Yamaha WR250F Manuel D'atelier page 360

CYLINDER AND PISTON
Piston ring
1. Measure:
Ring side clearance
G
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.
Top ring
2nd ring
2. Position:
Piston ring
G
(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
G
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.
Top ring
2nd ring
Oil ring
4 - 46
ENG
Side clearance:
Standard
0.030 ~ 0.065 mm
(0.0012 ~ 0.0026 in)
0.020 ~ 0.055 mm
(0.0008 ~ 0.0022 in)
End gap:
Standard
0.15 ~ 0.25 mm
(0.006 ~ 0.010 in)
0.30 ~ 0.45 mm
(0.012 ~ 0.018 in)
0.10 ~ 0.40 mm
(0.004 ~ 0.016 in)
<Limit>
0.12 mm
(0.005 in)
0.12 mm
(0.005 in)
<Limit>
0.50 mm
(0.020 in)
0.80 mm
(0.031 in)
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