10.5
Section 10
Inspection and Reconditioning
10
Figure 10-7. Cylinder Bore Crosshatch After
Honing.
4. A er resizing, check the bore for roundness,
taper, and size. Use an inside micrometer,
telescoping gauge, or bore gauge to take
measurements. The measurements should be
taken at three locations in the cylinder – at the
top, middle, and bo om. Two measurements
should be taken (perpendicular to each other) at
each of the three locations.
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 le in the cylinder bore can destroy
an engine in less than one hour of operation a er a
rebuild.
The fi nal cleaning operation should always be a
thorough 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,
discard the dirty water and start again with more
hot water 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 o en overlooked, and if the clearances are
not within specifi cations, engine failure will usually
result.
NOTE: Do not use a feeler gauge to measure piston-
to-bore clearance–it will yield inaccurate
measurements. Always use a micrometer.
Use the following procedure to accurately measure
the piston-to-bore clearance:
1. Use a micrometer and measure the diameter of
the piston above the bo om of the piston skirt
and perpendicular to the piston pin. See Figure
10-8.
Figure 10-8. Measuring Piston Diameter.
2. Use an inside micrometer, telescoping gauge,
or bore gauge and measure the cylinder bore.
Take the measurement approximately 7.0 mm
(0.2760 in.) below the top of the bore and
perpendicular to the piston pin.
3. Piston-to-bore clearance is the diff erence between
the bore diameter and the piston diameter (Step 2
minus Step 1).
Flywheel
Inspection
Inspect the fl ywheel for cracks, and the fl ywheel
keyway for damage. Replace fl ywheel if it is cracked.
Replace the fl ywheel, the cranksha , and the key if the
fl ywheel key is sheared or the keyway is damaged.
Measure Above the Bottom
of Piston Skirt at Right
Angles to Piston Pin
CH270 CH395 CH440
21.8-22.2 mm
(0.8583-0.8740 in.)
17.8-18.2 mm
(0.7008-0.7165 in.)
29.8-30.2 mm
(1.1732-1.1890 in.)
Refer to Chart
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