Checking The Small End Bearing; Checking The Power Valve; Checking The Power Valve Hole On Cylinder; Assembling The Power Valve - Yamaha YZ125X 2021 Owner's Service Manual

Piston-pin-to-piston-pin-bore
clearance
0.008–0.023 mm (0.0003–0.0009
in)
Limit
0.065 mm (0.0026 in)
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 power valve hole surface "a")
TIP
Do not use a sharp instrument. Avoid scratching
CYLINDER HEAD, CYLINDER AND PISTON
the aluminum.
EAM30551

ASSEMBLING THE POWER VALVE

1. Install:
• Power valve 1 "1"
• Power valve 2 "2"
• Bolt (power valve) "3"
TIP
Install the power valve at cut-away faced "a" for
down side.
2. Install:
• Spring "1"
• Link lever "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 base grease on the oil
seal lip.
5-11
Bolt (power valve)
8 N·m (0.8 kgf·m, 5.9 lb·ft)
a
2
1
3
Power valve link lever bolt
4.0 N·m (0.40 kgf·m, 3.0 lb·ft)
3