Yamaha YZ250 2022, Owner'S Service Manual

Page: 172 / 274

CYLINDER HEAD, CYLINDER AND PISTON
5-10
4. Calculate:
• Piston-pin-to-piston-pin-bore clearance
Out of specification

Replace the piston pin
and piston as a set.
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.
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.
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)
Power valve holder 2
6 N·m (0.6 kgf·m, 4.4 lb·ft)
LOCTITE®
T
R
.
.