Yamaha RS90GTZ Service Manual page 293

CONNECTING RODS AND PISTONS
5-68
2nd step:
• Measure piston skirt diameter "P" with the
micrometer.
11.0 mm (0.43 in) from the bottom edge of the
piston.
Piston size (standard) (P):
81.950 ~ 81.965 mm
(3.2264 ~ 3.2270 in)
• If out of specification, replace the piston
and piston rings as a set.
3rd step:
• Calculate the piston-to-cylinder clearance
with the following formula.
Piston-to-cylinder clearance =
Cylinder bore "C" –
Piston skirt diameter "P"
Piston-to-cylinder clearance:
0.035 ~ 0.060 mm
(0.0014 ~ 0.0024 in)
<Limit>: 0.120 mm (0.0047 in)
• If out of specification, replace the crank-
case, and the piston and piston rings as a
set.
3. Measure:
• Piston ring side clearance
Use the thickness gauge
Out of specification → Replace the piston
and piston rings as a set.
TIP
Before measuring the piston ring side clear-
ance, eliminate any carbon deposits from the
piston ring grooves and piston rings.
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)
ENG
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