Checking The Small End Bearing; Checking The Power Valve; Checking The Power Valve Hole On Cylinder; Assembling The Power Valve - Yamaha YZ250 2022 Owner's Service Manual

4. Calculate:
• Piston-pin-to-piston-pin-bore clearance
Out of specification  Replace the piston pin
and piston as a set.
Piston-pin-to-piston-pin-bore clearance =
Piston pin bore inside diameter "b" -
Piston pin outside diameter "a"
Piston-pin-to-piston-pin-bore
clearance
0.004–0.020 mm (0.0002–0.0008
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 1 "2"
• Power valve link lever "3"
• Pulley "4"
• Power valve shaft "5"
• Link rod "6"
• Washer "7"
Wear/damage  Replace.
• Spring 1, 2 "8"
Broken  Replace.
CYLINDER HEAD, CYLINDER AND PISTON
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
the aluminum.
EAM30551

ASSEMBLING THE POWER VALVE

1. Install:
• Power valve 1 "1"
• Power valve holder 2 "2"
• Bolt (power valve holder 2) "3"
TIP
• Install the power valve 1 with its gouge "a" fac-
ing upside.
• Apply the molybdenum disulfide oil on the pow-
er valve 1.
5-10
Power valve holder 2
6 N·m (0.6 kgf·m, 4.4 lb·ft)
LOCTITE®