Checking The Piston Rings - Yamaha RAPTOR YFM125RA Service Manual

a. 40 mm (1.57 in) from the top of the cylinder
b. If out of specification, rebore or replace the
cylinder, and replace the piston and piston
rings as a set.
c. Measure piston skirt diameter "D" with the
micrometer.
Piston
Diameter D
53.997–54.029 mm (2.1259–
2.1271 in)
a. 4.5 mm (0.18 in) from the bottom edge of
the piston
d. If out of specification, replace the piston
and piston rings as a set.
e. Calculate the piston-to-cylinder clearance
with the following formula.
• Piston-to-cylinder clearance =
Cylinder bore "C" - Piston skirt diameter "D"
Piston-to-cylinder clearance
0.019–0.035
0.0014 in)
Limit
0.15 mm (0.006 in)
mm (0.0007–
5-28
CYLINDER AND PISTON
f. If out of specification, rebore or replace the
cylinder, and replace the piston and piston
rings as a set.
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EAS24430

CHECKING THE PISTON RINGS

1. Measure:
• Piston ring side clearance
Out of specification → Replace the piston
and piston rings as a set.
TIP
Before measuring the piston ring side clear-
ance, eliminate any carbon deposits from the
piston ring grooves and piston rings.
Piston ring
Top ring
Ring side clearance
0.035–0.070
0.0028 in)
Limit
0.120 mm (0.0047 in)
2nd ring
Ring side clearance
0.020–0.060
0.0024 in)
Limit
0.120 mm (0.0047 in)
2. Install:
• Piston rings
(into the cylinder)
TIP
Level the piston ring into the cylinder with the
piston crown.
3. Measure:
• Piston ring end gap
Out of specification → Replace the piston
ring.
mm (0.0014–
mm (0.0008–