2003 YAMAHA YZ450F CLEARANCE

3 - 18
INSP
ADJIDLE SPEED ADJUSTMENT/
VALVE CLEARANCE ADJUSTMENT
EC35M021
IDLE SPEED ADJUSTMENT
1. Start the engine and thoroughly warm it
up.
2. Adjust:
Idle speed
Adjustment steps:
Adjust the pilot screw.
Refer to “PILOT SCREW ADJUSTMENT”
section.
Turn the throttle stop screw 1 until the
engine runs at the lowest possible speed.
To increase idle speed →
Turn the throttle stop screw 1 in a.
To decrease idle speed →
Turn the throttle stop screw 1 out b.
Engine idling speed:
1,900 ~ 2,100 r/min
VALVE CLEARANCE ADJUSTMENT
NOTE:
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:
Carburetor
Refer to “CARBURETOR” section in
the CHAPTER 4.
Spark plug cap
Engine stay (upper)
Cylinder head cover
Refer to “CAMSHAFTS” section in the
CHAPTER 4.
3. Remove:
Timing plug 1
Straight plug 2
O-ring

3 - 19
INSP
ADJ
VALVE CLEARANCE ADJUSTMENT
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:
Turn the crankshaft counterclockwise with
a wrench.
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.
NOTE:
In order to be sure that the piston is at Top
Dead Center, the punch mark c on the
exhaust camshaft and the punch mark d on
the intake camshaft must align with the cyl-
inder head surface, as shown in the illustra-
tion.
Measure the valve clearance e using a
feeler gauge 1.
NOTE:
Record the measured reading if the clear-
ance is incorrect.

3 - 20
INSP
ADJ
VALVE CLEARANCE ADJUSTMENT
5. Adjust:
Valve clearance
Adjustment steps:
Loosen the timing chain tensioner cap
bolt.
Remove the timing chain tensioner and
camshaft caps.
NOTE:
Remove the camshaft cap bolts in a criss-
cross pattern from the outside working
inwards.
Remove the camshaft (exhaust 1 and
intake 2).
NOTE:
Attach a wire 3 to the timing chain to pre-
vent it from falling into the crankcase.
Remove the valve lifters 3 and the pads 4.
NOTE:
Place a rag in the timing chain space to
prevent pads from falling into the crank-
case.
Identity each valve lifter and pad position
very carefully so that they can be rein-
stalled in their original place.
Select the proper pad using the pad
selecting table.
Pad rangePad Availability:
25 increments
No. 120
~
No. 2401.20 mm
~
2.40 mmPads are available in
0.05 mm increments
NOTE:
The thickness a of each pad is indicated in
hundreths of millimeters on the pad upper
surface.
1
2
3

3 - 21
INSP
ADJ
VALVE CLEARANCE ADJUSTMENT
Round off the last digit of the installed pad
number to the nearest increment.
Last digit of pad
numberRounded value
0, 1 or 2 0
4, 5 or 6 5
8 or 9 10
EXAMPLE:
Installed pad number = 148
Rounded off value = 150
NOTE:
Pads can only be selected in 0.05 mm incre-
ments.
Locate the rounded-off value and the mea-
sured valve clearance in the chart “PAD
SELECTION TABLE”. The field where
these two coordinates intersect shows the
new pad number to use.
NOTE:
Use the new pad number only as a guide
when verifying the valve clearance adjust-
ment.
Install the new pads 5 and the valve lift-
ers 6.
NOTE:
Apply the engine oil on the valve lifters.
Apply the molybdenum disulfide oil on the
valve stem ends.
Valve lifter must turn smoothly when
rotated with a finger.
Be careful to reinstall valve lifters and
pads in their original place.
Install the camshafts (exhaust and intake),
the timing chain and the camshaft caps.
Refer to “CAMSHAFTS” section in the
CHAPTER 4.
T R..
Bolt (camshaft cap):
10 Nm (1.0 m • kg, 7.2 ft • lb)

3 - 22
INSP
ADJ
6. Install:
All removed parts
NOTE:
Install all removed parts in reversed order of
their removal. Note the following points.
Install the timing chain tensioner.
Refer to “CAMSHAFTS” section in the
CHAPTER 4.
NOTE:
Turn the crankshaft counterclockwise sev-
eral turns so that the installed parts settle
into the right position.
Recheck the valve clearance.
If the clearance is still incorrect, repeat all
the clearance adjustment steps until the
specified clearance is obtained.
VALVE CLEARANCE ADJUSTMENT

3 - 23
INSP
ADJ
VALVE CLEARANCE ADJUSTMENT
INTAKE
MEASURED
CLEARANCEINSTALLED PAD NUMBER
120 125 130 135 140 145 150 155 160 165 170
175 180 185 190 195 200 205 210 215 220 225 230 235 240
0.00 ~ 0.04 120 125 130 135 140 145 150 155
160165 170 175 180 185 190 195 200 205 210 215 220 225 230
0.05 ~ 0.09
120 125 130 135 140 145 150 155 160 165170 175 180 185 190 195 200 205 210 215 220 225 230 235
0.10 ~ 0.15
STANDARD CLEARANCE
0.16 ~ 0.20125130135140145150155160165170175180 185 190 195 200 205 210 215 220 225 230 235240
0.21 ~ 0.25130135140145150155160165170175180185 190 195 200 205 210 215 220 225 230 235240
0.26 ~ 0.30 135 140 145 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225 230 235240
0.31 ~ 0.35 140 145 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225 230 235240
0.36 ~ 0.40 145 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225 230 235240
0.41 ~ 0.45 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225 230 235240
0.46 ~ 0.50 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225 230 235240
0.51 ~ 0.55 160 165 170 175 180 185 190 195 200 205 210 215 220 225 230 235240
0.56 ~ 0.60 165 170 175 180 185 190 195 200 205 210 215 220 225 230 235240
0.61 ~ 0.65 170 175 180 185 190 195 200 205 210 215 220 225 230 235240
0.66 ~ 0.70 175 180 185 190 195 200 205 210 215 220 225 230 235240
0.71 ~ 0.75 180 185 190 195 200 205 210 215 220 225 230 235240
0.76 ~ 0.80 185 190 195 200 205 210 215 220 225 230 235240VALVE CLEARANCE (cold):
0.10 ~ 0.15 mm
Example: Installed is 175
Measured clearance is 0.22 mm
Replace 175 pad with 185 pad
Pad number: (example)
Pad No. 175 = 1.75 mm
Pad No. 185 = 1.85 mm0.81 ~ 0.85 190 195 200 205 210 215 220 225 230 235240
0.86 ~ 0.90 195 200 205 210 215 220 225 230 235240
0.91 ~ 0.95 200 205 210 215 220 225 230 235240
0.96 ~ 1.00 205 210 215 220 225 230 235240
1.01 ~ 1.05 210 215 220 225 230 235240
1.06 ~ 1.10 215 220 225 230 235240
1.11 ~ 1.15 220 225 230 235240
1.16 ~ 1.20 225 230 235240
1.21 ~ 1.25 230 235240
1.26 ~ 1.30 235240
1.31 ~ 1.35 240
EXHAUST
MEASURED
CLEARANCEINSTALLED PAD NUMBER
120 125 130 135 140 145 150 155 160 165 170
175 180 185 190 195 200 205 210 215 220 225 230 235 240
0.00 ~ 0.04 120 125 130 135 140 145
150155 160 165 170 175 180 185 190 195 200 205 210 215 220
0.05 ~ 0.09
120 125 130 135 140 145 150 155160 165 170 175 180 185 190 195 200 205 210 215 220 225
0.10 ~ 0.14
120 125 130 135 140 145 150 155 160165 170 175 180 185 190 195 200 205 210 215 220 225 230
0.15 ~ 0.19120125130135140145150155160165170 175 180 185 190 195 200 205 210 215 220 225230235
0.20 ~ 0.25
STANDARD CLEARANCE
0.26 ~ 0.30 125 130 135 140 145 150 155 160 165 170 175180 185 190 195 200 205 210 215 220 225230235240
0.31 ~ 0.35130135140145150155160165170175180185 190 195 200 205 210 215 220 225230235240
0.36 ~ 0.40 135 140 145 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225230235240
0.41 ~ 0.45 140 145 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225230235240
0.46 ~ 0.50 145 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225230235240
0.51 ~ 0.55 150 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225230235240
0.56 ~ 0.60 155 160 165 170 175 180 185 190 195 200 205 210 215 220 225230235240
0.61 ~ 0.65 160 165 170 175 180 185 190 195 200 205 210 215 220 225230235240
0.66 ~ 0.70 165 170 175 180 185 190 195 200 205 210 215 220 225230235240
0.71 ~ 0.75 170 175 180 185 190 195 200 205 210 215 220 225230235240
0.76 ~ 0.80 175 180 185 190 195 200 205 210 215 220 225230235240
0.81 ~ 0.85 180 185 190 195 200 205 210 215 220 225230235240
0.86 ~ 0.90 185 190 195 200 205 210 215 220 225230235240
VALVE CLEARANCE (cold):
0.20 ~ 0.25 mm
Example: Installed is 175
Measured clearance is 0.32 mm
Replace 175 pad with 185 pad
Pad number: (example)
Pad No. 175 = 1.75 mm
Pad No. 185 = 1.85 mm0.91 ~ 0.95 190 195 200 205 210 215 220 225230235240
0.96 ~ 1.00 195 200 205 210 215 220 225230235240
1.01 ~ 1.05 200 205 210 215 220 225230235240
1.06 ~ 1.10 205 210 215 220 225230235240
1.11 ~ 1.15 210 215 220 225230235240
1.16 ~ 1.20 215 220 225230235240
1.21 ~ 1.25 220 225230235240
1.26 ~ 1.30 225230235240
1.31 ~ 1.35 230235240
1.36 ~ 1.40 235240
1.41 ~ 1.45 240

4 - 23
ENGCAMSHAFTS
REMOVAL POINTS
Camshaft
1. Remove:
Timing plug 1
Straight plug 2
2. Align:
“I” mark
With stationary pointer.
Checking steps:
Turn the crankshaft counterclockwise with
a wrench.
Align the “I” mark a on the rotor with the
stationary pointer b on the crankcase
cover. When the “I” mark is aligned with
the stationary pointer, the piston is at the
Top Dead Center (T.D.C.).
NOTE:
In order to be sure that the piston is at Top
Dead Center, the punch mark c on the
exhaust camshaft and the punch mark d
on the intake camshaft must align with the
cylinder head surface, as shown in the
illustration.
If there is no clearance, rotate the crank-
shaft counterclockwise one turn.
3. Loosen:
Tensioner cap bolt 1
4. Remove:
Timing chain tensioner 2
5. Remove:
Bolt (camshaft cap) 1
Camshaft caps 2
NOTE:
Remove the bolts (camshaft cap) in a criss-
cross pattern, working from the outside in.
CAUTION:
The bolts (camshaft cap) must be removed
evenly to prevent damage to the cylinder
head, camshafts or camshaft caps.
1
2
1
2

4 - 25
ENGCAMSHAFTS
4. Measure:
Camshaft-to-cap clearance
Out of specification → Measure cam-
shaft journal diameter.
Camshaft-to-cap clearance:
0.020 ~ 0.054 mm
(0.0008 ~ 0.0021 in)
: 0.08 mm (0.003 in)
Measurement steps:
Install the camshaft onto the cylinder
head.
Position a strip of Plastigauge® 1 onto the
camshaft.
Install the circlip, dowel pins and camshaft
caps.
T R..
Bolt (camshaft cap):
10 Nm (1.0 m • kg, 7.2 ft • lb)
NOTE:
Tighten the bolts (camshaft cap) in a criss-
cross pattern from innermost to outer
caps.
Do not turn the camshaft when measuring
clearance with the Plastigauge®.
Remove the camshaft caps and measure
the width of the Plastigauge
® 1.
5. Measure:
Camshaft journal diameter a
Out of specification → Replace the
camshaft.
Within specification → Replace cam-
shaft case and camshaft caps as a set.
Camshaft sprocket
1. Inspect:
Camshaft sprocket 1
Wear/damage → Replace the camshaft
assembly and timing chain as a set.
Camshaft journal diameter:
21.967 ~ 21.980 mm
(0.8648 ~ 0.8654 in)