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TM5-4210-229-14&P
6-12. PISTON AND CONNECTING ROD MAINTENANCE (Continued).
(1) Running clearance check (using virgin lead
wire).
(a) Remove bearing cap, then clean and oil
the crankshaft journal.
(b) Place a suitable length of 0.010 in
(0.254 mm) virgin lead wire across the
bearing then install the bearing cap,
torquing nuts to 115 ft-lb (155 N.m).
(c) After torquing nuts, remove them along
with the bearing cap.
(d) Remove the virgin lead wire which will
have been crushed down to the amount
of clearance between the crankshaft
journal and the connecting rod bearing.
(e) Measure the crushed wire with a
micrometer to determine running
clearance.
(2) Running clearance check (using plastigage).
(a) Remove bearing cap, then clean the
bearing surface and exposed half of the
crankshaft keeping them free of oil.
(Plastigage is soluble in oil).
(b) Place a piece of plastigage (Appendix
D, Item 40a) across the bearing then
install the bearing cap, torquing nuts to
115 ft-lb (155 N.m).
(c) After torquing nuts, remove them along
with the bearing cap.
(d) The flattened plastic material will be
found adhering to either the bearing
shell or the crankshaft. Do not remove
the Plastigage.
(e) To determine the running clearance,
compare the width of the flattened
plastic material at its widest point with
the graduated marks on the envelope.
The number within the graduation on
the envelope indicates the clearance in
thousandths of an inch.
(3) Running clearance check procedure.
(a) The measurement should fall within
0.0018 to 0.0051 in (0.046 to 0.130
mm). Remove the test material and re-
install the cap and bearing with correct
torque if running clearance specifica-
tions are met.
(b) Repeat the chosen method of testing
for all the remaining connecting rods.
(c) If the measurements are not within the
specified limits, and the torque wrench
is known to be accurate, remove the
bearing from the connecting rod and
replace it with a new bearing.
(4) Check connecting rod end clearance, using
a feeler gauge. Maximum permissible bear-
ing end clearance on crankshaft is 0.018 in
(0.46 mm).
(a) The feeler gauge must cover both the
connecting rod and cap.
(b) Excessive clearance may require re-
placement of the rods or shaft.
(c) The check must be made to be certain
that the specified clearance exits.
(d) Lack of clearance could indicate a
damaged rod or perhaps a rod bearing
out of position.
c. Pistons and rings inspection.
(1) Soak the piston and piston pin in soap solu-
tion (until carbon is soft) and clean
thoroughly.
6-31
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