BASIC BLOCK
SYSTEMS OPERATION
TM 5-3805-263-14&P-2
BASIC BLOCK
CYLINDER BLOCK
The cylinder block has four cylinders arranged in-
line. There are five main bearings that support the
crankshaft. Thrust bearings installed on the rear
main bearing web control the end play of the crank-
shaft.
The cylinder block has cylinder liners that can be
replaced. The top surface (deck) of the cylinder
block is the support for the liners. A spacer plate, that
goes between the cylinder block and the head, is used
to eliminate the need to counterbore the block for the
liner flange.
PISTONS, RINGS AND CONNECTING RODS
The cast aluminum piston has three rings; two
compression rings and one oil ring. All rings are
located above the piston pin bore. The two compres-
sion rings are of the KEYSTONE type and seat in an
iron band that is cast into the piston. KEYSTONE
rings have a tapered shape and the movement of the
rings in the piston groove (also of tapered shape)
results in a constantly changing clearance (scrubbing
action) between the ring and the groove. This action
results in a reduction of carbon deposit and possible
sticking of rings.
The oil ring is a standard (conventional) type and
is spring loaded. Holes in the oil ring groove provide
for the return of oil to the crankcase.
The piston pin bore in the piston is offset (moved
away) from the center of the piston 0.76 mm (.030
in.). The full floating piston pin is held in the piston
by two snap rings which fit into grooves in the piston
pin bore.
The piston pin end of the connecting rod is tapered
to give more bearing surface at the area of highest
load. The connecting rod is installed on the piston
with the bearing tab slots on the same side as the “V”
mark on the piston.
CRANKSHAFT
The crankshaft changes the combustion forces in
thecylinder into usable rotating torque which powers
the machine. There is a gear at the front of the
crankshaft that drives the timing gears and the en-
gine oil pump. The connecting rod bearing surfaces
get oil for lubrication through passages drilled in the
crankshaft. Lip seals and wear sleeves are used at
both ends of the crankshaft to control oil leakage.
1-20
