Service Manual

57
Disassembly/Inspection and Service
66 690 01 Rev. C KohlerEngines.com
Remove Flywheel End Oil Seals
Remove fl ywheel end crankshaft and camshaft oil seals
from crankcase.
Crankcase
Inspection and Service
NOTE: If bore is beyond wear limit, a new miniblock or
short block will be required.
Check all gasket surfaces to make sure they are free of
gasket fragments. Gasket surfaces must also be free of
deep scratches or nicks.
Inspect main bearing (if equipped) for wear or damage.
Replace crankcase using a mini-block or short block if
required.
Check cylinder bore for scoring. In severe cases,
unburned fuel can cause scuffi ng and scoring of cylinder
wall. It washes necessary lubricating oils off piston and
cylinder wall. As raw fuel seeps down cylinder wall,
piston rings make metal to metal contact with wall.
Scoring of cylinder wall can also be caused by localized
hot spots resulting from a cooling system problem or
from inadequate or contaminated lubrication.
If cylinder bore is badly scored, excessively worn,
tapered, or out-of-round, resizing is necessary. Use
an inside micrometer to determine amount of wear,
then select nearest suitable oversize of either 0.08 mm
(0.003 in.), 0.25 mm (0.010 in.), or 0.50 mm (0.020 in.).
Resizing to one of these oversizes will allow usage of
available oversize piston and ring assemblies. Initially,
resize using a boring bar, then use following procedures
for honing cylinder.
Honing
Detail
A
A 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
crossbore. 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 so
that 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.
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 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 three locations in
cylinder-at top, middle, and bottom. Two
measurements should be taken (perpendicular to
each other) at each three 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 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 that is 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.