75
Disassembly/Inspection and Service
22 690 01 Rev. --
KohlerEngines.com
Honing
Detail
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23°-33° Crosshatch
While most commercially available cylinder hones can
be used with either portable drills or drill presses, use
of a low speed drill press is preferred as it facilitates
more accurate alignment of bore in relation to crankshaft
counter bore. Honing is best accomplished at a drill
speed of about 250 RPM and 60 strokes per minute.
After installing coarse stones in hone, proceed as
follows:
1. Lower hone into bore and, after centering, adjust it
so stones are in contact with cylinder wall. Use of a
commercial cutting-cooling agent is recommended.
2. With lower edge of each stone positioned even with
lowest edge of bore, start drill and honing process.
Move hone up and down while resizing to prevent
formation of cutting ridges. Check size frequently.
Make sure bore is cool when measuring.
3. When bore is within 0.064 mm (0.0025 in.) of
desired size, remove coarse stones and replace with
burnishing stones. Continue with burnishing stones
until within 0.013 mm (0.0005 in.) of desired size and
then use fi nish stones (220-280 grit) and polish to
fi nal size. A crosshatch should be observed if honing
is done correctly. Crosshatch should intersect at
approximately 23°-33° off horizontal. Too fl at an
angle could cause rings to skip and wear
excessively, too steep an angle will result in high oil
consumption.
4. After honing, check bore for roundness, taper, and
size. Use an inside micrometer, telescoping gauge,
or bore gauge to take measurements. These
measurements should be taken at three locations in
cylinder – at top, middle, and bottom. Two
measurements should be taken (perpendicular to
each other) at 3 diff erent locations.
Clean Cylinder Bore after Honing
Proper cleaning of cylinder walls following honing is
critical. Grit left in cylinder bore can destroy an engine in
less than one hour of operation after a rebuild.
Final cleaning operation should always be a thorough
scrubbing with a brush and hot, soapy water. Use a
strong detergent capable of breaking down machining
oil while maintaining a good level of suds. If suds break
down during cleaning, discard dirty water and start again
with more hot water and detergent. Following scrubbing,
rinse 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
Piston Detail
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7.5 mm (0.2953 in.)
NOTE: Do not use a feeler gauge to measure piston-to-
bore clearance; it will yield inaccurate
measurements. Always use a micrometer.
Before installing piston into cylinder bore, it is necessary
that clearance be accurately checked. This step is
often overlooked, and if clearances are not within
specifi cations, engine failure will usually result.
Use following procedure to accurately measure piston-
to-bore clearance:
1. Use a micrometer and measure diameter of piston
7.5 mm (0.2953 in.) above bottom of piston skirt and
perpendicular to piston pin.
2. Use an inside micrometer, telescoping gauge, or
bore gauge and measure cylinder bore.
Measurement approximately 63.5 mm (2.5 in.) below
top of bore and perpendicular to piston pin.
3. Piston-to-bore clearance is diff erence between bore
diameter and piston diameter (step 2 minus step 1).
