Yamaha YP125R - Checking the Piston Rings

CYLINDER AND PISTON (YP250R)
5-86
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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EAS24430
CHECKING THE PISTON RINGS
1. Measure:
• Piston ring side clearance
Out of specification → Replace the piston
and piston rings as a set.
T
IP
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)
T
IP
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
68.965–68.980 mm (2.7152–
2.7157 in)
• Piston-to-cylinder clearance =
Cylinder bore “C” -
Piston skirt diameter “D”
Piston-to-cylinder clearance
0.020–0.040 mm (0.0008–0.0016
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
0.130 mm (0.0051 in)
2nd ring
Ring side clearance
0.030–0.070 mm (0.0012–
0.0028 in)
Limit
0.130 mm (0.0051 in)
a. 5 mm (0.20 in)