Yamaha YZ250N Owner's Service Manual page 254

CYLINDER HEAD, CYLINDER AND PISTON
3. Measure:
9Piston skirt diameter
Use micrometer 1.
Measure the specific distance b from the
stepped surface a on inside of the piston.
Out of specification
Distance
17.5 mm
(0.69 in)
EC474402
Piston pin and small end bearing
1. Inspect:
9Piston pin
9Small end bearing
Signs of heat discoloration
2. Measure:
9Piston pin outside diameter
Use micrometer 1.
Out of limit
Piston pin outside diameter:
Standard
17.995~18.000 mm
(0.7085~0.7087 in)
3. Check:
9Free play (when the piston pin 1 is in
place in the piston 2)
There should be no noticeable for the play.
Free play exists
and/or piston.
4. Install:
9Small end bearing
9Piston pin
Into the small end of connecting rod.
4-22
ENG
Replace.
b b
Piston dia.
66.352~66.367 mm
(2.6120~2.6129 in)
Replace.
Replace.
<Limit>
17.975 mm
(0.7077 in)
Replace piston pin