Yamaha BR250F Service Manual page 20

4. Cylinder
a. Remove all carbon deposits from the
cylinder and from the ports. Carburetor
cleaner will help lift carbon from the
cyl inder head. Thoroughly wash the
cylinder in solvent, and blow it dry with
compressed air.
b. Inspect the cylinder walls for scratches.
If vertical scratches are evident, the
cylinder should be rebored or replaced.
c. Measure the cylinder wall wear at the
places shown in the illustration; use a
cyl inder bore gauge. If wear is excessive,
compression pressure will decrease; re-
bore or replace the cylinder.
----------
Standard Wear limit
Cylinder bore
70.00 ......, 70.02 mm
70.05 mm
(2.756 -2.757 in)
(2.776 in)
Cylinder taper
0.05mm
(0.002 in)
Cylinder out-of-
0.01 mm
round
-
(0.004 in)
"~-'-
,,~ ~~
.......
------_...-....,.......,.,..
Boring
If the cylinder requires boring, follow the
standard boring procedures but use an offset
bit as shown below. This bit is standard
equipment with some boring bars. Be sure
that the depth adjustment is precisely set so
the combustion chamber is not damaged.
Honing
Whenever honing the cylinder on the BR250,
use a hone with a bumper device so the com-
bustion chamber will not be carelessly
damaged. Otherwise follow standard honing
procedures. Yamaha recommends the use of
an Ammco Hone. This kit includes all the
necessary piecesto properly hone the cylinder
on the BR250.
Ammco Hone Kit: TLU-03950-00-00