2002 YAMAHA WR 426F light

4 - 17
ENGCARBURETOR
10. Install:
Starter jet 1
Pilot jet 2
Spacer 3
Needle jet 4
Main jet 5
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
* Except for USANote 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:
WR426F: 1-5/8 turns out
*1-1/8 turns out
WR400F: 1-1/2 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
ÅWR426F
ıWR400F Å

4 - 19
ENG

CARBURETOR
19. Install:

Carburetor breather hose
1

Refer to “CABLE ROUTING DIA-
GRAM” section in the CHAPTER 2.
NOTE:

Install the breather hose to the carburetor so
that the hose does not bend near where it is
installed.
Å
WR426F
ı
WR400F
Å
1
1
ı
11

Accelerator pump timing adjustment
* Except for USA
Adjustment steps:
NOTE:

In order for the throttle valve height
a
to
achieve the specified value, tuck under the
throttle valve plate
1
the rod
2
etc. with the
same outer diameter as the specified value.
Throttle valve height:
WR426F: 3.10 mm (0.122 in)
*2.25 mm (0.089 in)
WR400F: 6.60 mm (0.260 in)

Fully turn in the accelerator pump adjust-
ing screw
3
.

Check that the link lever
4
has free play
b
by pushing lightly on it.

Gradually turn out the adjusting screw
while moving the link lever until it has no
more free play.

4 - 27
ENGCAMSHAFTS
Timing chain tensioner
1. Check:
While pressing the tensioner rod lightly
with fingers, use a thin screwdriver 1
and wind the tensioner rod up fully
clockwise.
When releasing the screwdriver by
pressing lightly with fingers, make sure
that the tensioner rod will come out
smoothly.
If not, replace the tensioner assembly.
ASSEMBLY AND INSTALLATION
1. Install:
Exhaust camshaft 1
Intake camshaft 2
Installation steps:
Turn the crankshaft counterclockwise until
the “I” mark a on the rotor is aligned with
the stationary pointer b on the crankcase
cover.
Fit the timing chain 3 onto both camshaft
sprockets and install the camshafts on the
cylinder head.
NOTE:
The camshafts should be installed onto the
cylinder head so that the exhaust cam
sprocket punch mark c and the intake cam
sprocket punch mark d align with the sur-
face of the cylinder head.
CAUTION:
Do not turn the crankshaft during the
camshaft installation. Damage or
improper valve timing will result.

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ENG

CAMSHAFTS
2. Install:

Timing chain tensioner
3. Turn:

Crankshaft
Counterclockwise several turns
4. Check:

Rotor “I” mark
Align with the crankcase stationary
pointer.

Camshaft match marks
Align with the cylinder head surface.
Out of alignment
→
Adjust.

Install the clips and camshaft caps
4
.
T R..

Bolt (camshaft cap):
10 Nm (1.0 m • kg, 7.2 ft • lb)
NOTE:

Tighten the bolts (camshaft cap)
5
in a
crisscross pattern.
CAUTION:

The bolts (camshaft cap) must be tight-
ened evenly, or damage to the cylinder
head, camshaft caps, and camshaft will
result.
Installation steps:

While pressing the tensioner rod lightly
with fingers, use a thin screwdriver and
wind the tensioner rod up fully clockwise.

With the rod fully wound and the chain
tensioner UP mark
a
facing upward,
install the gasket
1
and the chain ten-
sioner
2
, and tighten the bolt
3
to the
specified torque.
T R..

Bolt (timing chain tensioner):
10 Nm (1.0 m • kg, 7.2 ft • lb)

Release the screwdriver, check the ten-
sioner rod to come out and tighten the
gasket
4
and the cap bolt
5
to the speci-
fied torque.
T R..

Tensioner cap bolt:
7 Nm (0.7 m • kg, 5.1 ft • lb)

4 - 38
ENGVALVES AND VALVE SPRINGS
9. Lap:
Valve face
Valve seat
NOTE:
After refacing the valve seat or replacing the
valve and valve guide, the valve seat and
valve face should be lapped.
Lapping steps:
Apply a coarse lapping compound to the
valve face.
CAUTION:
Do not let the compound enter the gap
between the valve stem and the guide.
Apply molybdenum disulfide oil to the
valve stem.
Install the valve into the cylinder head.
Turn the valve until the valve face and
valve seat are evenly polished, then clean
off all of the compound.
NOTE:
For best lapping results, lightly tap the valve
seat while rotating the valve back and forth
between your hands.
Apply a fine lapping compound to the
valve face and repeat the above steps.
NOTE:
After every lapping operation be sure to
clean off all of the compound from the valve
face and valve seat.
Apply Mechanic’s blueing dye (Dykem) to
the valve face.
Install the valve into the cylinder head.
Press the valve through the valve guide
and onto the valve seat to make a clear
pattern.
Measure the valve seat width again. If the
valve seat width is out of specification,
reface and relap the valve seat.

4 - 40
ENG

VALVES AND VALVE SPRINGS
Combination of cylinder head and valve
lifter
1. Combination:
For this combination, match the paint
color on the cylinder head with that on
the valve lifter according to the chart
below.
NOTE:

When you purchase a cylinder head, you can-
not designate its size. Choose the valve lifter
that matches the above chart.
Combination
Cylinder head mark
a
(color)Valve lifter mark
b
(color)
Blue Blue
Yellow Yellow
Purple Black
ASSEMBLY AND INSTALLATION
1. Apply:

Molybdenum disulfide oil
Onto the valve stem and valve stem
seal.
2. Install:

Valves
1


Valve spring seats
2


Valve stem seals
3


Valve springs
4


Valve spring retainers
5

NOTE:


Make sure that each valve is installed in its
original place, also referring to the painted
color as follows.
Intake (middle)
a
: light blue
Intake (right/left)
b
: white
Exhaust: not paint

Install the valve springs with the larger pitch
c
facing upward.
d
Smaller pitch
New

4 - 41
ENG
3. Install:
Valve cotters
NOTE:
While compressing the valve spring with a
valve spring compressor 1 install the valve
cotters.
4. To secure the valve cotters onto the
valve stem, lightly tap the valve tip with a
piece of wood.
CAUTION:
Hitting the valve tip with excessive force
could damage the valve.
Valve spring compressor:
YM-4019/90890-04019
5. Install:
Adjusting pad 1
Valve lifter 2
NOTE:
Apply the engine oil on the valve lifters.
Apply the molybdenum disulfide oil on the
valve stem end.
Valve lifter must turn smoothly when rotated
with a finger.
Be careful to reinstall valve lifters and pads
in their original place.
VALVES AND VALVE SPRINGS

4 - 96
ENGCRANKCASE AND CRANKSHAFT
REMOVAL POINTS
Crankcase
1. Separate:
Crankcase (right)
Crankcase (left)
Separation steps:
Remove the crankcase bolts, hose guide
and clutch cable holder.
NOTE:
Loosen each bolt 1/4 of a turn at a time and
after all the bolts are loosened, remove
them.
Remove the crankcase (right).
NOTE:
Place the crankcase with its left side
downward and split it by inserting a screw-
driver tip into the splitting slit a in the
crankcase.
Lift the crankcase (right) horizontally while
lightly patting the case splitting slit and
engine mounting boss using a soft ham-
mer, and leave the crankshaft and trans-
mission with the crankcase (left).
CAUTION:
Use soft hammer to tap on the case half.
Tap only on reinforced portions of case.
Do not tap on gasket mating surface.
Work slowly and carefully. Make sure the
case halves separate evenly. If one end
“hangs up”, take pressure off the push
screw, realign, and start over. If the
cases do not separate, check for a
remaining case screw or fitting. Do not
force.
Remove the dowel pins and O-ring.
a