Yamaha YZ250F(R) Owner's Service Manual page 149

CYLINDER AND PISTON
Piston ring
1. Measure:
Ring side clearance
●
Use a feeler gauge 1.
Out of specification → Replace the pis-
ton and rings as a set.
NOTE:
Clean carbon from the piston ring grooves and
rings before measuring the side clearance.
Side clearance:
0.030 ~ 0.065 mm
Top ring
(0.0012 ~ 0.0026 in)
0.020 ~ 0.055 mm
2nd ring
(0.0008 ~ 0.0022 in)
2. Position:
Piston ring
●
(in cylinder)
NOTE:
Insert a ring into the cylinder and push it
approximately 10 mm (0.39 in) into the cylin-
der. Push the ring with the piston crown so that
the ring will be at a right angle to the cylinder
bore.
a 10 mm (0.39 in)
3. Measure:
Ring end gap
●
Out of specification → Replace.
NOTE:
You cannot measure the end gap on the
expander spacer of the oil control ring. If the oil
control ring rails show excessive gap, replace
all three rings.
End gap:
Top ring
(0.006 ~ 0.010 in)
2nd ring
(0.012 ~ 0.018 in)
Oil ring
(0.004 ~ 0.016 in)
4 - 45
ENG
Standard <Limit>
0.12 mm
(0.005 in)
0.12 mm
(0.005 in)
Standard <Limit>
0.15 ~ 0.25 mm 0.50 mm
(0.020 in)
0.30 ~ 0.45 mm 0.80 mm
(0.031 in)
0.10 ~ 0.40 mm
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