Yamaha Motor YZ250 N/LC 2001 Manuel D'atelier Du Proprietaire page 252

CYLINDER HEAD, CYLINDER AND PISTON
EC474200
Cylinder
1. Remove:
9Carbon deposits
Use a rounded scraper 1.
NOTE:
Do not use a sharp instrument. Avoid scratching
the aluminum.
2. Inspect:
9Cylinder inner surface
Score marks
Use #400~600 grit wet sandpaper.
cC
Do not rebore the cylinder.
3. Measure:
9Cylinder bore "C"
Use cylinder gauge 1.
Out of limit
NOTE:
Measure the cylinder bore "C" in parallel (A, B,
C) to and at right angles to the crankshaft (a, b).
Then, find the average of the measurements.
Cylinder 66.400~66.414mm
bore "C" (2.6142~2.6147 in)
Taper
"T"
C=Maximum Aa~Cb
T=(Maximum Aa, or Ab) —
(Maximum Ba, or Bb)
EC474320
Piston
1. Remove:
9Carbon deposits
From the piston crown a and ring groove
b.
2. Inspect:
9Piston wall
Score marks
4-21
ENG
Repair or replace.
Replace.
Standard Wear limit
66.5 mm
(2.618 in)
0.05 mm
—
(0.0020 in)
Repair or replace.