Checking The Piston Rings - Yamaha YFM50S Service Manual

CYLINDER AND PISTON
EBS00250

CHECKING THE PISTON RINGS

1. Measure:
• piston ring side clearance
Out of specification → Replace the piston
and piston rings as a set.
NOTE:
_
Before measuring the piston ring side clear-
ance, eliminate any carbon deposits from the
piston ring grooves and piston rings.
Piston ring side clearance
Top ring
0.030 ~ 0.065 mm
(0.0012 ~ 0.0026 in)
<Limit>: 0.12 mm (0.0047 in)
2nd ring
0.020 ~ 0.055 mm
(0.0008 ~ 0.0022 in)
<Limit>: 0.12 mm (0.0047 in)
2. Install:
• piston ring
(into the cylinder)
NOTE:
_
Level the piston ring into the cylinder with the
piston crown.
3. Measure:
• piston ring end gap
Out of specification → Replace the piston
ring.
NOTE:
_
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.
Piston ring end gap
Top ring
0.08 ~ 0.20 mm
(0.0031 ~ 0.0079 in)
<Limit>: 0.45 mm (0.0177 in)
2nd ring
0.05 ~ 0.20 mm
(0.0020 ~ 0.0079 in)
<Limit>: 0.55 mm (0.0217 in)
Oil ring
0.20 ~ 0.70 mm
(0.0079 ~ 0.0276 in)
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ENG