Checking The Piston Pin; Installing The Piston And Cylinder - Yamaha YZ250F Owner's Service Manual

CHECKING THE PISTON PIN

EAS1SM5231
1. Check:
• Piston pin
Blue discoloration/grooves  Replace the
piston pin and then check the lubrication
system.
2. Measure:
• Piston pin outside diameter "a"
Out of specification  Replace the piston
pin.
Piston pin outside diameter
15.991–16.000 mm (0.6296–
0.6299 in)
Limit
15.971 mm (0.6288 in)
3. Measure:
• Piston pin bore inside diameter "b"
Out of specification  Replace the piston.
Piston pin bore inside diameter
16.002–16.013 mm (0.6300–
0.6304 in)
Limit
16.043 mm (0.6316 in)
EAS1SM5232
b
CYLINDER AND PISTON

INSTALLING THE PISTON AND CYLINDER

1. Install:
• Oil ring expander "1"
• Lower oil ring rail "2"
• Upper oil ring rail "3"
• Top ring "4"
TIP
Be sure to install the piston ring so that the
manufacturer's marks or numbers face up.
2. Install:
• Piston "1"
• Piston pin "2"
• Piston pin clip "3"
TIP
• Apply the engine oil to the piston pin.
• Install the piston with the F mark "a" on it
pointing to its intake (front) side.
• Before installing the piston pin clip, cover the
crankcase opening with a cloth to prevent the
clip from falling into the crankcase.
• Install the piston pin clips, so that the clip ends
are 3 mm (0.12 in) "c" or more from the cutout
in the piston.
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