Valve Grinding; Reassembly - Mercury 305 CID Service Manual

Several different types of equipment are available for
reseating valve seats. Equipment manufacturer's
recommendations should be followed carefully to at-
tain proper results.
a
b c
Typical "3 Angle" Valve Seat
a - Top Angle (30 )
b - Seat Angle (46 )
c - Bottom Angle (60 )
d - Seat Width
Intake 1/32-1/16 [.031-.063] In. (0.8-1.5 mm)
Exhaust 1/16-3/32 [.063-.094] In. (1.6-2.3 mm)
Regardless of type of equipment, however, it is es-
sential that valve guide bores be free from carbon or
dirt to achieve proper centering of pilot in valve guide,
ensuring concentricity.
Measuring Valve Seat Concentricity
Index
3A-38 - ENGINES

Valve Grinding

Valves that are pitted must be refaced to the proper
angle. Valve stems which show excessive wear, or
valves that are warped excessively, must be re-
placed. When a valve head which is warped exces-
sively is refaced, a knife edge will be ground on part
d
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 grind-
ing, replace the valve.
Several different types of equipment are available for
refacing valves. The recommendation of the man-
ufacturer of the equipment being used should be
50668
carefully followed to attain proper results.

Reassembly

1. Lubricate valve guides and valve stems with en-
72338
2. Install each valve in the port from which it was re-
3. Install valve guide seal (intake valve only) over
4. Set valve spring (with damper installed) and
EXHAUST
a
b
Exhaust
a - .372 In. (9.45 mm)
b - 1/32 [.031] In. (0.79 mm) Min.
Intake
a - .341 In. (8.16 mm)
b - 1/32 [.031] In. (0.79 mm) Min.
gine oil.
moved or to which it was fitted.
valve stem and push down until seated against
head.
shield in place.
INTAKE
a
b
50695
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