TM 5-4320-218-15
29 Cap screw
25
Shim (0.014 -in.)
21 Starting crank
17 Oil slinger
30 Oil seal
26
Gasket (0.003 -in.)
22 Shim
18 Flywheel
31 Connecting rod bolt
27
Bearing plate
23 Palnut
19 Lockwasher
24 Shim (0.006 -in.)
28
Lockwasher
20 Nut
Figure 33-Continued
Note. Each pistion and connecting rod is marked
b. Wash all parts in an approved cleaning
for its cylinder; make sure that the parts are assembled
solvent; dry thoroughly.
in the proper position.
c. Measure the cylinder bores with an inside
b. Place the proper connecting rod (8) in
micrometer. Measure the bore lengthwise and
the matched piston so that the stamped arrow
crosswise above the ring travels; repeat the
on top of the piston faces the side of the con-
measurement at the top of the ring travel. The
necting rod opposite the oilhole in the con-
difference in these measurements will deter-
necting-rod cap. Tap the piston pin into the
mine the amount of wear in the cylinder bore,
other bore of the piston, and install the two
the taper, and out-of-round condition. If cyl-
retaining rings (6).
inder bores are worn more than 0.008 inch,
c. Expand the oil ring (3), and install it in
rebore the cylinder with conventional reboring
the bottom groove of the piston skirt with the
equipment and hone until the bores are not
scraper edge of the ring facing toward the bot-
more than 0.001 inch out-of-round, and are
tom of the piston. Next, install the scraper
not tapered more than 0.001 inch.
ring (2), and finally the compression rings (1).
Caution: Before boring or honing the
The scraper ring also has a scraper edge; the
cylinder, wrap the crankshaft with rags to
ring must be installed with the edge facing
protect its bearing surfaces from abrasive
down. Stagger the ring and gaps on the pis-
particles. Measure the cylinder frequently while
tons.
honing to keep from honing the bore oversize.
d. Fit the connecting-rod bolts (31) in the
rod, and fit the upper bearing half (9) so that
d. Clean the carbon from the top of the
oilhole in the bearing alines with the oilhole in
piston. Clean the ring grooves with a ring-
groove tool or a piece of an old ring.
the rod. Lightly oil the piston, piston rings,
and cylinder walls. T u r n the crankshaft so
e. Wash all of the parts with an approved
that the crankshaft journal to which the rod is
cleaning solvent, and blow dry with com-
to be attached is at top dead-center. Use a ring
pressed air.
compressor to compress the piston rings.
f. To measure the piston-ring gap, place the
Note. When installing the pistons in the cylinders,
ring into the cylinder bore in the approximate
install the pistons so that the arrow on top of the piston
operating position, and measure the gap with
points in the direction of crankshaft rotation. Piston
and connecting rods must be reassembled into the same
a feeler gage. The gap clearance should be be-
cylinder bore from which they were removed.
tween 0.010 to 0.020 inch. If the ring is too
small, use an oversize ring. If the gap is too
114. Installation of Connecting Rod
small, clamp a file in a vise and position the
and Piston
ring on the file with the file in the ring gap,
a. Lower the pistons into the cylinders as
Lightly squeeze the ring together and move it
outlined in the above note. Using the butt end
back and forth to file both ends at one time.
of a hammer handle, carefully push the piston
Measure the gap frequently to keep from fil-
and connecting rod into the cylinder until con-
ing off too much stock.
necting rod rests on the crankshaft. This ac-
tion will release the piston-ring compressor.
113. Reassembly of Connecting Rod
and Piston (fig. 33)
b. Assemble the lower bearing half (9) to
the cap so that the oilholes aline. A number is
a. Using a fiber hammer, tap the piston pin
s t a m p e d on each rod and cap to insure
(5) into the piston (4) about 1 inch.
