TM 5-6115-400-35
gamble of reinstalling bearings with
undetected fatigue, and also to
prevent accelerated fatigue which
may develop from a minute
repositioning when reinstalling the
used bearings.
(2) Connecting rod piston pin bearing
replacement. If the connecting rod piston
pin bearing (fig. 91) is worn, it must be
pressed out and a new bearing pressed
into the connecting rod.
When new
bearings are installed, be sure oil hole in
bearing-lines up with rifle-drilled hole in
connecting rod. The specified diameter of
a new piston pin is 2.0015 inches-2.0017
inches, and inside diameter of the bearing
is 2.0027 inches-2.0033 inches; this
provides a clearance of .001 inch-.0018
inch between pin and bearing. It will be
necessary to ream connecting rod to
obtain this clearance. The bore in piston
for the piston pin is 2.0018 inches-2.002
inches
(cold, providing a pin-to-bore
clearance of .0001 inch-.0005 inch).
58. Main Bearing Caps
a. General.
(1) Replacement caps for front, intermediate,
and rear bearing locations are machine
finished except for the bore which is semi-
finished. The replacement center cap is
machine finished except for the bore and
Figure 94. Checking connecting rod alinement.
the thrust faces.
Note.
(2) Main
bearing
caps
are
not
interchangeable, and if replacement
Never file or shim the bearing caps to
becomes necessary, new caps must be
make the bearings fit; install new
machined in place. To maintain correct
bearing shells if the fit is
alinement and size in the main bearing
unsatisfactory. The crankshaft must
bore in the block, caps must be installed
turn freely after all the connecting
to the specified torque before machining.
rod nuts have been tightened to the
Replacement of main bearing caps in a
specified torque.
machine shop job.
(i) As a general recommendation, it is
b. Main Bearing Cap Replacement.
more practical to replace connecting
(1) When it is necessary to do any machining
rod bearings whenever they are
to the main bearing bore in the block, it is
removed from the engine after
important that the center line of the
2,000 to 8,000 hours of service than
crankshaft is not altered from its original
to reuse them. The cost of new
center line, especially at the timing gear
replacement bearings will offset the
end.
128
