The bearing shells do not form a true
circle
when
not
installed.
When
installed,
the bearing shells have a
squeeze fit in the main bearing bore and
must be tight when the bearing cap is
drawn down. This crush assures a tight
uniform
contact between the bearing
shell a n d b e a r i n g s e a t .
Bearing shells
that do not have sufficient crush will not
have uniform contact, as shown by shiny
spots
on
the
back,
and
must
be
replaced.
If the clearance between any
crankshaft journal and its bearing shells
exceeds 0.0060", all of the bearing shells
must be discarded and replaced. This
clearance is 0.0014" to 0.0044" with new
parts.
Before installing new replacement bear-
ings, it is very important to thoroughly
inspect t h e c r a n k s h a f t j o u r n a l s . V e r y
often, after prolonged engine operation,
a ridge is formed on the crankshaft jour-
nals in line with the journal oil holes. If
Figure 11B-91. Main Bearing
Measurements
t h i s r i d g e i s not removed before new
bearings are installed, then, during en-
gine
operation,
localized
unit
line, as shown in Figure 11B-91 on page
high
pressures in the center area of the bear-
11B-59 and Figure 11B-92 on page
11B-59.
Tool J 4757, placed between the
ing shell will cause pitting of the bearing
surface.
bearing shell and a micrometer, will give
Also, damaged bearings may
The bearing
cause b e n d i n g f a t i g u e a n d r e s u l t a n t
an accurate measurement.
cracks in the crankshaft.
shell thickness will be total thickness of
the steel ball in the tool and the bearing
Do not replace one main bearing shell
shell, less the diameter of the ball. This
alone.
If one bearing shell requires re-
is the only practical method for measur-
unless a
placement, install all new upper and low-
ing the bearing thickness,
er bearing shells.
A l s o , if a new or
special micrometer is available for this
The minimum thickness of a
reground crankshaft is to be used, in-
purpose.
stall all new bearing shells.
worn standard main bearing shell is
0.1530" and, if any of the bearing shells
Bearing shells are available in 0.010"
are thinner than this dimension, replace
all of the bearing shells. The thickness
0.020" and 0.030" undersize for service
with reground crankshafts.
To deter-
of new and undersize bearing shells are
mine the size bearings required, refer to
given in Figure 11B-91.
thickness
addition
to
the
In
measurement, c h e c k t h e c l e a r a n c e b e -
tween the main bearings and the crank-
This clearance may be
shaft journals.
determined with the crankshaft in place
by means of a soft plastic measuring
strip which is squeezed between the
journal and the bearing (refer to "Shop
Note - Troubleshooting" on page
11B-122). With the crankshaft removed
measure t h e o u t s i d e d i a m e t e r o f t h e
crankshaft main bearing journals and the
i n s i d e diameter of the main bearing shells
when installed in place with the proper
torque on the bearing cap bolts. When
installed, the bearing shells are 0.001"
F i g u r e 11B-92. Measuring Thickness
larger in diameter at the parting line
of Bearing Shell
than 90 from the parting line.
E n g i n e (Less Major Assemblies)
