Yamaha RS90K Manuel D'atelier page 532

CRANKCASE
"C" = maximum of D
"T" = maximum of D
or D
6
"R" = maximum of D
D D or D
2 4 6
• If out of specification, replace the cylinder, and
the piston and piston rings as a set.
2nd step:
• Measure piston skirt diameter "P" with the
micrometer.
a 5.0 mm (0.20 in) from the bottom edge of the piston.
Piston size (standard) (P):
78.935 ~ 78.950 mm
(3.1077 ~ 3.1083 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:
0.050 ~ 0.075 mm
(0.0020 ~ 0.0030 in)
<Limit>: 0.120 mm (0.0047 in)
• If out of specification, replace the cylinder, and
the piston and piston rings as a set.
3. Measure:
• Piston ring side clearance
Use the thickness gauge 1.
Out of specification → Replace the piston and
piston rings as a set.
NOTE:
Eliminate the carbon deposits from the piston ring
grooves and rings before measuring the side clear-
ance.
5-57
ENG
~ D
1 6
or D – maximum of D
1 2
D or D – maximum of
1 3 5
5