Yamaha WR250F Manuel D'atelier page 354

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CYLINDER AND PISTON
4 - 44
Cylinder bore "C"
(3.0315 ~ 3.0319 in)
Taper limit "T"
Out of round "R"
"C" = Maximum D
"T" = (Maximum D or D
1
– (Maximum D
"R" = (Maximum D , D
1 3
– (Minimum D
If out of specification, replace the cylinder,
and replace the piston and piston rings as
set.
2nd step:
Measure the piston skirt diameter "P" with
a micrometer.
a 8 mm (0.31 in) from the piston bottom edge
76.955 ~ 76.970 mm
Standard
(3.0297 ~ 3.0303 in)
If out of specification, replace the piston
and piston rings as a set.
3rd step:
Calculate the piston-to-cylinder clearance
with following formula:
Piston-to-cylinder clearance =
Cylinder bore "C" –
Piston skirt diameter "P"
Piston-to-cylinder clearance:
0.040 ~ 0.065 mm
(0.0016 ~ 0.0026 in)
<Limit>: 0.1 mm (0.004 in)
If out of specification, replace the cylinder,
and replace the piston and piston rings as
set.
ENG
77.00 ~ 77.01 mm
0.05 mm (0.002 in)
0.05 mm (0.002 in)
)
2
or D )
5 6
or D )
5
, D or D )
2 4 6
Piston size "P"