Yamaha TZ250M1 Owner's Service Manual page 120

CYLINDER HEAD, CYLINDER AND PISTON
3. Inspect:
• Travel distance for cylinder
3,000 km (1,800 miles) or more≥ Replace.
EC474313
Piston
1. Inspect:
• Piston crown
Damage and crack due to detonation≥Replace.
• Piston pin hole
Crack≥ Replace.
• Contact with cylinder
Excessive scuffing, score a ≥ Use
#240~320 grit wet sandpaper in a criss-
cross manner b.
• Heat discoloration≥ Replace.
2. Inspect:
• Travel distance for piston
500 km (300 miles) or more≥ Replace.
3. Check:
• Piston ring free movement
Mechanical stick ≥ Repair.
Install the piston ring 1 to the piston, and
check for free movement.
Repairing steps:
• Remove the piston ring.
• Chamfer the piston ring groove at its edge
a where the piston ring tends to stick,
using a triangle oil stone 2 with the engine
mixing oil.
NOTE:
• Set the triangle oil stone to the piston ring
groove to form an angle of 45°. Do the
chamfering with force applied to this edge.
• Chamfer until the piston ring moves
smoothly.
C C CAUTION:
Do not over-chamfer.
4-22
ENG