Replacement - Mercury MerCruiser MCM 454 Mag MPI Service Manual

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SERVICE MANUAL NUMBER 23

journal is out of round .001 in., interference between the bearing and journal will result in

rapid bearing failure. If the flattened gauging plastic tapers toward the middle or ends, there

is a difference in clearance indicating taper, low spot or other irregularity of the bearing or

journal. Be sure to measure the journal with a micrometer if the flattened gauging plastic

indicates more than .001 in. difference.

6. If the bearing clearance is within specifications, the bearing insert is satisfactory. If the

7. A standard, or .001 in., undersize bearing may produce the proper clearance. If not, it

After selecting new bearing, recheck clearance.

8. Proceed to the next bearing. After all bearings have been checked, rotate the crankshaft

9. Measure crankshaft end play (see "Specifications") by forcing the crankshaft to the

Replacement

NOTE: Main bearings may be replaced with or without removing crankshaft.

90-861326--1 MARCH 1999

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clearance is not within specifications, replace the insert. Always replace both upper and

lower inserts as a unit.

will be necessary to regrind the crankshaft journal for use with the next undersize

to see that there is no excessive drag. When checking No. 1 main bearing, loosen acces-

sory drive belts so as to prevent tapered reading with plastic gauge.

extreme front position. Measure at the front end of the rear main bearing with a feeler

gauge as shown.

Measuring Crankshaft End Play - (Force Crankshaft To Extreme Forward

Main Bearing Inserts

Lower Bearing Insert (Install In Cap)

Upper Bearing Insert (Install In Block)

454 CID (7.4L) / 502 CID (8.2L)

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