Checking The Power Valve; Checking The Power Valve Hole On Cylinder - Yamaha YZ125 2009 Owner's Service Manual

Piston clearance:
Standard
0.040–0.045 mm
(0.0016–0.0018 in)
CHECKING THE COMBINATION OF PISTON
AND CYLINDER
1. Check:
• Cylinder mark "a"
Cylinder mark "a"
A
B
C
D
2. Check:
• Piston mark "a"
Piston mark "a" (col-
or)
A (red)
B (orange)
C (green)
D (purple)
CYLINDER HEAD, CYLINDER AND PISTON
<Limit>
0.1 mm (0.004 in)
Cylinder size
54.000–54.002 mm
(2.1260–2.1261 in)
54.004–54.006 mm
(2.1261–2.1262 in)
54.008–54.010 mm
(2.1263–2.1264 in)
54.012–54.014 mm
(2.1265–2.1265 in)
Piston size
53.957–53.960 mm
(2.1243–2.1244 in)
53.961–53.964 mm
(2.1244–2.1246 in)
53.965–53.968 mm
(2.1246–2.1247 in)
53.969–53.972 mm
(2.1248–2.1249 in)
4-23
3. Combination:
Combine the piston and cylinder by the fol-
lowing chart.
Cylinder mark
A
B
C
D
When you purchase a cylinder, you cannot des-
ignate its size. Choose the piston that matches
the above chart.

CHECKING THE POWER VALVE

1. Inspect:
• Power valve 1,2 "1"
Wear/Damage → Replace.
Carbon deposits → Remove.
• Valve holder "2"
• Link lever "3"
• Valve shaft "4"
• Collar "5"
Wear/Damage → Replace.
• Spring "6"
Broken → Replace.
CHECKING THE POWER VALVE HOLE ON
CYLINDER
1. Remove:
• Carbon deposits
From power valve hole surface "a".
Piston mark (color)
A (red)
B (orange)
C (green)
D (purple)