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Page Title: Figure 6-44. Typical Bearing Failures.
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TM 10-3930-633-34
twisted rods will disturb the action of the entire
6-32. Main and Connecting Rod Bearings
piston, rings, and connecting rod assembly and
Cleaning and Inspection
may be the cause of excessive oil consumption.
a. Cleaning. Clean the bearing inserts and caps
(5) Inspect the connecting rods for signs of
thoroughly in solvent, and dry them with com -
fractures and the bearing bores for out-of-round
pressed air. Do not scrape gum or varnish
and taper. If the bore exceeds the maximum limit
deposits from bearing shells.
and /or if the rod is fractured, it should be
b. Inspection. Inspect each bearing carefully.
replaced.
Bearings that have a scored, chipped, or worn
(6) On connecting rods that have a piston
surface should be replaced. Typical examples of
pin bushing, check the piston pin to connecting
bearings that should be replaced and the causes
rod bushing clearance. Replace the connecting rod
are shown in figure 6-44. The copper-lead bearing
if the bushing is so worn that it cannot be reamed
base may be visible through the bearing overlay.
or honed for an oversize pin.
This does not mean that the bearing is worn. It is
(7) Check the ID of the connecting rod
not necessary to replace the bearing if the bearing
piston pin bore. Replace the connecting rod if the
clearance is within recommended limits. Check
pin bore is not within specifications. Replace
the clearance of bearings that appear to be
defective connecting rod nuts and bolts.
satisfactory with Plastigage. Fit new bearings
(8) After the connecting rods are assembled
following the recommended procedure in
to the piston, check the rods for bend or twist on a
suit able alignment  fixture.  F o l l o w the in-
structions of the fixture manufacturer. If the
bend and/or twist exceeds specification, the rod
must be straightened or replaced.
Figure 6-44. Typical Bearing Failures.
with a standard bearing to obtain the proper
6-33. Fitting Main and Connecting Rod Bearings
clearance.
a. Set-up.
(2) If fitting a main bearing, position a jack
( 1 ) Clean crankshaft journals. Inspect
.
under counterweight adjoining bearing which is
journals and thrust faces (thrust bearing) for
being checked. Do not place jack under front post
nicks, burrs or bearing pick-up that would cause
of crankshaft. Support crankshaft with jack so its
premature bearing wear. When replacing stan-
weight will not compress Plastigage and provide
dard bearings with new bearings, it is good
an erroneous reading,
practice to fit the bearing to minimum specified
b. Use of Plastigage.
clearance. If the desired clearance cannot be
(1) Place a piece of Plastigage on bearing
obtained with a standard bearing, try one-half of
surface across full width of bearing cap and about
an 0.001 or 0.002 inch undersize in combination
1/4 inch off center (fig. 6-45).

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