Yamaha MBK MW125 2014, Service Manual

Page: 234 / 380

CYLINDER AND PISTON
5-31
3. Measure:
• Piston ring end gap
Out of specification
→
Replace the piston
ring.
TIP
The oil ring expander spacer end gap cannot be
measured. If the oil ring rail gap is excessive, re-
place all three piston rings.
EAS30293
CHECKING THE PISTON PIN
1. Check:
• Piston pin
Blue discoloration/grooves
→
Replace the
piston pin, and then check the lubrication sys-
tem.
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 piston.
4. Calculate:
• Piston-pin-to-piston-pin-bore clearance
Out of specification
→
Replace the piston pin
and piston as a set.
EAS30290
CHECKING THE TIMING CHAIN GUIDE
(EXHAUST SIDE)
1. Check:
• Timing chain guide (exhaust side)
Damage/wear
→
Replace.
EAS30294
INSTALLING THE PISTON AND CYLINDER
1. Install:
• Lower oil ring rail “1”
• Oil ring expander “2”
• Upper oil ring rail “3”
• 2nd ring “4”
• Top ring “5”
TIP
Be sure to install the piston rings so that the
manufacturer marks face up.
Piston ring
Top ring
End gap (installed)
0.07–0.17 mm (0.0028–0.0067
in)
Limit
0.42 mm (0.0165 in)
2nd ring
End gap (installed)
0.35–0.50 mm (0.0138–0.0197
in)
Limit
0.85 mm (0.0335 in)
Oil ring
End gap (installed)
0.20–0.70 mm (0.0079–0.0276
in)
Piston pin outside diameter
13.995–14.000 mm (0.5510–
0.5512 in)
Limit
13.975 mm (0.5502 in)
Piston pin bore inside diameter
14.002–14.013 mm (0.5513–
0.5517 in)
Limit
14.043 mm (0.5529 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
0.002–0.018 mm (0.0001–0.0007
in)