Yamaha RS90K Service Manual page 260

CRANKCASE
Piston rings side clearance:
Top ring:
0.030 ~ 0.070 mm
(0.0012 ~ 0.0028 in)
2nd ring:
0.020 ~ 0.060 mm
(0.0008 ~ 0.0024 in)
4. Install:
• Piston ring
(into the cylinder)
NOTE:
Level the piston ring in the cylinder with the piston
crown.
a 5.0 mm (0.20 in)
5. Measure:
• Piston ring end gap
Out of specification → Replace the piston
rings as a set.
NOTE:
The oil ring expander spacer's end gap cannot be
measured. If the oil ring rail's gap is excessive,
replace all three piston rings.
Piston ring end gap:
Top ring:
0.35 ~ 0.45 mm (0.014 ~ 0.018 in)
2nd ring:
0.75 ~ 0.85 mm (0.030 ~ 0.033 in)
Oil ring:
0.20 ~ 0.60 mm (0.008 ~ 0.024 in)
6. Inspect:
• Piston pin
Blue discoloration/grooves → Replace the
piston pin and then check the lubrication sys-
tem.
7. Measure:
• Piston pin outside diameter
Out of specification → Replace the piston pin.
Piston pin outside diameter:
18.991 ~ 19.000 mm
(0.7477 ~ 0.7480 in)
5-58
ENG