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Figure 3-84. Upper and lower main bearing shells, bearing caps, and rear main bearing thrust washers.
TM-10-3930-243-34 Truck Lift Fork Diesel Engine Pneumatic Tired Wheels Rough Terrain 10 000 lb. Capacity 24 Inch Load Center Manual
Figure 3-86. Rear main bearing thrust washer and mounting.
Minimum thickness of a worn standard main bearing
shell is 0.123 inch and, if any of the shells are thinner
than this dimension, all shells must be discarded and
replaced with new shells. A new bearing shell has a
thickness of 0.1245 to 0.1250 inch.
(4) In addition to this thickness measurement,
the clearance between main  bearings and
crankshaft journals should be checked. This
clearance may be determined with the crankshaft in
place by means of a soft plastic measuring strip
which is squeezed between journal and bearing, or
w i t h the crankshaft removed by measuring the
o u t s i d e diameter of the crankshaft main bearing
j o u r n a l s and the inside diameter of the main
b e a r i n g shells when installed in place with the
proper torque of 120-130 foot-pounds on the main
b e a r i n g cap bolts. If the clearance between any
c r a n k s h a f t main bearing journal and its bearing
shells exceeds 0.006 inch, all bearings shells must
be discarded and replaced with new shells. This
clearance is 0.0013 to 0.0042 inch.
( 5 ) W h e n m a i n b e a r i n g r e p l a c e m e n t  is
necessary, it is very important that the crankshaft
j o u r n a l s be thoroughly inspected before new
r e p l a c e m e n t bearings are installed. Very often,
after prolonged engine operation, a ridge is formed
on the circumference of the crankshaft journals in
line with the journal oil holes. This ridge must not
exceed 0.0002 inch and, if it is not moved before
n e w bearings are installed, then during engine
o p e r a t i o n , localized high unit pressures in the
center area of the bearing shell will cause pitting of
Figure 3-85. Removing rear main bearing upper shell
the bearing surface. Also, damaged bearings may
(crankshaft in place).
cause bending fatigue and resultant cracks in the
c. Inspection.
(1) After removal, clean the bearing shells and
O n e main bearing shell alone should
inspect them for scoring, pitting, flaking, chipping,
n o t be replaced. If one bearing shell
cracking, loss of babbitt or signs of overheating. If
requires replacement, a new upper and
any of these defects are present, the bearings must
l o w e r shell should be installed.
be discarded. However, the babbitt plated bearings
d. Installation (crankshaft in place).
m a y develop minute cracks or small isolated
cavities on the bearing surface during engine
operation. These are characteristics of and are not
Make sure all parts are clean. Apply clean engine oil
to all crankshaft journals and install main bearing
detrimental to this type of bearing. The bearings
shells by reversing the sequence of operations given
s h o u l d not be replaced for these minor surface
for removal.
imperfections since functioning of the bearings is in
no way impaired and they will give many additional
M a i n bearing  s h e l l s s h o u l d n o t b e
hours of trouble-free operation. The lower bearing
r e p l a c e d separately. If bearing shell
shells, which carry the load, will normally show
requires replacement, a new upper and
signs of distress before the upper shells do.
lower shell should be installed. If a new
(2) Inspect the back of the bearing shells for
crankshaft is used all new bearing
bright spots which indicate they have been moving
s h e l l s should be installed.
in the caps or cylinder block. If such spots are
(1) When installing the upper main bearing
present, discard the bearing shells.
shells with crankshaft in place, start the end of the
(3) The thickness of the bearing shells should
shell having no tang around the crankshaft journal,
be measured at point C, 90 from parting line.

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