Checking The Piston Rings - Yamaha WR250F 2016 Owner's Service Manual

b. If out of specification, rebore or replace the
cylinder, and replace the piston and the pis-
ton rings as a set.
c. Measure the piston outside diameter "a" at
the measuring point (from piston skirt bot-
tom) "b" with the micrometer.
Diameter
76.955–76.970 mm (3.0297–
3.0303 in)
Measuring point (from piston
skirt bottom)
6.0 mm (0.24 in)
b
d. If out of specification, replace the cylinder,
the piston, and the piston rings as a set.
e. Calculate the piston-to-cylinder clearance
with the following formula.
Piston-to-cylinder clearance =
Cylinder bore - Piston diameter
Piston-to-cylinder clearance
0.030–0.055 mm (0.0012–0.0022
in)
Limit
0.15 mm (0.006 in)
f. If out of specification, replace the cylinder,
the piston, and the piston rings as a set.
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EAS2GB7259
a
CYLINDER AND PISTON

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.
Ring side clearance
0.030–0.065 mm (0.0012–0.0026
in)
Limit
0.120 mm (0.0047 in)
2. Install:
• Piston rings
TIP
Level the piston ring into the cylinder with the
piston.
a. 10 mm (0.39 in)
3. Measure:
• Piston ring end gap
Out of specification  Replace the piston
ring.
TIP
The oil ring expander's end gap cannot be
measured. If the oil ring rail's gap is excessive,
replace all three oil rings.
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