Connecting Rod Bearings; Inspection And Replacement - Mercury MerCruiser MCM 454 Mag MPI Service Manual

SERVICE MANUAL NUMBER 23

Connecting Rod Bearings

Connecting rod bearings are of the precision insert type and do not use shims for adjust-
ment. DO NOT FILE RODS OR ROD CAPS. If clearances are found to be excessive, a new
bearing will be required. Service bearings are available in standard size and .001 in. and
.002 in. undersize for use with new and used standard size crankshafts, and in .010 in. and
.020 in. undersize for use with reconditioned crankshafts.

Inspection and Replacement

IMPORTANT: Before you remove the connecting rod cap, mark the side of the rod and
cap with the cylinder number to assure matched reassembly of rod and cap.
1. With oil pan and oil pump removed, mark the side of the rod and cap with the cylinder
2. Inspect the bearing for evidence of wear and damage. Do not reinstall a worn or
3. Wipe both upper and lower bearing shells and crank pin clean of oil.
4. Measure the crankpin for out-of-round or taper with a micrometer. If not within specifica-
5. If within specifications, measure new or used bearing clearances with gauging plastic
Index
90-861326--1 MARCH 1999
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number and remove the connecting rod cap and bearing.
damaged bearing.
tions, replace or recondition the crankshaft. If within specifications and a new bearing
is to be installed, measure the maximum diameter of the crankpin to determine new
bearing size required.
or its equivalent. If a bearing is being fitted to an out-of-round crankpin, be sure to fit to
the maximum diameter of the crankpin. If the bearing is fitted to the minimum diameter,
and the crankpin is out of round .001 in., interference between the bearing and crankpin
will result in rapid bearing failure.
a. Place a piece of gauging plastic, the length of the bearing (parallel to the crankshaft),
on the crankpin or bearing surface as shown. Position the gauging plastic in the
middle of the bearing shell. (Bearings are eccentric and false readings could occur
if placed elsewhere.)
a - Gauging Plastic
b. Install the bearing in the connecting rod and cap.
c. Install the bearing cap and evenly torque nuts. Refer to "Specifications."
d. Remove the bearing cap and using the scale on the gauging plastic envelope, mea-
sure the gauging plastic width at the widest point as shown.
a
454 CID (7.4L) / 502 CID (8.2L)
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