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3
PISTON ASSEMBLY
NOTE: Whenever a piston, rings, or pin are out of
tolerance, they must be replaced.
Cleaning/Inspecting Piston
1. Using a non-metallic carbon removal tool, remove
any carbon buildup from the dome of the piston.
2. Inspect the piston for cracks in the piston pin,
dome, and skirt areas.
3. Inspect the piston for seizure marks or scuffing.
Repair with #400 grit wet-or-dry sandpaper and
water or honing oil.
NOTE: If scuffing or seizure marks are too deep
to correct with the sandpaper, replace the piston.
4. Inspect the perimeter of each piston for signs of
excessive “blowby.” Excessive “blowby” indicates
worn piston rings or an out-of-round cylinder.
Removing Piston Rings
1. Starting with the top ring, slide one end of the ring
out of the ring-groove.
CC400D
2. Remove each ring by working it toward the dome
of the piston while rotating it out of the groove.
NOTE: If the existing rings will not be replaced
with new ones, note the location of each ring for
proper installation. When installing new rings,
install as a complete set only.
Cleaning/Inspecting Piston Rings
1. Take an old piston ring and snap it into two pieces;
then grind the end of the old ring to a 45° angle
and to a sharp edge.
2. Using the sharpened ring as a tool, clean carbon
from the ring-grooves. Be sure to position the ring
with its tapered side up.
Measuring Piston-Ring End Gap
(Installed)
1. Place each compression ring in the wear portion of
the cylinder. Use the piston to position each ring
squarely in the cylinder.
2. Using a feeler gauge, measure each piston-ring
end gap. Acceptable ring end gap must be within
specifications.
CC280D
Measuring Piston Pin (Outside
Diameter) and Piston-Pin Bore
1. Measure the piston pin outside diameter at each
end and in the center. If measurement is not within
specifications, the piston pin must be replaced.
ATV-1070
2. Insert an inside dial indicator into the piston-pin
bore. The diameter must not exceed specifications.
Take two measurements to ensure accuracy.
CAUTION
Improper cleaning of the ring-grooves by the use of
the wrong type of ring-groove cleaner will result in
severe damage to the piston.
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