Yamaha YZ85(T) Owner's Service Manual page 236

CYLINDER HEAD, CYLINDER AND PISTON
3. Measure:
Cylinder bore "C"
G
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.
5PA40490
Cylinder
bore "C"
Taper "T"
C = Maximum Aa ~ Cb
T = (Maximum Aa, or Ab) –
(Maximum Ba, or Bb)
5PA40500
Piston
1. Eliminate:
Carbon deposits
G
From the piston crown a and ring groove
b.
2. Inspect:
Piston wall
G
Score marks → Replace.
3. Measure:
5PA40510
Piston skirt diameter
G
Use micrometer 1.
Measure the specific distance a from the
bottom edge.
Out of specification → Replace.
5PA40520
Piston pin and small end bearing
1. Inspect:
Piston pin
G
Small end bearing
G
Signs of heat discoloration → Replace.
5PA40530
4 - 19
ENG
Standard
47.500 ~ 47.514 mm
(1.8701 ~ 1.8706 in)
–
Piston dia.:
47.457 ~ 47.472 mm
(1.8684 ~ 1.8690 in)
Distance a:
20 mm (0.79 in)
Wear limit
47.6 mm
(1.8740 in)
0.05 mm
(0.0020 in)