Yamaha YZ125 2022, Owner'S Service Manual, Page: 172 / 278

CYLINDER HEAD, CYLINDER AND PISTON
5-12
EAM30550
CHECKING THE SMALL END BEARING
1. Check:
• Small end bearing
Signs of heat discoloration

Replace.
EAM30553
CHECKING THE POWER VALVE
1. Check:
•
Power valve 1, 2 “1”
Wear/damage

Replace.
Carbon deposits

Remove.
• Power valve holder “2”
•
Link lever “3”
• Valve shaft “4”
•
Collar “5”
Wear/damage

Replace.
•
Spring “6”
Broken

Replace.
EAM30552
CHECKING THE POWER VALVE HOLE ON
CYLINDER
1. Remove:
• Carbon deposits
(from the power valve hole surface “a”)
TIP
Do not use a sharp instrument. Avoid scratching
the aluminum.
EAM30551
ASSEMBLING THE POWER VALVE
1. Install:
• Power valve 2 “1”
•
Power valve 1 “2”
• Bolt (power valve) “3”
TIP
Install the power valve at cut-away faced “a” for
down side.
2. Install:
• Link lever “1”
•
Spring “2”
• Collar “3”
•
Valve shaft “4”
• Power valve holder “5”
•
Power valve link lever bolt “6”
TIP
• Install the spring to the link lever, and then to
the cylinder.
• Install the spring with its stopper portion “a” fac-
ing inward.
• Apply the lithium-soap-based grease on the oil
seal lip.
Piston-pin-to-piston-pin-bore
clearance
0.008–0.023 mm (0.0003–0.0009
in)
Limit
0.065 mm (0.0026 in)
1
2
3
4
5
6
5
6
Bolt (power valve)
8 N·m (0.8 kgf·m, 5.9 lb·ft)
Power valve link lever bolt
4.0 N·m (0.40 kgf·m, 3.0 lb·ft)
a a
T
R
.
.
a
1
2
3
T
R
.
.