Checking The Piston Rings - Yamaha XG250 Service Manual

a
b
b. 11 mm (1 in) from the bottom edge of the piston
Piston size diameter "D"
Standard
73.960–73.975 mm (2.9118–2.9124
in)
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
0.025–0.050 mm (0.0010–0.0020
in)
Limit
0.15 mm (0.0059 in)
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.
NOTE:
Before measuring the piston ring side clearance,
eliminate any carbon deposits from the piston
ring grooves and piston rings.
CYLINDER AND PISTON
Piston ring
Top ring
Ring side clearance
0.030–0.065 mm (0.0012–0.0026
in)
Limit
0.100 mm (0.0039 in)
2nd ring
Ring side clearance
0.020–0.055 mm (0.0008–0.0022
in)
Limit
0.100 mm (0.0039 in)
2. Install:
Piston ring
●
(into the cylinder)
NOTE:
Level the piston ring into the cylinder with the
piston crown.
a. 40 mm (1.476 in)
3. Measure:
Piston ring end gap
●
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.
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