Yamaha YZ125(P)/LC, Owner'S Service Manual

Page: 254 / 564

4-21
ENG
CYLINDER HEAD, CYLINDER AND PISTON
EC474301
Piston
1. Remove:
9
Carbon deposits
From the piston crown
a
and ring groove
b
.
2. Inspect:
9
Piston wall
Score marks
→
Repair or replace.
3. Measure:
9
Piston skirt diameter
Use micrometer
1
.
Measure the specific distance
a
from the
bottom edge.
Out of specification
→
Replace.
2. Inspect:
9
Cylinder inner surface
Score marks
→
Repair or replace.
Use #400~600 grit wet sandpaper.
c C
Do not rebore the cylinder.
3. Measure:
9
Cylinder bore “C”
Use cylinder gauge
1
.
Out of limit
→
Replace.
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.
17.5 mm 53.957~53.972 mm
(0.69 in) (2.1243~2.1249 in)
Standard Wear limit
Cylinder 54.000~54.014mm 54.1 mm
bore “C” (2.1260~2.1265 in) (2.130 in)
Taper “T” —
0.05 mm
(0.0020 in)
C=Maximum Aa~Cb
T=(Maximum Aa, or Ab) —
(Maximum Ba, or Bb)
Distance
a a
Piston dia.
5NY-9-30-4B 5/23/01 8:48 PM Page 8