Valve Guide Bore Repair - Mercury MerCruiser MCM 454 Mag MPI Service Manual

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SERVICE MANUAL NUMBER 23

IMPORTANT: Excessive valve stem to bore clearance will cause excessive oil con-

sumption and possible valve breakage. Insufficient clearance will result in noisy and

sticky valves.

5. Measure valve stem clearance as follows:

Valve Guide Bore Repair

IMPORTANT: Be sure to measure valve stem diameter of both the intake and exhaust

valve, as valve stem diameter may or may not be the same for both valves.

If .015 in. oversize valves are required, ream valve guide bores for oversize valves, as fol-

1. Measure valve stem diameter of old valve being replaced and select proper size valve

2. Ream valve guide bores, as shown.

3. Remove the sharp corner created by reamer at top of valve guide.

90-861326--1 MARCH 1999

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a. Attach a dial indicator to cylinder head, positioning it against the valve stem and

close to the valve guide.

b. Holding valve head off seat about 1/16 in. (2 mm), move valve stem back and forth

in direction shown. Compare stem clearance with specifications.

Dial Indicator

c. If clearance exceeds specifications, it will be necessary to ream valve guides for

oversized valves, as outlined under "Valve Guide Bore Repair."

guide reamer from chart below.

Standard Valve Stem Diameter

Reamer Required For .015 In. Oversize Valve

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

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