Locating Noisy Lifters - Mercury MerCruiser MCM 454 Mag MPI Service Manual

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

Locating Noisy Lifters

Locate a noisy valve lifter by using a piece of garden hose approximately 4 ft (1.2 m) in
length. Place one end of hose near end of each intake and exhaust valve, with other end
of hose to the ear. In this manner, sound is localized, making it easy to determine which lifter
is at fault.
Another method is to place a finger on face of valve spring retainer. If lifter is not functioning
properly, a distinct shock will be felt when valve returns to its seat.
General types of valve lifter noise are as follows:
1. Hard rapping noise - usually caused by plunger becoming tight in bore of lifter body so
that return spring cannot push plunger back up to working position. Probable causes
are:
a. Excessive varnish or carbon deposit, causing abnormal stickiness.
b. Galling or "pickup" between plunger and bore of lifter body, usually caused by an
2. Moderate rapping noise - probable causes are:
a. Excessively high leakdown rate.
b. Leaky check valve seat.
c. Improper adjustment.
3. General noise throughout valve train - this will, in most cases, be a definite indication
of insufficient oil supply or improper adjustment.
4. Intermittent clicking - probable causes are:
a. A microscopic piece of dirt momentarily caught between ball seat and check valve
b. In rare cases, ball itself may be out of round or have a flat spot.
c. Improper adjustment.
In most cases, where noise exists in one or more lifters, all lifter units should be removed,
disassembled, cleaned in solvent, reassembled and reinstalled in engine. If dirt, corrosion,
carbon, etc., is shown to exist in one unit, it more likely exists in all the units; thus it would
only be a matter of time before all lifters caused trouble.
Index
Page 3A-34
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abrasive piece of dirt or metal wedged between plunger and lifter body.
ball.
SERVICE MANUAL NUMBER 23
90-861326--1 MARCH 1999