2002 YAMAHA YZ426F valve

3 - 7
INSP
ADJ
RADIATOR CAP INSPECTION
CAUTION:
Do not mix more than one type of ethyl-
ene glycol antifreeze containing corro-
sion inhibitors for aluminum engine.
Do not use water containing impurities or
oil.
7. Install:
Radiator cap
Start the engine and warm it up for a
several minutes.
8. Check:
Coolant level
Coolant level low → Add coolant. Handling notes of coolant:
The coolant is harmful so it should be han-
dled with special care.
WARNING
When coolant splashes to your eye.
Thoroughly wash your eye with water
and see your doctor.
When coolant splashes to your clothes.
Quickly wash it away with water and
then with soap.
When coolant is swallowed.
Quickly make him vomit and take him
to a doctor.
EC355000
RADIATOR CAP INSPECTION
1. Inspect:
Seal (radiator cap) 1
Valve and valve seat 2
Crack/damage → Replace.
Exist fur deposits 3 → Clean or
replace.

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:
1,700 ~ 1,900 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.
NOTE:
Squeezing the decompressor lever allows
the crankshaft to be turned easily.
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 (intake 1 and
exhaust 2).
NOTE:
Attach a wire 3 to the timing chain to pre-
vent it from falling into the crankcase.
Remove the decompression guide 4,
cable 5, bolt 6 and decompression shaft
7.
Remove the valve lifters 8 and the pads
9.
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.

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.