2008 YAMAHA YZ450F Owners Manual

Page 89 of 188

YAMAHA YZ450F 2008  Owners Manual 4-21
CYLINDER HEAD

Page 90 of 188

YAMAHA YZ450F 2008  Owners Manual 4-22
VALVES AND VALVE SPRINGS
VALVES AND VALVE SPRINGS
REMOVING THE VALVES AND VALVE SPRINGS
Order Part name Qty Remarks
Cylinder head Refer to "CYLINDER HEAD" section.
1 Valve lifter 5 Refer to remo

Page 91 of 188

YAMAHA YZ450F 2008  Owners Manual 4-23
VALVES AND VALVE SPRINGS
REMOVING THE VALVE LIFTER 
AND VALVE COTTER
1. Remove:
• Valve lifter "1"
•  Pad "2"
Identify each lifter "1" and pad "2" po-
sition very carefully so that they can

Page 92 of 188

YAMAHA YZ450F 2008  Owners Manual 4-24
VALVES AND VALVE SPRINGS
4. Measure:
• Margin thickness "a"
Out of specification
→Replace.
5. Measure:
• Runout (valve stem)
Out of specification
→Replace.
• When installing a new valve

Page 93 of 188

YAMAHA YZ450F 2008  Owners Manual 4-25
VALVES AND VALVE SPRINGS
CHECKING THE VALVE SPRINGS
1. Measure:
• Valve spring free length "a"
Out of specification
→Replace.
2. Measure:
• Compressed spring force "a"
Out of specification

Page 94 of 188

YAMAHA YZ450F 2008  Owners Manual 4-26
CYLINDER AND PISTON
CYLINDER AND PISTON
REMOVING THE CYLINDER AND PISTON
Order Part name Qty Remarks
Cylinder head  Refer to "CYLINDER HEAD" section.
1 Bolt (cylinder) 1
2 Cylinder 1
3 Gasket 1

Page 95 of 188

YAMAHA YZ450F 2008  Owners Manual 4-27
CYLINDER AND PISTON
REMOVING THE PISTON AND 
PISTON RING
1. Remove:
• Piston pin clip "1"
• Piston pin "2"
• Piston "3"
• Put identification marks on each 
piston head for reference durin

Page 96 of 188

YAMAHA YZ450F 2008  Owners Manual 4-28
CYLINDER AND PISTON
3. Measure:
• Ring end gap
Out of specification
→Replace.
You cannot measure the end gap on 
the expander spacer of the oil control 
ring. If the oil control ring rails sh