Checking The Piston; Checking The Piston Pin And Small End Bearing - Yamaha YZ125 2009 Owner's Service Manual

CHECKING THE PISTON

1. Eliminate:
• Carbon deposits
From the piston crown "a" and ring groove
"b".
2. Inspect:
• Piston wall
Score marks → Repair or replace.
3. Measure:
• Piston skirt diameter
Use micrometer "1".
Measure the specific distance "a" from the
bottom edge.
Out of specification → Replace.
Distance "a"
17.5 mm
(0.69 in)
CYLINDER HEAD, CYLINDER AND PISTON
Piston dia.
53.957–53.972 mm
(2.1243–2.1249 in)
4-21
CHECKING THE PISTON PIN AND SMALL
END BEARING
1. Inspect:
• Piston pin
• Small end bearing
Signs of heat discoloration → Replace.
2. Measure:
• Piston pin outside diameter
Use micrometer "1".
Out of limit → Replace.
Piston pin outside diameter:
Standard
14.995–15.000 mm
(0.5904–0.5906 in)
<Limit>
14.975 mm (0.5896
in)