Checking The Piston Rings; Checking The Piston Pin - Yamaha WR250R Service Manual

d. If out of specification, replace the cylinder,
piston and piston rings as a set.
e. Calculate the piston-to-cylinder clearance
with the following formula.
Piston-to-cylinder clearance =
Cylinder bore "D" -
Piston skirt diameter "P"
Piston-to-cylinder clearance
0.010–0.035 mm (0.0004–0.0014
in)
Limit
0.10 mm (0.0039 in)
f. If out of specification, replace the cylinder,
piston and piston rings as a set.
LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL
EAS24430

CHECKING THE PISTON RINGS

1. Measure:
Piston ring side clearance
G
Out of specification → Replace the piston
and piston rings as a set.
NOTE:
Before measuring the piston ring side clearance,
eliminate any carbon deposits from the piston
ring grooves and piston rings.
Piston ring side clearance
Top ring side clearance (installed)
0.030–0.065 mm (0.0012–0.0026
in)
Limit
0.115 mm (0.0045 in)
Second ring side clearance (in-
stalled)
0.020–0.055 mm (0.0008–0.0022
in)
Limit
0.115 mm (0.0045 in)
CYLINDER AND PISTON
2. Install:
Piston ring
G
(into the cylinder)
NOTE:
Level the piston ring into the cylinder with the
piston crown.
a. 40 mm (1.57 in)
3. Measure:
Piston ring end gap
G
Out of specification → Replace the piston
ring.
NOTE:
The oil ring expander spacer's end gap cannot
be measured. If the oil ring rail's gap is exces-
sive, replace all three piston rings.
Piston ring end gap
Top ring
End gap (installed)
0.15–0.25 mm (0.0059–0.0098 in)
Limit
0.50 mm (0.020 in)
2nd ring
End gap (installed)
0.30–0.45 mm (0.0118–0.0177 in)
Limit
0.80 mm (0.031 in)
Oil ring
End gap (installed)
0.10–0.40 mm (0.0039–0.0157 in)
EAS24440

CHECKING THE PISTON PIN

1. Check:
Piston pin
G
Blue discoloration/grooves → Replace the
piston pin and then check the lubrication sys-
tem.
2. Measure:
Piston pin outside diameter "a"
G
Out of specification → Replace the piston pin.
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