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A Study of the Design of a Four Cylinder
Overhead Camshaft Motor

A Thesis Submitted to the Faculty of the
Michigan Agricultural College

By

J.0.Barkwell

Candidate for the Degree

of

Bachelor of Science
THESIS
This subject was chosen because of the lack of
overhead camshaft motors on the market and the chance for
developement along this line. This design has fewer parts,
less lost rotion in valve operation, and can therefore be

easily and chaaply built.

A motor of this type can be built which will
embody strength, econony, durebility, and accessability
Without eliminating those features which cost more to
manufacture, but which are necessary to the long life

and cheap maintenance of a motor.

It is the writer's idea to design such a motor

and the data is to be found on the following pages.

93847
General Description of the Motor.

The motor is four cylinder, four cycle type. It
has a bore of three and one eighth and a stroxe of four and
one quarter.inches. The motor is of the overhead valve type
with a detachable head which carries the camshaft. The canm-
shaft is removable with the head and is remcvable from the
head by removing ten cap sorews. It is rotated by means of
a special silent chain which has a stream of oil running on
it at all times. The valves are unusually large allowing an
easy flow of gases in and out of the cylinders. The valve
etexzs are large allowing a large radiation surface which
prevents valve stickase. The valves are operated by camaon
arms Which are pivoted on one end and are adjustable on the
other end to take up the play between the valve stem and the
arm. The head and block are of semi-sateel. The head is held
to the block by fourteen cap screws. The crank shaft is large
with large bearing surfaces and has three main bearings. The
end bearings are three inches long and the center bearing is
two inches long. The piston pins are extra.large and are
connected rigidly to the connecting rode and are floated in
the piston. The pistons are cast iron and are longer than the
averase piston cf this size. The pump and generator are run
thr u bevel cut spur gears. The o11 pump is run from the
crankshaft by means of spiral gears. The flywheel is geared

to accomodate an electric starter.
 

 

Carburation.

The motor ia desi,pned to use a twin manifold.
The intake part is cast on the inside to receive as
mich heat as possible. It is designed to take a one inch
carburator. The manifold is made to take any standard
carburator and is a matter of choice tetWeen manufacturers.
The manifold ia held to the block by four studs. The

carburator sets up high where 1t is easily accessable.

Ignition, Starting and Generation.

This motor is designed to use a standard S.A.*F.
mounted dynamotor. This contains a starter, generator and
ignition. The plugs are placed in the side of the block
and are easily removable.

Cooling System.

The cooling syatem is of the pump type. The pump
ig lecatea at the bottom of the block end takes the water
from the bottom of the radiator and circulates it thru the
motor. The pusp is of the multi-vane type centrifugal pump.
It revolves at enzine speed. A fan is provided to draw air
thru the radiater and revolves at tito times engine speed.
The Water pockets are larze and 2ll parts receive ample
cooling. The circulation will te very rapid. The water pass-

ea out at the side of the head.to the radiator.
Compreasion and Clearance.
The S.A.©. Journal gives the follewing values of

nas used in the calculation cof compression pressures.

Initial preseure absolute lli# n is 1.21
Initial pressure absolute 137 nis 1.99
Initial preasure absojute 14 nie 1.34

The initial pressure will vary vith the speed of
the motor. The higher the speed, the lover the initial
pressure. This is caused by the increased friction in the
valve pockets and inlet pipe.

Favary gives a table of compression pressures
for each of the above mentioned initial pressures for
varicus compression ratios.

The ratic used on this motor is 5 to 1, count-
ing the chamber as one part and the displacement volume ag
four parts. For llg# the final pressure is S0#; for 13# it
ig 1054; for li# it ie lol#. It ig held that thie mctor
Will be reasonably high speed and 134 is taken as being the
probable initial pressure.

The stroke of the motor is 44" and the compress-

ion space is 11/16".
Cylinder Dimensicns.

Thies motor is designed to drive a two thousand
Found car. It is estimated that a motor of ten horsepower
S.A.E. rating will be powerful enough for the work. The
S.A.E. rating of a motor is equal to the produet of the
bore squared and the number of cylinders divided by a
constant 2.5 which the Society has arrived at after much © .:-
experiment. This holds true for 1000 piston f.pem.

This motor develops 10.6 h.p.e and as it is of
overhead valve construction, twenty percent more power
may be relied upon. This data is given in teste run by the
Euick Motor Co,

The bore-etroke ratio is 1.36. This is smaller
than the ratio recommended by Favary, but is thot to be
sufficient to develope the required power and it is a
known fact as given out in the above mentioned test, that
the longer the stroke the less economical the motor is.

Thickness of walle equal .045 bore plus .063
plus 1/16" for irregularities in the casting. A 5/16" wall
Was used.

Thickness of water jacket walle equals 1/8" plus
1/32" for each 3" over 2% Use 1/4",

Thickness of jacket equale .437 plus (Bore-3).125
A water jacket 4" thru was used with i" between the pairs
of cylinders. A large water pocket is placed in front to

form a support for the head.
The head is bolted to the block and the walle are
rade thicker at these pointe. Large water spaces are left
arcund the valve pockets. It was ne@essary to extend the
block in the front 6o as to support the head which is
long in front to take care of the camshaft bearings. A heavy
Copper gaeket is placed between the block and head.

Valves.

The valves are located in the head because of the
economy, accessability, poWer, and seize of motor necessary
per horsepower. These advantazges are set forth in a pamphlet
published by the Buick Motor Co. The valves are 1 7/16" in
diameter with a mean effective diameter of 1 1/4". The stem
is 3/€" in diameter. The valves are as large as possible in
this size of motor. The large stem prevents sticking, conducts
heat away readily, and forms a large wearing surface. The
suides are 1 2" long and are pressed into the block thr a
thin shell which allows good cooling. The guide is chan:e-
able and is longs enough to prevent rapid wearing.

The valve springs are calculated by a method given
by Clark. Assume the valve gear weight equal to 1 pound. The
valve cust open 9/32". This is given by Favary as equal to
.125(Mean Dia.-1.95") plus .281". The motor speed is 2000
rep.M and the time of closing valve on the cam is 40 degrees.
Los. Required equals the product of the weight and the
ancular velocity squared and the radius of the crank. This
equals 69.24. Use 70#. This is the force necessary to close

the valve.
The diameter of the spring wire is equal to the
cube root of product of the pounds required and the mean
diameter of the spring divided by .39 of the permissible
stress.

One inch was taken as the mean diameter of the
coil, the weight required wes taken as 70#, 70,000# is
the required stress.

Wire No. 10, “Yashburn & Moen Guage is .135"
in diameter and will fill the requirements.

Deflection per coil the product of eight times
the weight in pounds required and the mean diameter of the
coil cubed divided by the allowable stress multiplied by the
Wire dianseter to the fourth power.

Deflection per coil is .131".

Add 25% for the maximum stress that will come on
the coil and take that ratio times the deflecticn. The
maximum deflecticn that will result ia .163".

The product of the number of free coils by the
difference in the two ceflections is equal to the lift of
the valve.

~163-.131 equale .o%. This gives the number of
free coils ag J.

The spring rests on the head of the motor and is
held in place by the spring caps and a pin thru the head

or top of the stem.
Camshaft.

The camshaft is carried on the head of the motor
and is driven by a silent chain off the crankshaft. The
shaft is +# in diameter at the bearings and at the cam

bottoms. It is 11/16" tetween these pints.

It is suspended on three bearings of sufficient
length to prevent whipping. It is driven from the crank-
shaft by means of tWo gears and a silent chain. The ratio
ie 2 to 1 and the gears have 25 and 50 teeth. The distance
between centers is 20". The amount of poWer required to turn
the shaft is not readily obtainable but is estimated as being
under} hep. A chain 3/2" pitch, 3" wide and 50.85" long
will carry the necessary load. The gears are 5.9/7" and 2.99"
in diameter and have a face 1 1/32" wide. The gears are
equipped with wire olips to keep the chain lined up. The
above data was taken from a hand beok sent out by the Link
Belt Co., manufacturers of silent chain. The shaft ia
hollow and each cam nas a hole drilled in it eo as to oil
the arm and valve mechanism, as well as the cam bearing
surface, The cam acts on an arm which is suspended from the
valve stem to the arm holder. The cam acts at the center and
therefore needs only one half the eccentricity usually
reguired. This amounts to 9/64". The arm holder is large
and will allow a large amount to wear off befor e rebusahing
or other edjustment is necessary. An adjustment is previded
on the valve end to allow for adjustment betveen the arm and

aten. This should te not over ten thousands. The vapor thron
out of the cam lubricatea this point. The vapor is condensed
and carried back to the base thru a drain pipe. The cam shaft
can be removed by removing ten cap screws and the chaincase
cover and chain. Wear in the chain may be taken up by placing
pressed steel shims uncer the head. This will chahbge the
combustion chamber and compression but not enough to make
any difference in the preformance of the motor. The tendengy
of the camshaft is to draz while the tendency of the crank
shaft is to pull and the driving side of the chain will
always be tawt. It is estimated that a 50" chain will not
wear or etretch over 4® Ina cear 6" in diameter this
means a difference in opening and closing of less than five
degrees. Manufacturers vary in this respect from twenty to
twenty five dezreesa and a matter cf five degrees will make
practically no difference. The gears ere keyed to their
respective shafts and suitable provision is made to remove t
them easily if necessary.

Cams.

The cams are opened and clesed by means of Simple
Harmonis ¥Motion. The intake valve is opened in forty décrees
on the cam, remains open fifteen desrees and cleses in
forty mere.

The exhaust valve opens in thirty degrees on the
cam, remains open for forty five der-rees on a tangential

face, and cleses in thirty decrees.
The intake valve opens 10 degrees past upper dead
center. It is wide open at 90 degrees past upper dead center
and remains open for 30 degrees. It takes eighty degrees to
Close at 20 degrees past lower dead center, making a total
of 190 degrees.

The exhaust valve opens at 30 degrees before lower
dead center, takes 60 degrees to open fully, remains open
for 90 degrees, and closes futly in 60 degrees at upper
dead center, making a total of 210 degrees for the operation.

It is necessary to leave the exhaust valve open
for a long period so as to completely scavange the cylinder
and leave it clean to receive the new charge. Some manufact-
urers fail to observe the fact that the exhaust gases do not
flow out as readily as the intake gases and make no difference
in the shape of the cams. These motors lack in power and
acceleration.

Piatons.

The pistons are made of gray cast iron, have four
rings, and are reenforced by rings of metal on the inside
behind the ring grooves and at the bottom. The wall is 1/8"
thick, carrying this dimension behind the ring grooves.as
well. The rib at the bottom is 1/16" thicker. The rings used
are 3/16" wide. The nead is 3£16" thick at the center and
tapers at the sides to 4", The boss diameter varies from 1}"
at the wall to 1 3/6" at the inner end. The boss is forty
percent of the distance from wall to wall. The boss carries
the piston pin bushings which are 7/&" inside diameter. The
piston is made long to prevent slapping. It is 4 1/16" long.

The lower ring is a scraper to carry away the extra oil and
it alao helpa to prevent piston slap. The pin boss centers
are off set because of placing the spark plug in the side
of the block. This is done so asa to make the side opposite
the plug heavier. This extra weight helps to balance the
force of the explosion which occurs eatlier on the spark
Flug aide. The amount of this offset will have to be deter-
mined by experiment. With a long piston this offset will not
be very great.

Piston Pins.

The piston pins are 7/8" in diameter and 3" long.
Thay are floated in bronze bushings in the piston and are
held stationary in the connecting rods. The piston pin is
slotted at the end so as to allow a place to turn the pin
to line up the cap screw gpoove. The pin is drilled hollow
to a dimension .65 the outside diameter. It is casehardened.
Jany manutacturers to-day are fastening the pin in the piston
and floating it in the rod. By doing this they are cutting
the bearing surface almost in half. It is done because it
is chaaper to build and easier to change, but thie type
must be changed more tham twice as often.

Connecting Rods.

The connecting rods are dro forged steel with
lar;e bearing surfaces. The lower end is made to fit the
2" crankpins, The upper end to fit the 7/%" pins. The rod
is made 2.12" times the stroke. All corners are rounded
and five degrees draft is allowed. Favary gives a chart
of dimensions for I sections of connecting rods. From this
chart the following data is obtained,

Total width at center Zn
Breadth 19/302"
Width of web at center 1/on

Width of flange 1/8"
Thickness of web 1/8"
Length of rod gr

The rod is two inches wide at the bottom and two
and three quarters wide center to center of the bolts. The
bolts have @ round head with one side ground to fit the
shoulder of the connecting rod. This isa non-turnable. These
bolts are fitted with lock washers and nuts, and with cotter
keys. The bearing metal is 3/16" thick and is cast in the
rod being held in place by the metal in depressions drilled
in the rod and cap. |

Balancing of Motor.

Three types of crankshaft may be used for a four
Cylinder motor. Two, three, or five main bearings may be
used. Two bearings are usually not enough to keep the
shaft from whipping and are easily loosened. Thres bearings
shafts are always in atatic as well as running balance.

Five bearings are seldom used except for truck motors or
other heavy duty motors. Three bearings were used in this :
Cage.

Crankshaft.

The diameter of the crankshaft as given by Favary
is equal to the square root of a cylinder diaplacement
divided by 16. The displacement is 32.5 cu.in.e per cylinder.
This gives a shaft 1 7/16" in diameter. A 2" shaft was
used. The thickness of the arms is equal to the product of
the square root of the diameter cubed divided by the
Width of the crank arms and .6 or .& according to which arm
is being figured. The larger Constant is used for the long
arm, The width of the arms is equal to 11/8 times the
crank pin diameter. The thickness required is .65" and .87"
for the short and long arms respectively. 1" and 1 5/16"
Were used. The orankehaft is 2" over all and the flange
for the flywheel isa forged intecral. The front end carries
the gears for the auxiliary drive and these gears are keyed
on With Woodruff keys. It ia threaded on the front end and
drilled for pine to carry the crank hook which has the oil
pump gear cut on it. The three main bearings are extra
long and contain a greater area than ia necessary. The frost
and rear bearings are three inches long and the center is
two inches long. The total bearing area is 503 sqein. and
only 30 aq.in. ia required. The larcger the bearing surface
the longer the bearing will run without adjustment.

Flywheel.

By a comparison of displacements it was found that
a motor of 130 cu.in.e displacement would require a flywheel
of approximately 50# weight. The mean radius was zgoverened
by the size of the housing and was taken asa 5", Having the
Weight, mean radius, and assuming a thickness of two inches,
the width:was eolved for. It is three inches. The cubical
content is 192 ocu.in. No allowance is made for the weizcht of
the flange or the Web. “xperdmental work is required to
find the weight of the wheel exactly. The radius of the
wheel must be given considerable attention. The type of
‘Glutch ia a very important factor in the design of the wheel

ag it is necessary to design the wheel to fit the clutch.
A disc clutch could be easily used with this flywheel,

It is necessary to use a flywheel large enough to prevent
vibration and to carry the motor over to the next firing
position. If the flywheel is to large the motor will
pick up slowly and if it is to small there will be quite
considerable vibration. The ideal flywheel is one that
will allow fast acceleration and smooth vibrationless
running. It can be easily seen that this may reyuire a
great deal of experimental work.

Crankcase,.

The crankcase ia made in two parts divided on
the Centerline cf the main bearings. The upper half is
made of aluminum and varies from 1/4" to 3/8" in
thickness. The parts carrying the most atrain are built
-thick and are "ell braced. This half has a pum bracket
and a place to mount the dynamtor. The flywheel cage
ia cast intezgral with this half. A wall extends .across
the case at the center bearing. The left side is clear
except for a breather tube thru which the case is filled
With oil. The motor is a three point suspension and the
tvo rear points are carried on extensions of the flywheel
housing. A plate is provided on the top of the flywheel
case which may be sWung to the side to allow a clear view
of the flywheel for timing the motor. The studs which
hold the block are carried in extra large bosses, and
there are eight of them.

The lower half is pressed steel 1/8" thick and
carries no strain, but acts as an oil retainer and a

protection to the movins parts.
The gears are lubricated by revolving in a pool
formed by welding a baffle plate directly behind them. As
the pool fills with o11 from the chain above, the oil runa
over into the case. There are four trouzhsa for the rods
and an o11 gage case is welded on. This half is bolted to
the aluminum half by means of cap screws, The lower half
of the flywheel housing is cast iron and is bolted to the
aluminum and over the back end of the pressed steel half,
This forms an absolutely rigid joint.

Auxiliary Drive.

The gears which drive the camshaft and pumpahaft
are keyed to the crankshaft by means of Woodruff keys.

The inside gear drives the camshaft thru a silent chain and
sear. The outaide gear propels the pump and generator shaft
The data for the silent chain is given in another part. The
zZeare driving the punp and senerator are of equal size, 56
teeth, € pitch, and /(" in diameter. One of these gears is
steel , while the other is fiber with steel faces on either
side but not running steel to steel. The fiver is the same
Width as the steel. The pump shaft is 5/8" in diameter and
is fitted with joints between the case and pump and pump
and dynamotor so as to allow easy removal of either. The
impeller is pinned to the shaft sand is enclosed in a case
fith a removable head.

Fane

The fan ia four bladed, 134" in diameter. It is
driven by means of a belt i" wide. It is supported on the

front end of the crankcase and a spring and adjusting ecrew
are provided to keep the slack out of the belt. The fan is
mounted on ball bearings and the hub is hollow and carries
oil for lubrication. The pulleys are two and four inches in
diameter and this gives a ratéo of two to one. The fan
rotates at twice engine speed. This gives three thousand
repem. allowing for twenty-five percent slippage. The fan
ha3 a capacity of about 2/00 cu.ft. of air per minute.

Lubrication Syaten.

The lubrication ia a combination splash and pressure
system. The case ia drained into a pipe and carried to the
pump which is mounted on the front of the crankcase and is
driven off the crankshaft. The pump is of the friction gear
type. The oil inlet is above the.line of mesh of the gears
and the outlet is below at one end. The pump is always
primed by means of a ball and spring placed in the line from
the case to the pump. This closes when the force of the pump
is etopped and the oil can not flow back to the base. Three
leads carry the oil to the base, thechain, and the camshaft.
lost of the oil is carried to base and déstributed to the
Connecting rod sumps. The splash from these lubricates the
cylinder walls and fills the main bearing pumps. Another
lead carries the olltto the camshaft which is hollow and
each cam is drilled to allow oil to get to the valve mechanism.
The third lead carries the gil to the top of the chain case
Where it runa directly 6a the chain and fills up the sump
at the bottom in which the gears rotate.
The pump is driven by means of a spiral gear which is pinndd
to the shaft and is easily resovable and changeable. The
case holds five quarts of oil and is drained by removing the
plug at the bottom where the pump lead is fastened.

The size of tne pump can be determined only by

experiment only after the amount of oil per minute is

em,

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determined.
In the foregoing pazes, the vriter has endeavored
to give a good preliminary desizn of a light four cylinder
motor. Such data as ia necessary is given and calculations
are made Wherever possible. If tnis motor were to be
manufactured it would undoubtedly be necessary to change
it considerably before placinz it on the market.

The writer believes thease ildeas and deaizns are
fundamentally good. It is believed that as the over—head
valve motor increases in popularity as it is doing, tnat
manufacturers “ill be looking for a cheaper, easier means
of operating valves and that the over-head camshaft will

eventually come into popularity.
The writer oWes much to the cheerful aid and
splencid agsiastance extended him in his work by

Profeasgors Field and Hewlett.
 
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