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SECTION 10
INSPECTION AND RECONDITIONING
Figure 10-3.
Measuring Cylinder Bore.
Clean Cylinder Bore After Honing
Proper cleaning of the cylinder walls following boring
and/or honing is very critical to a successful overhaul.
Machining grit left in the cylinder bore can destroy an
engine in less than one hour of operation after a
rebuild.
The final cleaning operation should always be a thor-
ough scrubbing with a brush and hot, soapy water.
Use a strong detergent that is capable of breaking
down the machining oil while maintaining a good level
of suds. If the suds break down during cleaning, dis-
card the dirty water and start again with more hot wa-
ter and detergent. Following the scrubbing, rinse the
Cylinder with very hot, clear water, dry it completely,
and apply a light coating of engine oil to prevent
rusting.
Measuring Piston-to-Bore Clearance
Before installing the piston into the cylinder bore, it is
necessary that the clearance be accurately checked.
This step is often overlooked, and if the clearances
are not within specifications, generally engine failure
will result.
NOTE:
Do not use a feeler gauge to measure piston-
to-bore clearance——it will yield inaccurate
measurements--Use a micrometer.
The following procedures should be used to accurate-
ly measure the piston-to-bore clearance:
1. Use a micrometer and measure the diameter of
the piston, 1/2" above bottom of piston skirt, per-
pendicular to the piston pin (see Figure 10-4).
Figure 10-4. Measuring Piston Diameter
(Style "D" Piston)
2. Use an inside micrometer, telescoping gauge, or
bore gauge and measure the cylinder bore. Take
the measurement approximately 2- 1/2" below the
top of the bore and perpendicular to the piston
pin.
3. Piston-to-bore clearance is the difference be-
tween the bore and the piston diameter
(step 2 minus step 1).
VALVES
Inspection and Service
Carefully inspect valve mechanism parts. Inspect
valve springs and related hardware for excesslve wear
or distortion. Valve spring free height should be ap-
proximately 1.68" (1-11/16"). Check valves and
valve seat area or inserts for evidence of deep pitting,
cracks, or distortion. Check clearance of valve stems
in guides. See Figure 10-5 for valve details and spec-
ifications for 45° angle or 10-5A for the new 30° ex-
haust valve. See page 10.4.
Hard starting, or loss of power accompanied by high
fuel consumption may be symptoms of faulty valves.
Although these symptoms could also be attributed to
worn rings, remove and check valves first. After re-
moval, clean valve head, face, and stem with power
wire brush and then carefully inspect for defects such
as warped valve head, excessive corrosion, or wom
Stem end. Replace valves found to be in bad condi-
tion. A normal valve and valves in bad conditlon are
shown in the accompanying illustrations.
10.3
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