Main Bearing Description; Bearing Insert Pairs; Main Bearing-To-Journal Clearance Measurement - Jeep 1987 Wrangler Workshop Manual

CYLINDER BLOCK
ASSEMBLY
If the end play is still not within specifications,
replace the crankshaft.
N O T E : W h e n replacing the thrust bearing, pry
the crankshaft fore and aft to align the f a c e s of
the thrust bearing before the final tightening.
MAIN BEARING DESCRIPTION
T h e main crankshaft bearings are the steel-
backed, micro-babbitt, two-piece precision type.
T h e main bearing c a p s , numbered (front to rear)
from 1 through 7, have an arrow to indicate the
forward position.
T h e upper main bearing inserts are grooved
to provide oil channels. T h e lower inserts a r e
smooth.
E a c h bearing insert pair is selectively fitted to
its respective journal to obtain the specified
operating c l e a r a n c e .
In production, the select fit is obtained by using
various-sized, color-coded bearing insert pairs
a s listed in t h e M A I N B E A R I N G F I T T I N G
C H A R T . T h e bearing color c o d e a p p e a r s on
the edge of the insert.
N O T E : T h e s i z e is not stamped on inserts u s e d
for engine production.
T h e main bearing journal s i z e (diameter) is
identified in production by a color-coded paint
mark on the adjacent c h e e k toward the flanged
(rear) end of the crankshaft, except for the rear
main journal, which is on the crankshaft rear
flange.
When required, the upper and lower bearing
inserts of different s i z e s may be used a s a pair. A
standard s i z e insert is s o m e t i m e s u s e d in
c o m b i n a t i o n with a 0 . 0 2 5 m m ( 0 . 0 0 1 in.)
undersize insert to reduce the c l e a r a n c e by
0.013 mm (0.0005 in.).
Example:
B E A R I N G I N S E R T PAIRS
Insert
Correct Incorrect
Upper Standard
Standard
Lower
0.025 mm (0.001 in.)
undersize
0.051 mm (0.002 in.)
undersize
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C A U T I O N : Never u s e a pair of bearing inserts
with g r e a t e r t h a n a 0 . 0 2 5 m m ( 0 . 0 0 1 in.)
difference in s i z e .
C A U T I O N : W h e n replacing the inserts, the odd
size inserts must be either all on the top (in the
cylinder block) or all on the bottom (in the main
bearing c a p ) .
MAIN BEARING-TO-JOURNAL CLEARANCE
MEASUREMENT
[Using Plastigage With Crankshaft Installed]
A heavier wear pattern is s e e n on the lower
bearing (A) than on the upper bearing ( B ) . A low
a r e a in the lower bearing lining is illustrated at
(C). No w e a r is s h o w n at (D).
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