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TM 5-4320-305-24
4-13.
REPLACE/REPAIR CRANKCASE ASSEMBLY (Continued)
21
Check main bearing bore.
a.
If a main bearing cap bore is within or just slightly outside tolerance limits or if a new main bearing cap is
being used, loosen bolts (1) alternately and evenly far enough to be able to install main bearings (2). Make
sure matchmarks are correctly alined if new bearings are not being in- stalled. Make sure oil passage is
installed in upper bearing cap. If new caps or bearings are being installed, match-mark them. Tighten and
retighten bolts as in step 20b.
b.
Measure main bearing bore with micrometer (3) at points 1 and 2 and along axes A and B. Bore should
measure 2.8757 to 2.8772 inches (73.042 to 73.081 mm). If measurement is not within these tolerance
limits, main bearing must be replaced.
c.
If measurements were taken with new main bearings and a main bearing cap that was only slightly outside
tolerance limits, the acceptable main bearing tolerance limits may be increased to 2.8749 to 2.878 inches
(73.022 to 73.101 mm). If measurements are still not within these extended tolerance limits, the main bear-
ing caps and crankcase must be replaced.
22
Check radial clearance.
a.
Replacement of main bearings depends on the diameter of the crankshaft center bearing journal. Measure
diameter and determine radial clearance by subtracting journal diameter from bearing bore. Clearance
should be 0.0020 to 0.0043 inch (0.052 to 0.110 mm). Maximum allowable clearance is 0.0118 inch (0.3
mm).
b.
If radial clearance is not within these tolerance limits, recheck main bearings, main bearing cap, and/or
crankshaft. Replace components in that order until clearance is within tolerance limits.
23
Check side clearance.
a.
Measure width of crankshaft center bearing journal. Measure width of main bearing cap at bearing bore.
Determine side clearance by subtracting bearing cap width from bearing journal width. Side clearance
should be 0.0059 to 0.0124 inch (0.150 to 0.314 mm). Maximum allowable clearance is 0.0157 inch (0.4
mm).
b.
If side clearance is not within these tolerance limits, recheck main bearing cap and crankshaft center bearing
journal. Replace in that order until side clearance is within tolerance limits.
4-112
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