Inspection; Specifications - MerCruiser GM4 Service Manual

5. Thoroughly clean valve guides with valve guide
cleaner (J-8101).
a - Valve Guide Cleaner (J-8101)

Inspection

1. Inspect cylinder head for cracks in exhaust ports,
water jackets, and combustion chambers (espe-
cially around spark plug holes and valve seats).
Replace heads if any cracks are found.
2. Inspect cylinder head gasket surface for burrs,
nicks, or erosion or other damage. Also, check
flatness of cylinder head gasket surface, using a
machinist's straight edge and feeler gauges as
shown. Refer to "Specifications."
b
a - Straight Edge
b - Feeler Gauge
c - Take Measurements Diagonally Across Head
(Both Ways) and Straight Down Center Head
Index
3A - 18 - ENGINES
a
74286
a
72885
IMPORTANT: Cylinder head-to-block gasket sur-
face should be resurfaced if warped more than
specified. When head resurfacing is required,
cylinder head-to-intake manifold gasket surface
on head must be milled to provide proper align-
ment between intake manifold and head.
3. Inspect valves for burned heads, cracked faces or
damaged stems.
IMPORTANT: Excessive valve stem to bore clear-
ance will cause excessive oil consumption and
possible valve breakage. Insufficient clearance
will result in noisy and sticky valves.
4. Measure valve stem clearance as follows:
a. Attach a dial indicator to cylinder head, posi-
tioning 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 direc-
tion shown. Compare stem clearance with

specifications.

c. If clearance exceeds specifications, it will be
necessary to ream valve guides for oversized
valves, as outlined under "Valve Guide Bore
Repair."
a - Valve Stem
b - Dial Indicator
c - Valve Guide
b
c
a
72336
90-816462 2-695