Yamaha YFM250RX 2008 Service Manual page 149

CYLINDER AND PISTON
a. Measure cylinder bore "C" with the cylinder
bore gauge.
NOTE: NOTE:
Measure cylinder bore "C" by taking side-to-
side and front-to-back measurements of the
cylinder. Then, find the average of the mea-
surements.
Bore "C"
74.000 ~ 74.016 mm
(2.9134 ~ 2.9140 in)
Wear limit
74.100 mm (2.9173 in)
"C" = maximum of D1 ~ D6
b. If out of specification, rebore or replace the
cylinder, and replace the piston and piston
rings as a set.
c. Measure piston skirt diameter D
micrometer.
5 mm (0.20 in) from the bottom edge of the pis-
ton
Piston size diameter "D"
Standard
73.983 ~ 73.998 mm
(2.9127 ~ 2.9133 in)
d. If out of specification, replace the piston
and piston rings as a set.
e. Calculate the piston-to-cylinder clearance
with the following formula.
Piston-to-cylinder clearance =
Cylinder bore "C" -
Piston skirt diameter "D"
4-33
ENG
with the