TM 5-3810-300-24&P-3
1.3.4
Inspection
Bearing failures may result from deterioration (acid
formation) or contamination of the oil or loss of oil. An
analysis of the lubricating oil may be required to
determine if corrosive acid and sulphur are present
which cause acid etching, flaking and pitting. Bearing
seizure may be due to low oil or no oil. Check oil filter
elements and replace them if necessary. Also check the
oil by-pass valve to make sure it is operating freely.
After removal, clean the bearings and inspect them for
scoring, pitting, flaking, etching, loss of babbitt or signs of
overheating (Fig. 5). The lower bearing shells, which
carry the load, will normally show signs of distress before
the upper bearing shells.
However, babbitt plated
Fig. 3. Removing Upper Main Bearing Shell
bearings may develop minute cracks or small isolated
(Except Rear Main)
cavities on the bearing surface during engine operation.
These are characteristics of and are not detrimental to
2. Remove the oil pump and the oil inlet and outlet
this type of bearing. They should not be replaced for
pipe assemblies.
these minor surface imperfections since function of the
NOTE: If shims are used between the
bearings is in no way impaired and they will give many
oil pump and the main bearing caps,
additional hours of trouble-free operation.
save the shims so that they may be
reinstalled in exactly the same location.
Inspect the backs of the bearing shells for bright spots
which indicate they have been moving in the bearing
3. Remove one main bearing cap at a time (Fig. 2)
caps or bearing supports. If such spots are present,
and inspect the bearing shells as outlined under
discard the bearing shells.
Inspection. Reinstall each bearing shell and cap
before removing another bearing cap:
Measure the thickness of the bearing shells at point "C",
90 from the parting line, as shown in Figs. 6 and 7. Tool
a. To remove all except the rear main
J 4757, placed between the bearing shell and a
bearing shell, insert a 1/4" x 1" bolt with a
1/2" diameter and 1/16" thick head (made
from a standard bolt) into the crankshaft
journal oil hole. Then revolve the shaft to
the right (clockwise) and roll the bearing
shell out of position as shown in Fig. 3.
The bolt head must not extend beyond the
outside diameter of the bearing shell.
b. Remove the rear main bearing upper shell
by tapping on the edge of the bearing with
a small curved rod, revolving the
crankshaft at the same time to roll the
bearing shell out as shown in Fig. 4.
c. The lower halves of the crankshaft thrust
washers will be removed along with the
rear main bearing cap. The upper halves
of the washers can be removed for
inspection by pushing on ends of washers
Fig. 4. Removing Upper Rear Main Bearing Shell
with a small rod, forcing them around and
out of the main bearing support.
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