Yamaha YZ450FY 2009 Owner's Service Manual page 80

ADJUSTING THE VALVE CLEARANCE
• This section is intended for those who have
basic knowledge and skill concerning the ser-
vicing of Yamaha motorcycles (e.g., Yamaha
dealers, service engineers, etc.) Those who
have little knowledge and skill concerning ser-
vicing are requested not to undertake inspec-
tion, adjustment, disassembly, or reassembly
only by reference to this manual. It may lead
to servicing trouble and mechanical damage.
• The valve clearance should be adjusted when
the engine is cool to the touch.
• The piston must be at Top Dead Center
(T.D.C.) on compression stroke to check or
adjust the valve clearance.
1. Remove:
• Seat
• Fuel tank
Refer to "SEAT, FUEL TANK AND SIDE
COVERS" section in the CHAPTER 4.
2. Remove:
• Spark plug
• Engine upper bracket
• Hot starter plunger
Refer to "CARBURETOR" section in the
CHAPTER 4.
• Cylinder head cover
Refer to "CAMSHAFTS" section in the
CHAPTER 4.
3. Remove:
• Timing mark accessing screw "1"
• Crankshaft end accessing screw "2"
• O-ring
4. Check:
• Valve clearance
Out of specification → Adjust.
Valve clearance (cold):
Intake valve:
0.10–0.15 mm (0.0039–0.0059 in)
Exhaust valve:
0.20–0.25 mm (0.0079–0.0098 in)
Checking steps:
a. Turn the crankshaft counterclockwise with a
wrench.
b. Align the T.D.C. mark "a" on the rotor with
the align mark "b" on the crankcase cover
when piston is at T.D.C. on compression
stroke.
In order to be sure that the piston is at Top
Dead Center, the punch mark "c" on the ex-
haust camshaft and the punch mark "d" on the
intake camshaft must align with the cylinder
head surface, as shown in the illustration.
3-15
ENGINE