -o 
 
 3 ^ 
 
 W S 
 
 H ^ 
 
 56 
 
< -z 
 
 s ^ 
 
 < o 
 
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 y 
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 O *- 
 
 
bottom of the sump. From this duct it goes to the seven main 
 crank shaft bearings, through leads in the webbing. Oil 
 enters the first six crank journals and flows to the crank pins, 
 through holes in the cheeks. Thus lubrication is provided for 
 connecting rod bearings; cylinder walls; etc. The part of 
 this oil not actually consumed, falls back into the sump, with 
 the propellor end of the engine up, it flows direct to the re- 
 turn pump, and thence to the reservoirs. With the propellor 
 end down it collects in a small well near this end of the sump, 
 and goes to the return pump by means of a suction duct, 
 provided for the purpose. Part of the oil is conducted around 
 the main bearing at the propellor end, and goes through out- 
 side leads, to the cam shaft. It flows through these provid- 
 ing lubrication. From here it flows down through the cam 
 shaft drive housings, over the timing gears, to the return pump. 
 
 There is, practically speaking, only one difference between 
 the Liberty engines, as used by the Army and Navy. The 
 former use a higher compression than the latter. This is 
 accomplished by means of a dome topped piston, as against 
 a flat-topped piston. The horse-power developed in the low 
 compression engines, ranges 375-400. While that of the high 
 compression is from 425-450. The weight of both engines is 
 approximately eight hundred and twenty-five pounds (825 Ibs.) 
 and the maximum speed from 1650 to 1800. 
 
 The crank shaft used is a drop forging, having seven 
 bearings and being two and five-eighth inches in diameter. 
 The crank shaft bearings are carried in the webbing between 
 the crank case and the sump; thus making a very rigid con- 
 struction, and giving better constructional alinements. 
 
 The connecting rods are of the "I" beam type twelve 
 inches between centers. They are of the forked type, so that 
 no offsetting of the cylinder banks is required. The left rods 
 are forked, and the right plain. The piston pin is a seamless 
 steel tube, and is a drive fit into the bosses of the aluminum 
 piston. They are of the full floating type, being held in place 
 
 58 
 
^11 
 
 J 
 
 in *o 
 
 ^ 
 
 < o 
 
 ~ * 
 
 5 ^ 
 
 P ^. 
 
 s 
 
 E 
 
 Q 5 
 
 S 'S 
 
 F-*^ ^ 
 
 r-s 
 
 81-1 
 
 Woo 
 
 2 " 
 
 3 S'o 
 ^ u 
 
 W .c a 
 
 M 
 
 ffi o 
 H K 
 
by piston pin retainers. These are small pieces of aluminum, 
 shaped to conform with the piston surface. They are placed 
 in the outer side of each boss, so that while the piston pin 
 is free to move, in both the bosses and the connecting rod, 
 its lateral motion is constrained. By this method of con- 
 struction the danger of the piston pin breaking loose, and 
 scoring the cylinder walls, is done away with. 
 
 The following paragraphs describing the carburetors used 
 in the Liberty engine are reprinted from an article written 
 by the Zenith Carburetor Company. 
 
 "The carburetors used on Liberty engines are of Zenith 
 manufacture and are of duplex, or double, type, and known as 
 their Model US-52. Each barrel is of 52 mm. inside diameter 
 and as two carburetors are used on each 12-cylinder engine 
 there is, in effect, one complete carbureting chamber for each 
 three cylinders." 
 
 "As synchronism is essential, it is necessary that each car- 
 bureting chamber supplies the same amount of a fuel mixture 
 that is itself composed of equal proportions of fuel vapor 
 and air with any given throttle openings. Obviously, all four 
 throttle valves must operate in unison." 
 
 "To accomplish this result it is necessary that each fuel 
 orifice and choke tube shall deliver the same amount of fuel 
 and air under a given suction. The choke tubes, commonly 
 called venturi or chokes, are designed so as to offer the least 
 resistance to passage of the air, and are therefore of a perfect 
 stream line in section. At present, the carburetor setting for 
 the 12-cylinder Liberty engines calls for a No. 31 choke. This 
 means that the throat diameter, or the inside diameter of the 
 choke at its narrowest point, is exactly 31 mm. This is 
 checked by the use of "go" and "no go" ball gauges, and is 
 held accurate within limits of .006"." 
 
 "The main jet sizes now used are, for the high compres- 
 sion Army engines, No. 140, and for the IOW T compression 
 Navy engines, No. 145. The jets are numbered according to 
 
 60 
 
the diameter in 1.100th of a mm. of the fuel orifice, and they 
 are calibrated and carefully gauged for size by means of ac- 
 tual flow of water through them from a height which is kept 
 constant by an automatic level device in the testing tank. The 
 testing is done automatically by an electric and clock device 
 which causes the water passing through the jet to flow into 
 a cubic centimeter graduate for exactly one minute, when the 
 water is diverted, also automatically, into a drain for a period 
 of l /2 minute of time, during which interval another jet is 
 placed in the machine for testing. From experiment and cal- 
 culation it is known that a 1 40-100 mm. jet will flow 335 cu. 
 cm. of water in one minute from a head of 1 meter. The 
 tolerance allowable is 4 cu. cm. over and 1 cu. cm. under. 
 The larger "over" limit is used because the graduate will not 
 always be perfectly drained. The same method of numbering 
 and calibrating is used in the case of the compensating jets. 
 The present setting calls for, in the case of the Army engine, 
 a Xo. 150 Compensator, and, for the Navy engine, a No. 155 
 Compensator." 
 
 A starting and idling device is incorporated in the con- 
 struction of the carburetor which works only when the throttle 
 valves are in nearly closed position. This device consists of 
 the "idling tube" which is drilled at its lower and with a 1 mm. 
 drill for the measuring of the fuel, and at its upper end, 
 with four 1 mm. holes for the measuring of the air; and of 
 a "priming tube" which projects down to about 1 mm. from 
 the bottom of the "idling tube," and which forms a passage 
 for the mixture of fuel and air to the "priming hole" which 
 enters the carbureting chamber at the lower edge of the throttle 
 valves. It should be noted that, as the relative position of the 
 throttle valve and the priming hole determines the suction on 
 the idling device, and consequently the quality of the idling 
 mixture, the throttle valves should all be fitted within very 
 narrow limits and that, when completely closed, the top of 
 the valves should just cover the priming holes. If this point 
 
 61 
 
is noted, it is obvious that the throttle valves will all open 
 in unison and thus be in synchronism. The wide-open posi- 
 tions of the valves will take care of themselves and are, 
 relatively, not so important as the closed positions. As a 
 matter of fact, after the throttle valves are three-quarters of 
 the way open, further opening will not have such influence 
 on. the power or action of the engine. 
 
 When the throttle valves are opened, the suction on the 
 jets overcomes the suction at the priming holes, and the fuel 
 is therefore drawn through the jets and the idling device is 
 automatically put out of action. 
 
 An adjustment is incorporated in the carburetor for the 
 purpose of conserving the fuel supply by taking advantage of 
 the lesser demand for fuel due to the decrease in air density 
 met with in higher altitudes. 
 
 The purpose is accomplished by "putting a brake" on the 
 fuel supply thru the jets. The carburetor fuel bowl normally 
 has atmospheric pressure existing within it, and this pressure 
 is reduced by placing it in communication, thru a suitable 
 channel and adjustable valve, with the inside of the carburetor 
 barrel, where a low pressure condition exists during the run- 
 ning of the engine. By thus reducing the pressure on the 
 jets, their flow is decreased to a point where it compensates 
 for the lesser weight of air being drawn into the carburetor, 
 a proper air-gas mixture ratio is maintained, and wastage 
 fuel eliminated. 
 
 LIBERTY-DELCO IGNITION SYSTEM 
 
 The ignition system as used on the Liberty engine is of 
 Delco design, and made by the Dayton Engineering Labor- 
 atories of Dayton, Ohio. It is a battery generator system and 
 primarilly operates on the principle of the battery system, as 
 described previously. 
 
 The system consists essentially of six units, viz: two 
 
 62 
 
THE LIBERTY ENGINE MODEL B 
 
 Showing the incorporation of a reduction gearing enabling higher 
 engine speeds and consequently increased Horse Power Output. 
 The gearing keeps the propeller speed down to an efficient range. 
 
 63 
 
distributor heads, storage battery, generator, switch, and volt- 
 age regulator. Both distributor heads are identical and con- 
 tain the breaker mechanism, condensor, induction coil, and 
 distributor. The distributor segments, coils and secondary 
 terminals, are encased in Baekelite so that they are fool proof. 
 Also the coils are protected from dampness and consequent 
 deterioration. This Baekelite assembly fastens to the rest of 
 the head by clamps and thumb screws which act as coil ter- 
 minals. Also contained in the entire assembly are the breaker 
 mechanism, condenser, and distributor arm. 
 
 The battery supplies the current for starting and is a 
 four cell three volt storage type. The generator is a four 
 pole, shunt wound, direct current machine, so arranged that 
 at engine speeds of 650 r.p.m. and over it generates sufficient 
 current to supply ignition and charge the battery. The volt- 
 age regulator is used so that the charging rate may be kept 
 constant and not increase excessively due to the increase of 
 engine speeds. It operates on the Tyrrel principle by fluctuat- 
 ing the generator field strength rapidly and consequently keep- 
 ing the voltage output at what may be taken as a constant 
 value. The switch assembly is a combination of two switches ; 
 one to control the left hand distributor head, which is placed 
 on the timing gear end of the left hand cam shaft; the other 
 to control the right hand head located correspondingly on the 
 right hand cam shaft. The switch is so arranged as to con- 
 trol the circuits to each of the distributors, and generator 
 to battery circuit. It also includes an ammeter which has 
 proven very useful since it tells the condition of the ignition 
 system at all times. 
 
 The ammeter shows the charging rate of the generator, 
 or the discharging rate of the battery whenever either or both 
 switches are on, and at all engine speeds. Each distributor 
 is connected to give twelve sparks every two revolutions of 
 the crank shaft, thus firing one spark plug in each of the 
 twelve cylinders. The advantage of this is more positive and 
 
 64 
 
complete ignition, providing both sparks occur at the same 
 instant, as they must be timed to do. This also provides a 
 larger safety factor, since the engine will run with only one 
 spark plug in each cylinder firing, the only effect being a slight 
 drop in r.p.m. 
 
 The breaker mechanism, instead of having only one set of 
 breaker points, has two sets, w r hich are arranged in parallel 
 and termed accordingly the parallel breakers. The advantage 
 is again safety factor and the additional path for current 
 flow when the points are together for an extremely short in- 
 terval, as is the case at high engine speeds. Naturally two 
 breaker points offer less resistance to the current flow than 
 would one. The use of the safety factor is apparent in that 
 one set of points may stick open, or become entirely inoper- 
 ative for some reason, and yet the other set will carry the 
 load and the engine will operate without hindrance ; the only 
 difference being a slightly less intense spark at high speed. 
 
 In a battery ignition system the source of current, being 
 always constant, will cause induction to take place whenever 
 the primary circuit is broken, regardless of the direction of 
 rotation, as it is very often necessary, particularly when crank- 
 ing by the propeller, to rock the motor. It may be readily 
 seen that sane means be used to prevent ignition occurring, 
 so that the danger of a back kick may be eliminated. This 
 is accomplished by means of an auxiliary or third breaker 
 point. This is also incorporated in the distributor, and is con- 
 nected in parallel with the parallel breakers. It is so placed 
 and timed, so that when the engine is rotated in the proper 
 direction it will open slightly before the main points, thus 
 causing no hindrance to the proper break. A small resistance 
 unit is connected in series with the third breaker. 
 
 \Yhen rotation in the improper direction occurs, the main 
 points open first and the third point remaining closed, pro- 
 vides a connection to the ground. Due to the resistance unit 
 the primary current is so weakened in value that \vhen the 
 
 65 
 
third point does open the induction caused is not strong enough 
 to produce a spark. It must be noted, however, that this does 
 not prevent the occurrence of one spark due to cranking with 
 the spark in the advanced position. Consequently it is possible, 
 as in any engine, to obtain a back kick, if the spark is not 
 retarded when starting. It is, however, impossible for counter 
 rotation to occur to more than this extent. 
 
 The cam that operates the breakers has twelve lobes, and 
 rotates at cam shaft speed. These lobes are spaced 22.5 and 
 37.5 apart. This unequal spacing is brought about by the 
 angle between cylinder banks (45) which causes unequally 
 spaced power impulses, consequently, unequally spaced sparks 
 must be delivered. The battery is a storage type having four 
 cells, its voltage when fully charged is approximately nine 
 volts and must never be allowed to become discharged. The 
 battery is tested with a hydrometer syringe, and the specific 
 gravity of the electrolyte should be 1.280 to 1.310 for a full 
 charge. To test battery with hydrometer, lay battery on side 
 until electrolyte has run into the top chamber, then suck it out 
 with hydrometer. The battery is of the non-spillable type, 
 and differs from the ordinary automobile battery only in that 
 respect. As the generator is only intended to keep the bat- 
 tery fully charged, and not to recharge a discharged battery, 
 a battery that shows a hydrometer reading of 1.225 or less 
 should be taken off and charged from an external source. 
 
 The generator requires no attention except for an oc- 
 casional oiling. 
 
 The regulator has one adjustment, and should not be in- 
 terferred with. The charging rate of the generator is 1.5 
 to 3 amperes, and should only be adjusted with a fully charged 
 battery, and by someone familiar with the regulator. 
 
 The switch contains the ignition resistance units which 
 are connected in series with the distributors. The function 
 of these resistance units is to control the flow of current when 
 the engine is being started or is running slow. If the engine 
 
 66 
 
is stopped and one switch is thrown on (either one), the 
 battery, is connected to the distributor controlled by that switch. 
 If the breaker contacts have closed, there would be a very 
 heavy discharge of current, which would soon weaken the 
 battery. To overcome this the resistance unit is used, and it 
 will only allow a discharge of 4 to 5 amperes (registered on 
 amperes meter), which is all the current necessary for ignition. 
 
 The engine is always started with one switch (either one) 
 "on" and both switches should not be thrown "on" until the 
 engine is running 650 r.p.m. or faster. With one switch 
 on the battery is supplying the current, and the ampere meter 
 will show a discharge; with both switches on and an engine- 
 speed of 650 r.p.m. or faster, the generator is supplying the 
 current, and the ampere meter will show "charge." It can be 
 seen from the above, that with both switches on and an 
 engine-speed of less than 650 r.p.m., the battery would be 
 supplying the current for both distributors, and that the battery 
 would also be discharging through the generator. The result 
 would be a heavy drain on the battery, which would soon 
 result in its being damaged, or completely exhausted. Con- 
 ditions such as this are always indicated by a heavy "dis- 
 charge" on the ampere meter and should be avoided by throw- 
 ing "off" one switch. 
 
 In order that the operation of the switch may be made 
 clear, a diagram showing three positions of the switch is 
 shown on the preceding page. 
 
 Figure 1 shows the right switch in the position "on" 
 for starting. The right switch moves the two blades G, and 
 H, on and off the three contacts. These two blades are con- 
 nected together. It can be seen that current will flow from 
 the battery connected at A, through the ampere meter, then 
 through the two blades, and out through the resistance unit 
 (crooked line) to the right distributor connected at D. 
 
 67 
 
68 
 
Figure 2 shows the left switch in the position "on" for 
 starting, and the same conditions prevail as in figure 1. ex- 
 cept that the two blades E, and F, are insulated from each 
 other, so that current flows through each blade independent 
 of the other. It will be noticed in figures 1 and 2 that the 
 ampere meter shows a discharge of approximately 4.5 amperes. 
 The meter should always have a discharge of approximately 
 4.5 amperes, with engines stopped and one switch "on" pro- 
 vided the breaker points in the distributor are closed. 
 
 Figure 3 shows both switches "on/' and the meter indi- 
 cating "charge." This condition is indicated for engine speeds 
 of over 650 r.p.m. as the generator is now supplying the 
 current. The generator circuit is completed from C through 
 the blade F to blade H, from this blade the current can be 
 traced to both distributors and to the batterv. 
 
 69 
 
70 
 
71 
 
ORDER OF TEARDOWN 
 
 U. S. N. LIBERTY MOTOR SCHOOL 
 
 1. Distributor head and high tension wire conduit. 
 
 2. Drain all oil. 
 
 3. Distributor mechanism. 
 
 4. Oil pipes. 
 
 5. Camshaft assembly. 
 
 6. Generator. 
 
 7. Mark carburetor and intake headers. 
 
 8. Water pipes and hose. 
 
 9. Breathers. 
 
 10. Carburetors. 
 
 11. Intake headers. 
 
 12. Propeller hub. 
 
 13. Cylinders. 
 
 14. Oil pump assembly and pump cover. 
 
 15. Water pump assembly. 
 
 16. Two camshaft drive shaft gear assembly. 
 
 17. Oil pump driving gears. 
 
 18. Water pump driving gears and shaft assembly. 
 
 19. Piston pin retainers. 
 
 20. Pistons. 
 
 21. Upper half crankcase. 
 
 22. Crank assembly. 
 
 23. Connecting rods and thrust bearing. 
 
 NOTE: Each part to be thoroughly oiled to resist rust, and 
 each part (where there is opportunity of mixing up) to be 
 tagged. 
 
 72 
 
TEARDOWN 
 
 U. S. X. LIBERTY MOTOR SCHOOL 
 
 1 DUAL IGNITION SYSTEM: 
 
 (a) Each distributor fires one plug in each cylinder through- 
 out entire cylinders. 
 
 (fr) Right distributor fires plugs on gear side of cylinder 
 while the left fires the propeller side. 
 
 (c) Disconnect high tension conduit which is attached to 
 outlet water header by cap screws with no washers. 
 
 (d) Remove the twelve insulated wires fastened to spark 
 plugs, being careful not to spring ball-clips. Rubber 
 ferrules on end, must be in perfect condition to assure 
 perfect insulation. 
 
 (c) Remove distributor heads held by wire clips along with 
 the conduit. Care should be taken to bind the brushes 
 with a rag or rubber band to prevent any breakage. 
 
 2 CAMSHAFT HOUSING ASSEMBLIES : 
 
 (a) Remove distributor tie rod found in upper holes with 
 
 boss down. 
 (6) With spanner wrench remove collars on camshaft 
 
 housings. A felt washer should be inserted in each 
 
 collar to prevent oil leakage. 
 
 (c) Loosen castle nuts on the twelve studs of each cam- 
 shaft housing. Plain washers arc found under each 
 nut. 
 
 (d) Disconnect oil pipes leading to camshaft before re- 
 moving camshaft assemblies which are marked either 
 right or left. 
 
 (f) Male splines on jack-shaft marked by a groove in one 
 
 tooth. 
 (f) Female spline carried two niches on collar. Both splines 
 
 must coincide for timing. 
 
 73 
 
3 GENERATOR: 
 
 (a) Held by three castle nuts on studs. Plainwashers. Oil 
 paper gaskets are found between generator pad and scat. 
 (fr) Only one bearing in generator. 
 
 (c) Power connections not marked. 
 
 (d) Splines must fit closely to prevent any back lash (conic 
 out rather hard). 
 
 4 CARBURETORS : 
 
 (a) Unfasten carburetor tie-rod. Purpose of rod to make 
 carburetors work simultaneously. 
 
 (b) Watch taper pins that lock tie-rod. 
 
 (c) Be careful of pins. Easily lost. 
 
 (d) Two copper asbestos washers separate each carburetor 
 from manifold. 
 
 (c) Although interchangeable, mark each carburetor pro- 
 peller end and gear end. 
 
 (/) Each carburetor held by two anchor bolts with plain 
 washer fastened to hot water intake header. 
 
 5 HOT WATER INTAKE HEADER: 
 
 (a) Held by four castle Huts with washers at each end, 
 having also two oil paper gaskets. 
 
 (b) This parts, with carburetor, removed practically at the 
 same time, holding one in each hand. 
 
 6 MANIFOLD OR INTAKE HEADERS: 
 
 (a) Four in number, each held by six studs, castle nuts and 
 washers, paper gaskets between each. 
 
 (b) Each manifold stamped on exhaust port flange pro- 
 peller end R. or L. and gear end R. or L. as the case 
 may be. 
 
 (c) Remove that manifold with with smallest bearing sur- 
 face first. Found hire to be right side. 
 
 (d) Inspect manifolds for loose cores which rattle. 
 
 74 
 
7 WATER SYSTEM: 
 
 (a) Remove both outlet water pipes from pump. Right 
 side is longer than left. 
 
 (b) Remove inlet water headers; both pipes are inter- 
 changeable (hose hands). 
 
 (c) Remove outlet water pipes of cylinders. Loosen all 
 hose bands attached to cylinder. 
 
 (d) Three flanges attached to each manifold and held there 
 by two cap screws through each flange having driller 
 heads (paper gaskets between manifolds and each 
 flange). 
 
 (e) Centrifugal water pump held by four studs with castle 
 nuts. Paper gaskets separate pump pad and seat. 
 
 (/) Pump intake points to the left, plugged hole found at 
 the bottom. 
 
 8 BREATHERS (CRANKCASE) : 
 
 (a) Held by two studs washers and castle nuts, has paper 
 gasket between, also baffle plate screen. 
 
 (b) On propeller end the three way distributor for oil fast- 
 ened by two castle nuts, washers and has an oil paper 
 gasket. 
 
 9 CYLINDERS (12): 
 
 (a) Start from gear or propeller end and remove flange 
 
 nuts between each cylinder. Six other castle nuts serve 
 
 to hold skirt flange to cylinder pad. 
 (fr) Paper gaskets between cylinder pads and flanges are 
 
 cut to cover three cylinders. 
 
 (c) Remove one spark plug before pulling cylinder off pis- 
 ton to relieve vacuum. 
 
 10 PISTONS: 
 
 (a) Bind studs at base of cylinder pad to prevent scratch- 
 ing of pistons. 
 
 75 
 
(b) With pliers remove piston pin retainers. 
 
 (c) Drive out piston with brass plug, pounding it gently. 
 
 (d) Piston pin should only he driven far enough to clear 
 pin housing. 
 
 (e) Each piston is marked right or left and its numerical 
 position. 
 
 (/) Allow rings in grooves to remain untouched. 
 
 (g) Rings are common split type with two right and one 
 
 left. The splits being set at 180 degrees apart. 
 (/*) While removing piston pin, hold piston firmly so as not 
 
 to throw connecting rods out of line. 
 
 11 GENERATOR AND CAMSHAFT ASSEMBLIES: 
 
 (a) Remove gear case cap held by six cap screws drilled 
 for wiring, no washers. 
 
 (b) Remove jackt shaft assemblies held by four studs and 
 castle nuts. 
 
 (f) Should have a paper gasket between crank case and 
 pad. 
 
 (d) Each shaft marked right or left on the beveled gear, 
 (r) Ball race retainers in assembly. 
 
 (/) These shafts must be removed before generator shaft, 
 as gears of former prevent removal of latter. 
 
 REMOVE GENERATOR DRIVE SHAFT: 
 
 (a ) Duty: to drive generator and two jack shafts. 
 
 (b) Construction: With key-way in shaft for jack shaft 
 gear and two spacing sleeves to hold it where it belongs. 
 
 (c) Bevel gear has twenty-two teeth. 
 
 12 TIMING: 
 
 (a) When No. 1 and No. 6 are 10 degrees past dead center, 
 splines should be placed in line with center of cylinder. 
 
 76 
 
13 REMOVAL OF LOWER CRAXKCASE: 
 
 (a) Loosen fourteen nuts on anchor bolts, a plain washer 
 is found beneath each. 
 
 (b) Turn crankcase over allowing an anchor flange to 
 rest on wooden blocks mounted on frame. 
 
 (c) Remove two through bolts on each end of base. Also 
 two anchor bolts nuts were found at propeller end and 
 removed. Remove oil pump held by ten castle nuts 
 with washers. A paper gasket found between. 
 
 (J) Remove fifty hexagon head holding upper and lower 
 crankcases together. 
 
 (e) Lift off lower part of crankcase. 
 
 14 REMOVAL OF SPOOL GEAR: 
 
 (a) Loosen set screw which holds assembly in place. 
 
 (b) With case upright drive assembly through. 
 
 (c) Upon measuring it it is found to be tapered .0007" over 
 a distance of 2y 2 ". 
 
 15 FORK AXD PLAIX EXD COXXECTIXG RODS: 
 
 (a) End play of connecting rod allowed .006", found to be 
 as great as .016". 
 
 (6) Babbitt metal bearing surface on fork rods- 
 bronze on plain end. 
 
 REASOX : 
 
 (f ) Plain end rod is removed first by turning shaft to allow 
 it to let go easily upon removing nuts. 
 
 (</) Forked rods followed, care being taken to place both 
 halves of bearing surface as they originally were. 
 
 16 UPPER HALF CRANKCASE: 
 
 (a) Ispect bearing surfaces high spots shows up bright 
 
 (should be a lead color throughout). 
 (6) Watch studs for loosening up. 
 (c) Care should be taken to find any cracks or sand holes. 
 
 77 
 
CRANKSHAFT INSPECTION: 
 
 (a) Inspect crank pins and main bearings for any scratches 
 or rough spots. 
 (Crocus cloth will remove any slight scratches.) 
 
 (&) Teeth of driving gear on gear flanges should be per- 
 fect and not chewed up. 
 
 (Pricked punched 12 degrees 30' past center for timing 
 purposes). 
 
 17 CAMSHAFT ASSEMBLY: 
 
 (a) Remove the six plates holding rocker arms in place, 
 held by 3 hexagonous bolts and plain washers. 
 
 (b) Withdraw bearing retainers which are set screws used 
 to hold bearings in place. 
 
 (c) Remove oil cap on gear end with a spanner wrench. 
 
 (d) Remove 6 hexagonous nuts which hold distributor 
 flange in place. 
 
 (c) Withdraw camshaft with bearings attached. 
 
 (/) Split bearing surface held by set screws bearings are 
 
 aluminum throughout except at gear end, which is a 
 
 bronze bearing. 
 
 78 
 
HISPANO SUIZA 
 
 MODEL "A" 
 
 8 Cylinders Ycc type. Angle between cylinder banks 90. 
 
 Bore 4.72 inches. Stroke 5.11 inches. 
 
 Horse-power 150 at 1,450 r.p.m. 
 
 Cooling Water circulated by a centrifugal pump. 
 
 Lubrication Force feed. 
 
 Carburetion Zenith Duplex Model 48 D. C. 
 
 r , fl Exciter magneto. 
 
 hnntwn {_ , , , . ,_. 
 
 12 Dixie magnetos Model 800. 
 
 Intake opens 10 PTC. 
 
 IT* T :^: nfl Intake closes 50 PBC. 
 
 Valve liming _ .^^ 
 
 Exhaust opens 4^ BBC. 
 
 Exhaust closes 10 PTC. 
 Spark occurs 20 20' BTC. 
 Conditions for best results Water at outlet 165 to 175 Fahr. 
 
 Oil temperature 130 Fahr. 
 Firing order 1L-4R-2L-3R-4L-1R-3L-2R. 
 Oil pressure When fitted with a relief valve can be varied and 
 
 is usually about 60 Ibs. per square inch. 
 Valve clearance .0787" '. 
 Breaker gap .020". 
 Spark plug gap .020". 
 
 Two of the oustanding features of this engine are the cyl- 
 inder construction, and cam action. 
 
 There are two blocks of four cylinders each, here again 
 the steel sleeve is used. These sleeves are threaded on the out- 
 side, and four of them screwed into an aluminum casting which 
 forms the water jacket. This gives a very light assembly and 
 one which lends itself particularly well to stream lining. 
 
 The cam shafts are driven in practically the same way as 
 on the Liberty, but no rocker arms are used. The valve stems 
 are fitted with circular steel pieces which screw into them, 
 
 79 
 
THE HISPANO SUIZA ENGINE 
 MODEL XE 300 H. P. 
 
 Showing the stream line effect obtained by the en bloc construction 
 of the water jackets and the method used in housing the cam shafts. 
 The constructional features of this model are very similar to all 
 other models of the same engine. 
 
 80 
 
against the action of the valve spring. These are called mush- 
 rooms, and the valve clearance is adjusted by screwing these 
 in or out. The cam shaft is held on the top of the cylinder 
 blocks, by three bronze bearings. The cams themselves act 
 direct on the mushrooms, so that there is absolutely no lost 
 motion. There is an almunium cover which encloses the cam 
 shafts, and again very good stream lining is accomplished. 
 
 Each block of cylinders, after assembly, are given several 
 coats of enamel, both inside and out, each coat being thoroughly 
 baked on. The lower end of each cylinder projects, and has a 
 flange, by means of which the blocks are fastened to the crank 
 case. 
 
 The pistons are ribbed aluminum castings, provided with 
 four rings each, in two grooves at the top. The piston pins are 
 hollow, and are made of alloy steel case hardened. They are 
 held in the piston bosses by means of a single long set screw, 
 which passes entirely through them. 
 
 The crank shaft is of the regular four-cylinder type, that 
 is, having four throws, 180 between throws. It is of chrome 
 nickel steel and provided with four bearings of the regulation 
 bronze backed, babbit lined type. In addition to this there is 
 an annular ball bearing at the cranking end. A double row ball 
 thrust bearing is located at the propeller end. The crank shaft 
 is bored hollow for lightness and for oiling. 
 
 The connecting rods are made of heat treated alloy steel, 
 and are tubular in section, they are of the forked type, as in 
 the Liberty, and carry a bronze bushing in the upper end. The 
 crank shaft bearings are carried in the webbing of the crank 
 case and sump, as in the Liberty. The sump is fastened to 
 the crank case by bolts running through the webbing and 
 also by a series of bolts around the outer edges. All joints are 
 lapped, that is; no gaskets are required. 
 
 Lubrication is of the force feed type. Pressure is provided 
 by a sliding vein eccentric pump. Oil is carried in the sump. 
 The pump is mounted in the sump, directly below the crank 
 
 81 
 
shaft gear. From the pump the oil goes through a removable 
 screen filter, to the main oil duct, from this, to three of the 
 main bearings, thence through the hollow crank shaft, to the 
 four crank pins, lubricating the connecting rod bearings, and 
 by spray, the piston pins, cylinder walls, etc. Oil is led up to, 
 and around the fourth main bearing, from there it goes through 
 outside leads, to the hollow cam shafts. It passes through these, 
 lubrication being provided by a small hole in each cam surface. 
 From the cam shafts it returns to the sump, passing through 
 the cam shaft drive housings, and over the timing gears. It 
 also lubricates, on its return, the crank shaft ball bearings. 
 
 Ignition is provided by two 8-cylinder type Dixie magnetos, 
 firing one spark plug in each cylinder. One magneto is driven 
 from each of the two vertical shafts. Small bevel pinions mesh 
 with bevel gears on each magneto shaft. No packing is neces- 
 sary to prevent loss of oil at these points. The oil is prevented 
 from escaping by grooves out in the housings. The magnetos 
 are of the set spark type, ignition occurring at 20 20' before 
 T. D. C. For this reason it is necessary to provide a distributor 
 which has two brushes, one for running ignition, the other for 
 starting. When starting ignition is provided by a separate hand 
 exciter, this gives a shower of sparks to the second on starting 
 brush. This, in effect, is the same as a greatly retarded spark. 
 Before starting it is well to turn the engine over a few times, 
 with all ignition off, in order that a good charge may be taken 
 into each cylinder. 
 
 For use on sea planes, a geared down hand crank is pro- 
 vided. In this event the exciter is geared to the starting crank. 
 
 Carburetion is provided by a double jet Zenith carburetor 
 model No. 48 D. C. It is very similar in construction and op- 
 eration to the Model U. S. 52, used in the Liberty. The intake 
 manifold is water jacketed and runs crosswise between the cyl- 
 inder blocks. 
 
 Cooling is provided by means of water circulated by a 
 centrifugal pump, which is located at the cranking end of the 
 engine, under the sump. 
 
CURTISS 
 MODEL OXX6 
 
 8 Cylinders Vee type. Angle between cylinder banks 90. 
 
 Bore 4.25 inches. Stroke 5 inches. 
 
 Horse-power 100, at 1,400 r.p.m. 
 
 Cooling Water circulated by a centrifugal pump. 
 
 Lubrication Force feed. 
 
 Ignition Two Dixie magnetos. 
 
 Carburetion Zenith Duplex. 
 
 Intake opens 1/16" PTC. 
 
 Valve Timing . 
 
 Intake closes 1/2" PBC. 
 
 Exhaust opens 13/16" BBC. 
 Exhaust closes 1/32" PTC. 
 Ignition occurs Full advanced BTC. 
 Firing or derl -2-3-4-7-8-5-6-. 
 Valve clearance .010". 
 Breaker gap .020". 
 Spark plug gap.Q2Q". 
 
 The Curtiss O X and O X X engines are probably the most 
 widely known and used of any in the American field. The O X 
 is the army type and is of four inch bore and five inch stroke, 
 while the O X X or Navy type differs only in that its bore is 
 four and one-quarter inches. 
 
 The cylinders are steel sleeves surrounded by water jackets 
 of Monel metal. They are constructed separately and fasten 
 to the crank case by means of a flange, secured by studs, and 
 also by four long studs which extend the height of the cylinder 
 and fasten to a bracket at the top. 
 
 The engine is provided with one cam shaft, located in the 
 crank case. The valves are located in the heads of the cylin- 
 ders, the cam action being conveyed by the rocker arms, and 
 push rod method. As applied to this model engine, the particu- 
 lar valve action may be called characteristic. The exhaust valve 
 is operated in the regular manner as applied to an action of 
 
 83 
 
THE CURTISS MODEL OXX ENGINE 
 
 Showing the Push and Pull Rod type of valve operating mech- 
 anism and general assembly. Note the location of the carburetor 
 which facilitates gravity feed. 
 
 84 
 
this type. In other words, when the high point or toe of the 
 cam is up, the push rod rises and the rocker arm forces the valve 
 off the seat. It is the operation of the intake valve which dif- 
 fers from conventional practice. It may be said to be operated 
 by the pull method. The intake cam is split, being on either 
 side of the exhaust cam, the intake cam follower is held on the 
 cam surface constantly by spring action. There is a hollow rod 
 surrounding the exhaust push rod. The lower end of this rod 
 rides on the intake cam follower while the upper end is at- 
 tached to the intake rocker arm. By spring action, which is 
 very strong, the intake valve is forced off the seat when the 
 cam follower is on the low point or heel of the intake cam. 
 When it is on the toe of the cam, the rocker arm 'is held up, 
 away from the valve stem, and the valve is closed. The greatest 
 advantage of this valve action is economy of space. 
 
 The pistons are aluminum castings, and the hollow steel 
 piston pins are secured by a set screw in one piston boss. 
 
 The crank shaft has four throws 180 apart, and is sup- 
 ported by five main bearings of the bronze backed babbit lined 
 type. Half of each bearing is carried in the webbing of the 
 crank case while the other half is carried in a bearing cap 
 which is bolted to the crank case webbing, thus securing the 
 crank shaft. This construction makes possible the dropping of 
 the sump, without interfering with the support of the crank 
 shaft. 
 
 The connecting rods are heated treated drop forgings of 
 the I section type. They fasten side by side on each crank pin. 
 It is therefore necessary to set one bank of cylinders ahead of 
 the other. 
 
 The lubrication system is of the forced feed type. The 
 sump is the reservoir and carries a sight gauge, and is so con- 
 structed that its center is always the lowest point. Two baffle 
 plates are provided, which slope from the ends of the sump 
 towards the center, and leave a three-quarter inch opening at 
 that point. This opening extends the width of the sump. A 
 
 85 
 
rotary gear pump is located in the low point of the sump. Oil 
 from this goes to the hollow cam shaft, lubricating its bearings, 
 thence through leads to the crank shaft bearings, through the 
 hollow crank shaft, to the crank pins, lubricating the connecting 
 rod bearings, and by spray the piston pins, cylinder walls, etc. 
 The timing gears and thrust bearing are lubricated by spray. 
 A pressure relief valve is located in the line. On returning, 
 oil flows over the baffle plates and into the sump. 
 
 Ignition is provided by two 8-cylinder Dixie magnetos, 
 located at each end of the crank case, between cylinder banks. 
 Each magneto fires are spark plugs in each cylinder. They 
 are provided with an advance-retard lever. 
 
 Carburetion is provided by a Zenith double jet carburetor, 
 operating on the regular Zenith principle. It is located at the 
 timing gear end of the engine, below the sump. The gases are 
 conducted to the cylinders by means of long manifolds which 
 are water jacketed at the lower ends. 
 
 The cooling system is of the ordinary type, water being 
 circulated by a centrifugal pump which is located at the timing- 
 gear end of the engine, on a level with the crank shaft. 
 
 MATERIALS OF CONSTRUCTION 
 
 The following is given, as an outline, setting forth briefly, 
 the general types of material used in the construction of the 
 present day aviation engine. 
 
 Cylinder: Cast iron is sometimes used where economy of 
 weight is not so essential. When it is used the water jackets 
 are ordinarily cast integral with the cylinders. 
 
 Where economy of weight is important, a sleeve of heat 
 treated alloy steel is used. With this type of construction the 
 water jacket is made of pressed steel, and welded on, as in the 
 Liberty, or the sleeve is fitted in an aluminum block, as in the 
 Hispano Suiza. 
 
 Piston: Aluminum, cast iron and semi-steel are used. The 
 
 86 
 
first is the most common, not only on account of lightness, but 
 because of its better heat conductivity. 
 
 Piston pin: Drop forging of alloy steel, hollowed out, heat 
 treated, and case hardened. 
 
 Connecting rod: Drop forging of alloy steel, often of 
 chrome nickel composition, usually of "I" beam action and ma- 
 chined all over. 
 
 Piston Rings: Cast iron, used because it is softer than steel, 
 and will not scratch the cylinder walls. 
 
 Valves: Drop forgings, usually of Tungsten steel, and heat 
 treated. The presence of Tungsten gives steel the power to 
 withstand enormous strains, even up to cherry red heat 
 
 Crank Shaft: Drop forging of chrome nickel steel, heat 
 treated and machined all over. The presence of chromium en- 
 ables steel to withstand the succession of hammer like blows, 
 while nickel increases the tensil strength. 
 
 Cam Shaft: Drop forging of heat treated alloy steel, with 
 cams forged on the shaft and their surface case hardened. 
 
 Crank case and Sump: Aluminum castings, ribbed for 
 strength, and to provide bearing surfaces. 
 
 Bearings: Usually bronze backed, Babbit lined. Babbit is 
 a metal composed of antimony, lead and tin, and has a low 
 melting point. Used at friction points, so that if heat becomes 
 excessive, the Babbit will melt and prevent injury through 
 seizure. 
 
 Bushings: Usually bronze. Used at points of wear, so that 
 they may be easily taken out and replaced, without the neces- 
 sity of providing large and expensive parts= 
 
 87 
 

 
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INDEX 
 
 Page 
 
 Advanced Spark 47 
 
 Reasons for 4< 
 
 Effects of 4 i 
 
 Advanced Timing 4^ 
 
 After Firing 15 
 
 Causes of 34 
 
 Air Bled Jet 32 
 
 Air Cooling 22 
 
 Air Gap 3! 
 
 Altitude Adjustment 30 
 
 Reasons for 31 
 
 Effects of 31 
 
 Aluminum Pistons 86 
 
 Angle Between Banks 21, 53 
 
 Ammeter 64 
 
 Ampere 35 
 
 Armature 41 
 
 Auxiliary Air Valve 2 
 
 Babbit 87 
 
 Back-fire, Definition of 15 
 
 Causes of 34 
 
 Back Kick 15 
 
 Bakelite 64 
 
 Battery Ignition 36, 62 
 
 Bearing 11 
 
 Construction of 87 
 
 Berling Magneto 41 
 
 Bore 14 
 
 Bosch Magneto 41 
 
 Breaker Cam 38 
 
 Breaker Mechanism 37 
 
 Breaker Points 38 
 
 Adjustment 39 
 
 Bushing 11 
 
 Construction of 87 
 
 Cam Shaft . ..11-14 
 
 Cap Jet 29 
 
 Carburetion 2fi 
 
 Carburetor, Curtiss 86 
 
 Hispano-Suiza 82 
 
 Liberty 60 
 
 Master 32 
 
 Miller 32 
 
 Model 48 D. C 82 
 
 Model U. S. 52 60 
 
 Simple 26 
 
 Stromberg 32 
 
 Zenith 26,60 
 
 Centrifugal Pump 23 
 
 Circuit . . . 37 
 
 Page 
 
 Coil, Induction 37 
 
 Primary 37 
 
 Secondary 37 
 
 Combustion Chamber 3h 
 
 Compensator 27 
 
 Compound Xozzle 27 
 
 Compression 16 
 
 Condenser 38 
 
 Failure of 31) 
 
 Conductor 35 
 
 Connecting Rod 10, 14 
 
 Construction of 87 
 
 Construction, Materials of 8<> 
 
 Contact 15 
 
 Cooling 22 
 
 Cooling System ~'-> 
 
 Temperature of 23 
 
 Crank Case, Definition of 14 
 
 Construction of 87 
 
 Crank Shaft 11-14 
 
 Construction of 87 
 
 Rotation, Degrees of 45 
 
 Curtiss Engine 83 
 
 Cam Shaft S3 
 
 Carburetion 86 
 
 Connecting Rod 85 
 
 Cooling 86 
 
 Crank Shaft 85 
 
 Cylinder 83 
 
 Ignition 86 
 
 Lubrication 85 
 
 Pistons 85 
 
 Specifications of 83 
 
 Valve Operation 83 
 
 Cycle 14 
 
 Beginning of 16 
 
 Four Stroke 15 
 
 Principle and Operation of 15 
 
 Cylinder, Purpose of 10-11 
 
 Construction of 86 
 
 Dead Center 14 
 
 Delco Ignition 62 
 
 Ammeter 64 
 
 Battery 64 
 
 Breaker Mechanism 65 
 
 Breaker Points 65 
 
 Cam 66 
 
 For Running 67 
 
 For starting 67 
 
 Generator 64 
 
 Regulator 64 
 
 Resistance 66 
 
 Switch 67 
 
 93 
 
INDEX Continued 
 
 Page 
 Dielectric ....................... 38 
 
 Direction of Rotation, Determina- 
 tion of ....................... 46 
 
 Distributer ..................... 40 
 
 Segments ..................... 40 
 
 Arm ......................... 40 
 
 Dixie Magneto .................. 42 
 
 Diagram of ................... 43 
 
 Sparks per Revolution ......... 42 
 
 Speed of Rotation .............. 42 
 
 Dry Sump ...................... 24 
 
 Advantages of ............... 24-25 
 
 Reasons for .................. 24 
 
 Duct, Main ..................... 24 
 
 Oil .......................... 24 
 
 Eight Cylinder Arrangement ...... 21 
 
 Electricity ...................... 35 
 
 Electro-Magnet ................. 35 
 
 Electrode ....................... 36 
 
 Emergency Repairs .............. 49 
 
 Engine Characteristics, Liberty... 51 
 
 Curtiss ....................... 83 
 
 Hispano-Suiza ................ 79 
 
 Exhaust Flame, Color of ......... 34 
 
 Exhaust Stroke 
 
 Failure of Condenser 
 
 Firing Order, Determination of . . . 
 
 Curtiss 
 
 Hispano-Suiza 
 
 Liberty 
 
 Flame, Exhaust 
 
 Float Chamber . 
 
 Flux ; ; ; ; ; 
 
 Reversal of 38 
 
 Force Feed Oiling 
 
 Force Lines of 
 
 Four Stroke Cycle 
 
 Frequency 
 
 Full Force Feed 
 
 Geared Propeller Drive 
 
 Generator Delco 
 
 Ground 
 
 High Frequency 
 
 Hispano-Suiza Engine . , 
 
 Cam Shaft 
 
 Carburetor 
 
 Connecting Rods 
 
 Cooling 
 
 Crank Shaft 
 
 Cylinder Construction 
 
 Ignition 
 
 Lubrication . 
 
 16 
 
 39 
 48 
 83 
 79 
 51 
 34 
 26 
 35 
 42 
 25 
 35 
 15 
 39 
 25 
 
 19 
 64 
 
 40 
 
 39 
 79 
 79 
 82 
 81 
 82 
 81 
 81 
 82 
 81 
 
 Pistons 
 
 Specifications of 
 
 Starter 
 
 Valves . . . 
 
 Page 
 . . 81 
 . . 7!) 
 . . 82 
 . . 71) 
 
 "I"-Head 17 
 
 Idling if, 
 
 Idling Device 27, 33 
 
 Ignition 9, 16, 36 
 
 Delco 62 
 
 Magneto 41 
 
 Impeller 23 
 
 Improper Carburetion 33 
 
 Induction, Definition of 35 
 
 How Accomplished 35-36 
 
 Insulator 35 
 
 Intake Stroke 16 
 
 Jet . 
 
 26 
 
 "L"-Head 17 
 
 Lean Mixture, Effects of 34 
 
 Liberty Engine 51 
 
 Angle Between Banks 53 
 
 Army Type 58 
 
 Battery 64-66 
 
 Cam Shaft 55-57 
 
 Carburetor 60 
 
 Compression 58 
 
 Connecting Rods 58-59-60 
 
 Cooling 55 
 
 Crank Shaft 58 
 
 Cylinder 53-54-55 
 
 Ignition 62 
 
 Lubrication 55 
 
 Model B 63 
 
 Navy Type 58 
 
 Reduction of Vibration 53 
 
 Rocker Arms 56 
 
 Specifications of 51 
 
 Teardown 72-78 
 
 Lines of Force 35 
 
 Liquid Bodies, Law of 27 
 
 Lubrication, Effects of 24 
 
 Methods Used 24 
 
 Reasons for 24 
 
 Magnet, Electro and Permanent. . . 35 
 
 Magnetism 35 
 
 Magneto 41 
 
 Armature 41 
 
 Berling 41 
 
 Bosch 41 
 
 Dixie 42 
 
 Polar Inductor 42 
 
 Shuttle 41 
 
 94 
 
INDEX 
 
 Page 
 
 Sparks per Revolution 42-43. 
 
 Speed of Rotation 42-43 
 
 Timing : 48 
 
 Main Jet 29 
 
 Manif 9 lds 10,14 
 
 Materials of Construction 86 
 
 Mica 38 
 
 Mixture 27 
 
 Multi-cylinders 20 
 
 Ohm ... 35 
 
 Oil Duct 24 
 
 Oil Gauges 24 
 
 Pumps 24 
 
 Oil, Use of 25-26 
 
 Changing of 26 
 
 Oscillatory Current 38 
 
 Discharge 39 
 
 Overheating 22, 49, 90 
 
 . . 10, 14 
 
 Piston, Purpose of 
 
 Construction of 87 
 
 Piston Displacement 14 
 
 Piston Pin 10 
 
 Construction of 87 
 
 Piston Ring 87 
 
 Piston Travel, Measurement of . . . 45 
 
 Polar Inductor 42 
 
 Pop Back 15 
 
 Power Stroke 16 
 
 Power, Unit of 35 
 
 Power of Curtiss 83 
 
 of Hispano-Suiza 79 
 
 of Liberty 51 
 
 Power, Increase of 17, 19, 21, 30 
 
 Pressure Oiling System 25 
 
 Pressure Relief Valve 25 
 
 Primary Circuit 40 
 
 Interruption of 37, 44 
 
 Primary Coil 37 
 
 Primary Current 37 
 
 Propeller Alignment 19 
 
 Drive 18-19 
 
 Speeds 19 
 
 Thrust 19 
 
 Radiators 22 
 
 Regulator, Voltage 64 
 
 Tyrrel 64 
 
 Repairs 49, 88-89-90-91-92. 
 
 Emergency 49 
 
 Resistance 35 
 
 Retarded Spark, Reason for 47 
 
 Effects of 47 
 
 Retarded Timing 49 
 
 Page 
 Reversal of ' Flux ;, \ .V, .*,} < ^.38, 42 
 
 Rich Mixture, Effects of 34 
 
 Rocker Arm 14-18 
 
 Rotation, Direction of 46 
 
 Determination of 46 
 
 Rotary Pole 42 
 
 Rotary Shuttle 41 
 
 Secondary Circuit 40 
 
 Secondary Coil 37 
 
 Current 37 
 
 Shuttle 41 
 
 Spark Advance 47 
 
 Spark Plug 36 
 
 Spark Retard 47 
 
 Stroke 14 
 
 Sump, Definition of 14 
 
 Dry 24 
 
 "T"-Head 17 
 
 Teardown, Order of, for Liberty.. 72 
 
 Details of, for Liberty 73-78 
 
 Thermo- Syphon 23 
 
 Thrust Bearing . . 14 
 
 Timing Gears 14 
 
 Timing, Magneto . . . >. 48 
 
 Valves . . 44 
 
 Trouble Charts 88-92 
 
 Twelve-Cylinder Arrangement .... 21 
 Tyrrel Regulator 64 
 
 Vee Type Engine 21 
 
 Valve Action 44 
 
 Valve Clearance, Definition 18 
 
 Reason for and effect of 18 
 
 Adjustment of 46 
 
 Valve Closing 44 
 
 Valves, Exhaust and Intake 10-11 
 
 Construction of 87 
 
 Grinding 18 
 
 Location 17 
 
 Movements of 17 
 
 Opening 44 
 
 Operation, Chart of 44 
 
 Springs 14 
 
 Timing 44 
 
 Reasons for 45 
 
 Venturi 29-3C 
 
 Vibration 20,92 
 
 Voltage Regulator 64 
 
 Volt 25 
 
 Water Circulation 22 
 
 Water Cooling 22 
 
 Jackets 22 
 
 Pumps 23 
 
 Watt 35 
 
 95 
 
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