Yamaha RAPTOR YFM125RA, Service Manual, Page: 192 / 300

CYLINDER AND PISTON
5-29
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.
EAS24440
CHECKING THE PISTON PIN
1. Check:
• Piston pin
Blue discoloration/grooves
→
Replace
the piston pin and then check the lubrica-
tion system.
2. Measure:
• Piston pin outside diameter “a”
Out of specification
→
Replace the piston
pin.
3. Measure:
• Piston pin bore diameter “b”
Out of specification
→
Replace the pis-
ton.
4. Calculate:
• Piston-pin-to-piston-pin-bore clearance
Out of specification
→
Replace the piston
pin and piston as a set.
Piston ring
Top ring
End gap (installed)
0.15–0.30 mm (0.006–0.012 in)
Limit
0.40 mm (0.0157 in)
2nd ring
End gap (installed)
0.30–0.45 mm (0.012–0.018 in)
Limit
0.55 mm (0.0217 in)
Oil ring
End gap (installed)
0.20–0.70 mm (0.008–0.028 in)
a. 40 mm (1.57 in)
Piston pin outside diameter
14.991–15.000 mm (0.5902–
0.5906 in)
Limit
14.971 mm (0.5894 in)
Piston pin bore inside diameter
15.002–15.013 mm (0.5906–
0.5911 in)
Limit
15.043 mm (0.5922 in)
• Piston-pin-to-piston-pin-bore clearance =
Piston pin bore diameter “b” -
Piston pin outside diameter “a”
Piston-pin-to-piston-pin-bore
clearance
0.002–0.022 mm (0.0001–
0.0009 in)
Limit
0.072 mm (0.0028 in)