10.7
Section 10
Inspection and Reconditioning
10
Inspection and Service
A er cleaning, check the fl atness of the cylinder head
and the corresponding top surface of the crankcase,
using a surface plate or piece of glass and feeler
gauge. The maximum allowable out of fl atness is
0.1 mm (0.0039 in.).
Carefully inspect the valve mechanism parts. Inspect
the valve springs and related hardware for excessive
wear or distortion. Check the valves and valve seat
area or inserts for evidence of deep pi ing, cracks, or
distortion. Check clearance of the valve stems in the
guides. See Figure 10-9 for valve details.
Hard starting, or loss of power accompanied by high
fuel consumption may be symptoms of faulty valves.
Although these symptoms could also be a ributed to
worn rings, remove and check the valves fi rst. A er
removal, clean the valve heads, faces, and stems with
a power wire brush. Then, carefully inspect each valve
for defects such as warped head, excessive corrosion,
or worn stem end. Replace valves found to be in bad
condition. A normal valve and valves in bad condition
are shown in the accompanying illustrations.
Normal: Even a er long hours of operation a valve
can be reconditioned and reused if the face and
margin are in good shape. If a valve is worn to where
the margin is less than 1/32 in. do not reuse it. The
valve shown was in operation for almost 1000 hours
under controlled test conditions.
Bad Condition: The valve depicted here should be
replaced. Note the warped head; margin damaged
and too narrow. These conditions could be a ributed
to excessive hours or a combination of poor operating
conditions.
Leakage: A poor grind on face or seat of valve will
allow leakage resulting in a burned valve on one side
only.
Coking: Coking is normal on intake valves and is not
harmful. If the seat is good, the valve could be reused
a er cleaning.
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