Mercury MerCruiser MCM 454 Mag MPI Service Manual page 273

SERVICE MANUAL NUMBER 23
5. Slip outer surface of a new top and second compression ring into respective piston ring
6. Proper clearance of piston ring in its piston ring groove is very important to provide
PISTON PINS
1. Piston pin clearance is designed to maintain adequate clearance under all engine
2. Inspect piston pin bores and piston pins for wear. Piston pin bores and piston pins must
Index
90-861326--1 MARCH 1999
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groove and roll ring entirely around the groove to make sure that ring is free as shown.
If binding occurs at any point, determine cause. If caused by ring groove, remove by
dressing with a fine cut file. If binding is caused by a distorted ring, recheck with another
ring.
proper ring action and reduce wear. Therefore, when fitting new rings, clearances
between ring and groove surfaces should be measured. See "Specifications."
operating conditions. Because of this, piston and piston pin are a matched set and not
serviced separately.
be free of varnish and scuffing when measured. Measure piston pin with a micrometer
and piston pin bore with a dial bore gauge or inside micrometer. If clearance is in excess
of the .001 in. (0.025 mm) wear limit, replace piston and piston pin assembly.
454 CID (7.4L) / 502 CID (8.2L)
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