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
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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
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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
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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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92
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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