Valve Grinding - Mercury MerCruiser MCM 454 Mag MPI Service Manual

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SERVICE MANUAL NUMBER 23

Regardless of type of equipment, however, it is essential that valve guide bores be free from

carbon or dirt to achieve proper centering of pilot in valve guide, ensuring concentricity.

Valve Grinding

Valves that are pitted must be refaced to the proper angle. Valve stems that show excessive

wear or valves that are warped excessively must be replaced. When a valve head that is

warped excessively is refaced, a knife edge will be ground on part or all of the valve head

due to the amount of metal that must be removed to completely reface. Knife edges lead

to breakage, burning or pre-ignition due to heat localizing on this knife edge. If the edge of

the valve head is less than 1/32 in. (0.8 mm) after grinding, replace the valve.

Several different types of equipment are available for refacing valves. The recommendation

of the manufacturer of the equipment being used should be carefully followed to attain prop-

90-861326--1 MARCH 1999

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Measuring Valve Seat Concentricity

0.372 In. (9.45 mm)

1/32 [.031] In. (0.79 mm) Min.

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

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