3.9
Engine/Cooling/Exhaust
3
Piston Inspection
Check piston for scoring or cracks in piston crown or pin
area. Excessive carbon buildup below the ring lands is an
indication of piston, ring or cylinder wear.
Using only a micrometer, measure the piston outside
d
iameter at a 90° angle to the direction of the piston pin
and at the specified measuring point.
NOTE: A micrometer is the only recommended tool to
ac
curately measure piston diameter.
Subtract this measurement from the minimum cylinder
me
asurement (90° to the pin). If clearance exceeds the
service limit piston/cylinder overhaul may be required.
Piston Ring Installed Gap
Position the ring 20mm from the top of the cylinder using
the piston to push it squarely into place. Measure installed
gap with a feeler gauge at both the top and bottom of the
cylinder.
NOTE: A difference in end gap indicates cylinder
t
aper. The cylinder should be measured for excessive
taper and out-of-round. Replace rings if the installed
end gap exceeds the service limit. Always check
piston ring installed gap after re-boring a cylinder or
when installing new rings.
Piston rings are installed with marking or beveled side up.
Measuring Point
600/800 Pistons: 10-20mm
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