Checking The Piston Rings - Yamaha YZF-R25 Service Manual

b. If out of specification, replace the cylinder,
and replace the piston and piston rings as a
set.
c. Measure piston skirt diameter D "a" with the
micrometer.
Diameter
59.962–59.585 mm (2.3607–
2.3459 in)
b
b. 7.0 mm (0.28 in) from the bottom edge of the
piston
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
0.015–0.048 mm (0.0006–0.0019
in)
f. If out of specification, replace the cylinder,
and replace the piston and piston rings as a
set.
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EAS30292

CHECKING THE PISTON RINGS

The following procedure applies to both of the
piston rings.
a
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CYLINDER AND PISTONS
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.
Piston ring
2. Install:
• Piston ring
(into the cylinder)
TIP
Level the piston ring into the cylinder with the
piston crown.
3. Measure:
• Piston ring end gap
Out of specification → Replace the piston
ring.
TIP
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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5-36
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)