Yamaha YP125R, Service Manual

Page: 272 / 498

CYLINDER AND PISTON (YP125R)
5-27
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 “a” with the
micrometer.
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.
f. If out of specification, rebore or replace the
cylinder, and replace the piston and piston
rings as a set.
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EAS37P1081
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 clearance,
eliminate any carbon deposits from the piston
ring grooves and piston rings.
2. Install:
• Piston ring
(into the cylinder)
TIP
Level the piston ring into the cylinder with the
piston crown.
b. 5 mm (0.20 in) from the bottom edge of the
piston
Piston
Diameter D
51.962–51.985 mm (2.0457–
2.0466 in)
• Piston-to-cylinder clearance =
Cylinder bore “C” -
Piston skirt diameter “D”
Piston-to-cylinder clearance
0.015–0.048 mm (0.0006–0.0019
in)
Limit
0.15 mm (0.0059 in)
Piston ring
Top ring
Ring side clearance
0.040–0.080 mm (0.0016–
0.0031 in)
Limit
0.120 mm (0.0047 in)
2nd ring
Ring side clearance
0.030–0.070 mm (0.0012–
0.0028 in)
Limit
0.120 mm (0.0047 in)
a. 10 mm (0.39 in)