15
PISTON ASSEMBLY
NOTE: Oversized pistons are available allowing the
cylinder to be bored oversized.
NOTE: Whenever a piston, rings, or pins 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.
NOTE: If seizure marks or scuffing is detected, the
piston must be replaced.
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.
2. Remove each ring by working it toward the dome of
the piston while rotating it out of the groove.
NOTE: Note the location of each ring for proper
installation. When installing new rings, install as a
complete set only.
Cleaning/Inspecting Piston Rings
NOTE: Make a ring-groove cleaning tool by taking
an old piston ring and snapping it into two pieces;
then grind the end of the old ring to a 45° angle and to
a sharp edge.
Using a ring-groove cleaning 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 piston ring in the wear portion of the cyl-
inder. Use the piston to position each ring squarely in
the cylinder.
NOTE: When measuring a piston ring, it should be
placed into the area of the cylinder where wear is least
(the area is about 0.12" from the upper or lower edge
of the cylinder).
2. Using a feeler gauge, measure each piston-ring end
gap. Acceptable ring end gap must be within 0.008-
0.016" (1st and 2nd rings) or within 0.0079-0.0157"
(oil ring).
IO083
IO090
Piston Ring/Groove Clearance
1. Using a thickness gauge, measure the side clearances
of the 1st and 2nd rings.
2. If the measurements are not within 0.0016- 0.0030"
(1st ring) or 0.0008-0.0024" (2nd ring), replace both
piston and piston rings.
Measuring Piston Skirt/Cylinder
Clearance
1. Measure the cylinder front to back in six places using
a cylinder bore gauge. The amount of wear is the dif-
ference between the largest and smallest readings. If
the determined wear exceeds the limit indicated, bore
to the next oversize by using a boring machine or
replace the cylinder.
GEN-0032
2. Measure the corresponding piston diameter at a point
10 mm above the piston skirt at a right angle to the
piston-pin bore. Piston diameter must be at least
2.205".
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.
