valve YAMAHA YZ426F 2002 Owner's Manual

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
measured 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 0 and the valve lift-
ers A.
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 decompression shaft B, plain
washer C, bolt D, guide E, bolt F and
decompression cable G.
NOTE:
Apply the engine oil on the decompression
shaft.
T R..
Bolt (decompression shaft):
7 Nm (0.7 m • kg, 5.1 ft • lb)
Bolt (guide):
10 Nm (1.0 m • kg, 7.2 ft • lb)

3 - 22
INSP
ADJ
VALVE CLEARANCE ADJUSTMENT
6. Install:
All removed parts
NOTE:
Install all removed parts in reversed order of
their removal. Note the following points.
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)
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.

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

3 - 41
INSP
ADJTIRE PRESSURE CHECK/SPOKES INSPECTION AND
TIGHTENING/WHEEL INSPECTION
EC36Q000
TIRE PRESSURE CHECK
1. Measure:
Tire pressure
Out of specification → Adjust.
NOTE:
Check the tire while it is cold.
Loose bead stoppers allow the tire to slip off
its position on the rim when the tire pressure
is low.
A tilted tire valve stem indicates that the tire
slips off its position on the rim.
If the tire valve stem is found tilted, the tire is
considered to be slipping off its position. Cor-
rect the tire position.
Standard tire pressure:
100 kPa (1.0 kgf/cm2, 15 psi)
EC36S002
SPOKES INSPECTION AND TIGHTENING
1. Inspect:
Spokes 1
Bend/damage → Replace.
Loose spoke → Retighten.
2. Tighten:
Spokes
NOTE:
Be sure to retighten these spokes before and
after break-in. After a practice or a race check
spokes for looseness.
T R..3 Nm (0.3 m · kg, 2.2 ft · lb)
EC36T000
WHEEL INSPECTION
1. Inspect:
Wheel runout
Elevate the wheel and turn it.
Abnormal runout → Replace.

4 - 8
ENGCARBURETOR
CARBURETOR DISASSEMBLY
Extent of removal:1 Carburetor disassembly
Extent of removal Order Part name Q’ty Remarks
CARBURETOR DISASSEMBLY
1Breather hose 4
2Valve lever housing cover 1
3Screw (throttle shaft) 1
4Throttle valve 1
5Needle holder 1
6Jet needle 1
7Cover 1
8Spring 1
9Diaphragm (accelerator pump) 1
0Float chamber 1
APilot screw 1 Refer to “REMOVAL POINTS”.
BFloat pin 1
CFloat 1
DNeedle valve 1
EValve seat 1
1

4 - 11
ENGCARBURETOR
2. Inspect:
Main jet 1
Pilot jet 2
Needle jet 3
Starter jet 4
Main air jet 5
Pilot air jet 6
Damage → Replace.
Contamination → Clean.
NOTE:
Use a petroleum based solvent for cleaning.
Blow out all passages and jets with com-
pressed air.
Never use a wire.
EC464210
Needle valve
1. Inspect:
Needle valve 1
Valve seat 2
Grooved wear a → Replace.
Dust b and c → Clean.
NOTE:
Replace the needle valve and valve seat as a
set.
EC464300
Throttle valve
1. Check:
Free movement
Stick → Repair or replace.
Insert the throttle valve 1 into the car-
buretor body, and check for free move-
ment.
EC464400
Jet needle
1. Inspect:
Jet needle 1
Bends/wear → Replace.
Clip groove
Free play exists/wear → Replace.
Clip position
Standard clip position:
No.4 Groove

4 - 12
ENGCARBURETOR
EC464511
Float height
1. Measure:
Float height a
Out of specification → Adjust.
Float height:
8.0 mm (0.31 in)
Measurement and adjustment steps:
Hold the carburetor in an upside down
position.
NOTE:
Slowly tilt the carburetor in the opposite
direction, then take the measurement
when the needle valve aligns with the float
arm.
If the carburetor is level, the weight of the
float will push in the needle valve, result-
ing in an incorrect measurement.
Measure the distance between the mating
surface of the float chamber and top of the
float using a vernier calipers.
NOTE:
The float arm should be resting on the nee-
dle valve, but not compressing the needle
valve.
If the float height is not within specifica-
tion, inspect the valve seat and needle
valve.
If either is worn, replace them both.
If both are fine, adjust the float height by
bending the float tab b on the float.
Recheck the float height.
EC464600
Float
1. Inspect:
Float 1
Damage → Replace.

4 - 15
ENGCARBURETOR
8. Install:
Throttle shaft assembly 1
Plain washer (metal) 2
Plain washer (resin) 3
Valve lever 4
NOTE:
Apply the fluorochemical grease on the bear-
ings.
Fit the projection a on the throttle shaft
assembly into the slot b in the TPS (throttle
position sensor).
Make sure the stopper c of the spring fits
into the recess in the carburetor.
Turn the throttle shaft assembly left while
holding down the lever 1 5 and fit the throt-
tle stop screw tip d to the stopper e of the
throttle shaft assembly pulley.
ab
1
2
3
4
c
e
d
5
9. Install:
Push rod 1
NOTE:
While holding down the lever 1 2, insert the
push rod farthest into the carburetor.12
10. Install:
Starter jet 1
Pilot jet 2
Spacer 3
Needle jet 4
Main jet 5

4 - 16
ENGCARBURETOR
11. Install:
Valve seat
Screw (valve seat) 1
Needle valve 2
Float 3
Float pin 4
NOTE:
After installing the needle valve to the float,
install them to the carburetor.
Check the float for smooth movement.
12. Install:
Pilot screw 1
Spring 2
Washer 3
O-ring 4
Note the following installation points:
Turn in the pilot screw until it is lightly
seated.
Turn out the pilot screw by the number of
turns recorded before removing.
Pilot screw:
1-3/8 turns out (example)
13. Install:
O-ring
Float chamber 1
Screw (float chamber) 2
Cable holder (throttle stop screw cable)
3
Hose holder (carburetor breather hose)
4
14. Install:
Diaphragm (accelerator pump) 1
Spring 2
O-ring 3
Cover 4
Screw (cover) 5
NOTE:
Install the diaphragm (accelerator pump) with
its mark a facing the spring.
421 3
4

4 - 17
ENGCARBURETOR
15. Install:
Jet needle 1
Collar 2
Spring 3
Needle holder 4
Throttle valve plate 5
To throttle valve 6.
5
6
1
2
3
4
16. Install:
Throttle valve assembly 1
Screw (throttle shaft) 2
NOTE:
Install the valve lever rollers 3 into the slits a
of the throttle valve.
17. Install:
O-ring 1
Valve lever housing cover 2
Bolt (valve lever housing cover) 3
18. Install:
Carburetor breather hose 1
Refer to “CABLE ROUTING DIA-
GRAM” section in the CHAPTER 2.