Yamaha YZ125 2009, Owner'S Service Manual

Page: 106 / 234

4-23
CYLINDER HEAD, CYLINDER AND PISTON
CHECKING THE COMBINATION OF PISTON
AND CYLINDER
1. Check:
• Cylinder mark "a"
2. Check:
• Piston mark "a"
3. Combination:
Combine the piston and cylinder by the fol-
lowing chart.
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 clearance:
Standard <Limit>
0.040–0.045 mm
(0.0016–0.0018 in)
0.1 mm (0.004 in)
Cylinder mark "a" Cylinder size
A
54.000–54.002 mm
(2.1260–2.1261 in)
B
54.004–54.006 mm
(2.1261–2.1262 in)
C
54.008–54.010 mm
(2.1263–2.1264 in)
D
54.012–54.014 mm
(2.1265–2.1265 in)
Piston mark "a" (col-
or)
Piston size
A (red)
53.957–53.960 mm
(2.1243–2.1244 in)
B (orange)
53.961–53.964 mm
(2.1244–2.1246 in)
C (green)
53.965–53.968 mm
(2.1246–2.1247 in)
D (purple)
53.969–53.972 mm
(2.1248–2.1249 in)
Cylinder mark Piston mark (color)
A A (red)
B B (orange)
C C (green)
D D (purple)