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ENGINE
PISTONS-RODS
2-37
2-23 REPLACEMENT OF PISTONS,
RINGS, AND CONNECTING RODS
a. Removal and Disassembly of Piston and
Rod Assemblies
1. Remove cylinder head
(par.
2-16), dis-
connect tie rod from pitman arm and remove
lower crankcase, remove oil pump.
2. Examine the cylinder bore above the ring
travel. If bore is worn so that a shoulder or
ridge exists at this point, remove the
ridge
with
a ridge reamer to avoid damaging rings or
cracking ring lands in piston during removal.
Chamfering at 15 degrees angle will prevent
ring damage when pistons are reinstalled. See
figure 2-32.
Figure 2-32-Removing Ridge from Cylinder Bore
3. Remove caps and push piston and con-
necting rod assemblies out of cylinders, using
care to prevent rod bolts from contacting and
nicking crankshaft journals. Make sure that
connecting rods and pistons are properly num-
bered so that they can be reinstalled in original
locations. It is advisable to reinstall ca ps on
rods to avoid mixing parts or misplacing
shims.
4. Remove Flex-Fit oil rings, then remove
other rings from pistons. Rings may be removed
Figure
2-33-Removing
Pist o n Ring
without danger of distortion or breakage by use
of Ring Remover KMO 297-E (Series 40-50) or
KMO 297-D (Series 70). See figure 2-33.
5. Remove the piston pin clamp
screw.
Do
not clamp the connecting rod in a vise for this
operation as the rod may be twisted out of
alignment if clamp screw is very tight or vise
jaws are not square. After removal of clamp
screw, tap the piston pin through rod and
piston with a fibre or brass drift; a hard steel
punch may damage the parts.
b. Inspection of Cylinder Bores
Engines are marked in production with color
codes to indicate exact diameters of cylinder
bores and pistons to aid in selective fitting of
pistons on the assembly line. Code markings
are placed on cylinder crankcase lower flange
opposite each cylinder bore and on bosses inside
the pistons. These color codes have no value in
service since replacement pistons cannot be
supplied according to color codes and usually
some change has taken place in cylinder bore
dimensions after the engine has been in service
for some time.
Inspect cylinder walls for scoring, roughness,
or ridges which indicate excessive wear. Check
cylinder bores for taper and out-of-round by
means of an accurate cylinder gauge placed at
top, middle, and bottom of bore both parallel
and at right angle to center line of engine. See
figure 2-34. The diameter of cylinder bore at
any point may be measured with an inside
micrometer,
or by setting
the
cylinder gauge
Figure 2-34-Checking Cylinder lore with Gauge
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