TM 9-2320-272-24-4
5-10. PISTON AND CONNECTING ROD MAINTENANCE (Contd)
7.
Using telescoping gauge, measure inside diameter of crankshaft. journal bore (2) in connecting
rod (1) at points A-A and B-B, up to 30 either side of parting line C. Record readings. If crankshaft
journal bore (2) diameter is not 3.2725-3.2730 in. (83.122-83.134 mm), replace connecting rod (1).
8.
Using telescoping gauge, measure inside diameter of crankshaft journal bore (2) in connecting rod
at points D-D and E-E. Record readings. If crankshaft journal bore (2) diameter is not 3.2725-3.2730
in. (83.122-83.134 mm), replace connecting rod (1).
NOTE
Check pin bores with bushings installed.
9.
Check inside diameter of piston pin bushing bore (6) in connecting rod (1) with telescoping gauge. If
piston pin bushing bore (6) is worn beyond 2.0022 in. (50.856 mm), mark bushings for replacement.
NOTE
l Pistons must be cleaned before inspection.
l Conditions of the pistons and piston rings should be carefully
noted, as `they indicate borderline conditions leading to engine
failures.
l Pistons should be inspected at ambient temperatures of 70-
90F (21-32C).
10.
Check piston (5) wear surface for scoring, scuffing, and cracks. If scored, scuffed, or cracked, replace
piston (5).
NOTE
Vertical scratching and discoloration of piston ring sealing surface
is a major cause of oil consumption and piston and liner scoring.
11.
Check piston rings (3) for vertical scratching and discoloration of piston ring sealing surface. If ring
sealing surface is scratched or discolored, replace piston rings (3).
12.
Check for broken piston rings (3). If broken, replace piston ring (3).
13.
Check piston rings (3) for formation of deposits which prevent outward movement of piston rings (3) to
seal. If piston ring (3) sticks in piston grooves, replace piston ring (3).
14.
Check piston pin bore (4) on piston (5) for fractures. If piston ring bore (4) is fractured, replace
piston (5).
NOTE
l Pistons must be inspected at ambient temperatures of 70-90F
(21-32C) to obtain accurate measurement readings.
l First and second piston ring grooves are checked for depth wear
the same way. Step 15 checks for ring groove depth wear on the
top ring groove.
15.
Insert ring groove gauge into top ring groove (7) of pistons (5) and note whether shoulders (6) of
gauge touch ring groove (7). If shoulders (6) of gauge touch either ring groove (7), pistons (5) are not
serviceable and must be discarded.
16.
Repeat step 15 for second ring groove (8).
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