12

AUXILIARY ENGINES
A. GENERAL MOTORS 8-268 AND 8-268A ENGINES 12A1. General. The General Motors 8-
268 or 8-268A engine is used on board
modern submarines as an auxiliary
engine. It is located in the lower flats of
the after engine rooms, and may be
used for directly charging the batteries
or carrying the auxiliary load, and
indirectly for ship propulsion. The GM
8-268 is an 8-cylinder, in-line, 2-cycle,
air started engine rated at 300 kw
generator output at 1200 rpm. In
general, the individual parts of the
engine are similar to, but smaller than
the corresponding parts in the GM 16-
278A. For example, the camshafts,
exhaust valve and rocker lever
assemblies, injectors, pistons, cylinders,
liners and connecting rods are almost
miniature replicas of the 16-278A parts.
The main differences between the
engines appear in the construction and
design of the various systems such as

covers are of the safety type, each having
four spring-loaded plates, which in an
emergency, relieve any undue pressure in
the crankcase.
The main bearings are lubricated from
the lubricating oil manifold located in the
crankcase.
b. Crankshaft. The crankshaft is a heat-
treated steel forging finished all over,
having eight connecting rod throws or
crankpins 45 degrees apart. The
crankshaft is held in the cylinder block
by nine main bearing caps. The bearing
at the drive end of the engine acts as a
combination main and thrust bearing.
Lubricating oil is supplied under pressure
from a main manifold located in the
crankcase, and is forced through tubes to
the crankcase crossframes, where it flows
through oil passages to the main
bearings. From the main bearings the oil
flows through drilled holes, in the
crankshaft to the adjoining crankpin and
lubricates the connecting rod bearing.
The combination main and thrust bearing
journal No. 9 is not connected by drilled
holes to a crankpin. There is a 1/4-in.
diameter radial oil hole in the surface of
this journal into which a capscrew, with
the head ground off enough to clear the

Figure 12-1. Blower end control side of GM 8-268 auxiliary engine.
Figure 12-2. Blower end exhaust header side of GM 8-268 auxiliary engine.

231
Figure 12-3. Longitudinal cross section of GM 8-268 auxiliary engine.

232

Fi
gure 12-4. Transverse cross section of GM 8-268 auxiliary engine.

233

Figure 12-5. Cutaway of frame, GM 8-Figure 12-6. Lubrication of main
bearings, GM 8-268
268.
internal gear, cut in the inner bore of
the elastic coupling cover, meshes with
the crankshaft gear, forming a splined
drive connection to the crankshaft gear
which has a loose mounting on the
crankshaft.
The bearing bore of the crankshaft gear.
hub receives oil that flows from the

shell, and the flange so marked must be
toward the blower end of the engine. The
main bearing nearest the blower end of
the engine is the No. 1 main bearing.
Upper and lower bearing shells are not
interchangeable.
Crankshaft thrust loads are taken by the
rear main bearing. The thrust bearing
shells are the same as the other main
bearing shells except that the bearing
metal is extended to cover the flanges.
Each main bearing cap is marked with its
bearing number and is marked Blower
End on the side that should face the
blower end of the engine.
Lubricating oil enters the oil groove in
the upper shell through a hole in the top
and then 234
flows to the lower shell. The bearing
surface of the lower shell has an oil
groove starting from the joint face at
each side and extending partially
around the inner surface of the shell.
e. Pistons. The pistons are made of an
alloy cast iron. The bored holes in the
piston pin hubs are fitted with bronze
bushings. The outer ends of the bore for

The heated oil overflows through two
drain passages.
Each piston is fitted with six cast iron
rings, four compression rings above the
piston pin and two oil control rings
below. These rings are of the
conventional one-piece, cut-joint type.
f. Connecting rods. The connecting rod
is an alloy steel forging. The
connecting rod bearing in the lower end
of the connecting rod consists
cap. This is to insure that the backs of the
shells will be forced into full contact
when the cap is fully tightened. A drilled
hole in the lower shell fits on a dowel pin
in the cap. The dowel pin locates the
lower shell in the bearing cap and
prevents both the upper and lower shells
from rotating.
The piston pin is of the full floating type.
The piston pin bronze bushing is a shrink
fit in

Figure 12-7. Cross section of piston, GM 8-268.

235
the upper hub of the connecting rod.
The ends of the pin oscillate in the
bronze piston pin bushing hubs of the
piston.

to supply the cylinder with fresh clean
air, are located around the
circumference of the liner. When the
piston reaches the bottom of its stroke,
these ports are completely open and the
air space above the piston is charged
with fresh air.
The joint between the cylinder liner and
the cylinder head is made gastight by
an inner bronze gasket while an outer
copper gasket which has notches in it
serves to seat the head squarely against
the cylinder liner. The drain plug in the
lower part of the jacket of the cylinder
liner should be removed for draining
water when freezing temperatures are
expected and an anti-freeze solution is
not in use.
h. Cylinder heads. The engine cylinders
are fitted with individual cylinder heads
which are made of alloy cast iron.
Studs in the cylinder block hold each
head against the cylinder liner flange.
The joint between the head and the
liner is made gastight with an inner
bronze and an outer copper gasket. The
outer gasket serves to seat the head
squarely on the liner. The shallow
milled grooves show leakage of exhaust
gas or water.

236
through a bridge. Each of the valve
rocker levers is fitted at the valve end
with a nutlocked adjusting screw,
which has a hardened ball end that fits
into the ball socket in the valve bridge.
The injector rocker lever is fitted at the
injector end with a nut-locked adjusting
screw, which has a hardened ball at the
lower end. This ball is fitted with a
hardened steel flexibly mounted shoe.

the sequence of events essential to the
operation of the engine will be in the
proper order. The forged steel crankshaft
gear, which is driven by, the crankshaft
through the elastic coupling, is keyed on
a split collar and drives the camshaft gear
through the crankshaft and camshaft idler
gears. A spacer ring is doweled to the
crankshaft gear.
The shoe bears on the injector plunger
follower and transmits the rocker lever
motion to the injector plunger.
The rocker lever shaft is made of alloy
steel and is ground to size. The shaft is
clamped in the bearing support by two
bearing caps and is held in its correct
location by a dowel pin in one of the
bearings. A rocker shaft thrust plate is

j. Camshaft drive. In 2-cycle engine
operation the camshaft rotates at the
same speed as the crankshaft. The
camshaft drive gears are located at the
power takeoff end of the engine. They
transmit the rotation of the crankshaft
to the camshaft. It is necessary to
maintain a fixed relationship between
the rotation of the crankshaft and the
rotation of the camshaft so that
Steel-backed babbitt-lined bearing shells
support the inner and outer hubs of the
forged steel helical idler gears. The inner
and outer supports are bolted and
doweled together before being mounted
in the camshaft drive housing. The fuel
oil pump and governor are driven from a
gear that meshes with the lower idler
gear. A pair of bevel gears drives the
vertical governor shaft which is mounted
in ball bearings.
The lower idler gear also drives the quill
shaft gear, which is splined for the quill
shaft that drives the blower and accessory
gear trains. A splined coupling, which
rotates in the babbitt-lined center bearing,
joins the two sections of the quill shaft.
The overspeed trip weight assembly and
the camshaft gear are bolted and doweled
to a hub that also serves as a bearing

The accessory drive gear drives the
upper idler gear. This upper idler gear
drives the lower idler gear. A plate with
a splined hub for driving the lubricating
oil pump is bolted to the hub of the
lower idler gear. The fresh water and
sea water pump drive gears are driven
from the lower idler gear. The hubs of
the water pump drive gears have a
spline cut in the bore for the fresh water
and sea water pump shafts. The hubs
which project from each side of the
lower idler and water pump gears run in
steel-backed babbitt-lined bearings
mounted in the inner and outer bearing
supports. These bearing supports are
bolted together and the assembly is
fastened in place on the inside of the
accessory drive housing.
Lubricating oil is piped to the accessory
drive from the main lubricating oil
manifold in the cylinder block. Oil lines
and connecting pass ages in the bearing
supports supply oil to the bearings in
the drive.
The accessory drive cover should be
removed periodically and the gear train
inspected for excessive wear of any
parts. Lubricating oil lines and passages
should be checked periodically to

m. Engine control. The governor, which
is located at the generator end of the
engine, controls the engine speed for any
setting.
The movement of the governor power
mechanism is transmitted through lever
and link connections to the injector
control shaft in the cam pocket. Each fuel
injector rack is connected to a control
shaft lever through a slipjoint link. A
micrometer adjusting screw on this link
increases or decreases the amount of fuel
injected into the combustion chamber.
A slip joint is connected to each injector
rack so that in case the control rack in
one injector binds, the compression of
the spring in 238
the slip-joint link allows normal
operation of the other injectors. Each
spring is preloaded to limit the force
that can be applied by the governor to
move the injector control racks. When
the link is either shortened or
lengthened by a load greater than its
assembly load, the spring is
compressed.
The start and stop lever is used for

lock shaft in the cam pocket at each
engine cylinder. The injector lock
carries a lever on the shaft that moves a
pawl engaging a notch on the injector
rocker lever. The injection of fuel stops
when the locked rocker lever holds the
injector plunger at the lower end of its

filter on the cylinder head to a jumper
tube that supplies the injector. The
injector inlet contains another filter to
further prevent solid matter from
reaching the spray valve.
The surplus fuel is bypassed in the
injector and flows through another filter
in the injector outlet passage so that any
reverse flow of fuel cannot carry dirt into
the injector. The surplus fuel passes from
the injector through a tube to a fuel bleed
manifold, which is the bottom pipe in the
multiple oil pipe assembly. The fuel from
this bleed manifold flows to the metering
block, through the metering valve which
sets up enough resistance to maintain the
required pressure in the fuel supply
manifold, and then flows back to the
clean fuel oil tank.
Fuel oil leakage from the injector plunger
and bushing is drained through an
injector body ferrule, through a cylinder

12A3. Fuel oil system. a. Description.
The fuel oil pump draws oil from the
clean fuel oil tank and forces it through
the fuel block and the fuel oil strainer
and filter. From the filter, the oil flows
to the fuel supply manifold, which is
the third pipe from the top in the
multiple oil pipe assembly, and then
through a small jet
The pumping function of the injector is
accomplished by the reciprocating
motion of the constant stroke injector
plunger which is actuated by the injector
cam on the engine camshaft, through the
injector rocker lever.
The position of the plunger, and thereby
the timing, is adjusted by means of the
ball stud and lock nut at the injector end
of the rocker lever.
The quantity of fuel injected into each
cylinder, and therefore the power
developed in 239
that cylinder, is varied by rotating the
plunger by means of the injector
control rack. A rack adjustment (called
the microadjustment) located on the
control linkage permits balancing the

Figure 12-10. Cross section of Northern
fuel oil pump used on GM 8-268 engine.
or both filtering units. In normal
operation both filtering units are in
operation.
The arrows under the valve handles show
the positions of the valve handles for
using either one or both of the units. The
flanges are also marked IN and OUT
indicating the direction of flow of fuel oil
through the filter. When the valve
handles are between the two positions
indicated on the valve handle base, or
with the valve handles directly above the
inlet and outlet flanges, fuel oil is passing
through both units. If the valve handle on
the IN end of the filter is in one of the
positions indicated by the arrow on the
casting, the valve handle on the OUT end
Each pump gear is keyed to its shaft by
a pin.
f. Fuel oil strainer. The fuel oil strainer
contains two straining units, each with
an inner and outer winding. The space
between the windings on the inner and
outer elements is 0.001 in.
Fuel oil enters the strainer case, flows
through the outer and inner windings,
through the center of the elements, and
out through the strainer head. Provision

pump suction line. A spring-loaded
pressure relief valve is built into the
discharge passage of the pump body,
which bypasses excess oil into the
engine oil pan. The pump forces the oil
through the strainer and the cooler into
the engine lubricating oil system. The
engine inlet connection, on the blower
and pump drive housing, is fitted with a
spring-loaded relief valve. The spring
pressure is adjusted by means of a
regulating screw to maintain the correct
pressure. Any surplus oil is returned to
the oil pan.
Lubricating oil is supplied to the
lubricating oil manifold in the cylinder
block. From this manifold, oil is forced
through tubes to the crankcase
crossframes, where it flows through oil
passages to lubricate the main bearings.
The crankpin bearings are lubricated

upper connecting rod conduct lubricating
oil to the piston cooling chamber in the
top of the piston.
The camshaft drive gears are lubricated
with oil from the generator end of the
lubricating oil supply manifold in the
engine block. Oil is piped from this
manifold to the camshaft drive gear

the oil pan.
The blower and accessory drive gear
bearings receive oil from the blower
end of the lubricating oil pressure
manifold in the engine block. Oil for Figure 12-13. Cutaway of lubricating oil
cooler GM 8-268.
draws the oil from the camshaft drive
housing and returns it to the engine oil
pan. The generator bearing scavenging
pump draws the excess oil from the
generator bearing and returns it to the
engine oil pan. The pump housing is
made in four separate parts: the bearing
flange, the generator bearing scavenging
pump housing, the camshaft drive
housing scavenging pump housing, and
the lubricating oil pressure pump