2008 YAMAHA YZ450F check engine light

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Page 54 of 188

YAMAHA YZ450F 2008  Owners Manual 3-8
ENGINE
CHECKING THE ENGINE OIL 
LEVEL
1. Stand the machine on a level sur-
face.
• When checking the oil level make 
sure that the machine is upright.
• Place the machine on a suitable 
stand.

Page 55 of 188

YAMAHA YZ450F 2008  Owners Manual 3-9
ENGINE
Replacement steps:
a. Remove the oil filter element cov-
er "1" and oil filter element "2".
b. Check the O-rings "3", if cracked 
or damaged, replace them with a 
new one.
c. Install the oi

Page 68 of 188

YAMAHA YZ450F 2008  Owners Manual 3-22
ELECTRICAL
ELECTRICAL
CHECKING THE SPARK PLUG
1. Remove:
• Spark plug
2. Inspect:
• Electrode "1"
Wear/damage
→Replace.
• Insulator color "2"
Normal condition is a medium to 
light tan co

Page 85 of 188

YAMAHA YZ450F 2008  Owners Manual 4-17
CAMSHAFTS
Measurement steps:
a. Install the camshaft onto the cylin-
der head.
b. Position a strip of Plastigauge
® 
"1" onto the camshaft.
c. Install the clip, dowel pins and 
camshaft caps.

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 124 of 188

YAMAHA YZ450F 2008  Owners Manual 4-56
CRANKCASE AND CRANKSHAFT
DISASSEMBLING THE 
CRANKCASE
1. Separate:
• Right crankcase
• Left crankcase
Separation steps:
a. Remove the crankcase bolts, 
hose guide and clutch cable hold-
er.
L

Page 126 of 188

YAMAHA YZ450F 2008  Owners Manual 4-58
CRANKCASE AND CRANKSHAFT
5. Install:
• Dowel pin "1"
• O-ring "2" 
• Right crankcase
To left crankcase.
• Apply the lithium soap base grease 
on the O-ring.
• Fit the right crankcase on

Page 178 of 188

YAMAHA YZ450F 2008  Owners Manual 7-1
ENGINE
TUNING
ENGINE
CARBURETOR SETTING
• The air/fuel mixture will vary de-
pending on atmospheric conditions. 
Therefore, it is necessary to take 
into consideration the air pressure, 
ambient