Engine Service Manual

78
Disassembly/Inspection and Service
KohlerEngines.com 32 690 03 Rev. I
3. When bore is within 0.064 mm (0.0025 in.) of
desired size, remove coarse stones and replace
them with burnishing stones. Continue with
burnishing stones until bore is within 0.013 mm
(0.0005 in.) of desired size and then use fi nish
stones (220-280 grit) and polish bore to its 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, and too steep an angle will result in high
oil consumption.
4. After resizing, 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 3 locations in
cylinder – at top, middle, and bottom. Two
measurements should be taken (perpendicular to
each other) at 3 locations.
Clean Cylinder Bore After Honing
Proper cleaning of cylinder walls following boring and/
or honing is very critical to a successful overhaul.
Machining grit left in cylinder bore can destroy an engine
in less than 1 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
A
A 6 mm (0.2362 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
6 mm (0.2362 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 difference between bore
diameter and piston diameter (step 2 minus step 1).