Yamaha BR250F Service Manual page 18

Inspection
1. Piston pin and bearing inspection.
a. Check the piston pin for signs of wear.
If any wear is evident, replace the pin
and the bearing.
b. Check the pin and bearing for signs of
heat discoloration. If excessive (indenta-
tion on pin, etc.), replace the pin and the
bearing.
c. Check the small-end bearing for exces-
sive wear or damage. Check the rollers
for signs of flat spots. If such wear is
found, replace the pin and the bearing.
d. Apply a light film of oil to the pin and
bearing surfaces. Install them in the
connecting rod small end to inspect for
wear. Check for play. There should be
no noticeable vertical play. If play exists,
check the connecting rod small end for
wear. Replace pin, connecting rod and/
or bearing, as required.
2-7
e. The piston pin should have no noticeable
free play in the piston. If the piston pin
is loose, replace the pin and/or piston.
2. Piston
a. Remove the piston rings.
b. Remove any carbon deposits from piston
crown.
c. Carefully remove any carbon deposits
from the ring grooves.
d. Hernove score marks and lacquer
deposits from the sides of the piston
using 600 -- 800 grit wet sandpaper.
Sand in a crisscross pattern. Do not sand
excessively.