2001 YAMAHA WR 426F length

4 - 38
ENGVALVES AND VALVE SPRINGS
Valve spring
1. Measure:
lValve spring free length a
Out of specification ® Replace.
2. Measure:
lCompressed spring force a
Out of specification ® Replace.
bInstalled length
Free length (valve spring):
Intake:
41.36 mm (1.63 in)
: 39.3 mm (1.55 in)
Exhaust:
43.60 mm (1.72 in)
: 41.4 mm (1.63 in)
Compressed spring force:
Intake:
11.5 ~ 13.2 kg at 32.87 mm
(25.35 ~ 29.10 lb at 1.29 in)
Exhaust:
11.9 ~ 13.7 kg at 35.38 mm
(26.23 ~ 30.20 lb at 1.39 in)
3. Measure:
lSpring tilt a
Out of specification ® Replace.
Spring tilt limit:
Intake:
2.5˚/1.8 mm (0.071 in)
Exhaust:
2.5˚/1.9 mm (0.075 in)
Valve lifter
1. Inspect:
lValve lifter
Scratches/damage ® Replace both lift-
ers and cylinder head.

4 - 50
ENGCLUTCH (WR426F)
EC493000
REMOVAL POINTS
EC483211
Clutch boss
1. Remove:
lNut 1
lLock washer 2
lClutch boss 3
NOTE:
Straighten the lock washer tab and use the
clutch holding tool 4 to hold the clutch boss.
For USA and CDN
õExcept for USA and CDN
Clutch holding tool:
YM-91042/90890-04086

õ
EC494000
INSPECTION
EC484100
Clutch housing and boss
1. Inspect:
lClutch housing 1
Cracks/wear/damage ® Replace.
lClutch boss 2
Scoring/wear/damage ® Replace.
EC484201
Primary driven gear
1. Check:
lCircumferential play
Free play exists ® Replace.
lGear teeth a
Wear/damage ® Replace.
EC484400
Clutch spring
1. Measure:
lClutch spring free length a
Out of specification ® Replace springs
as a set.
Clutch spring free length:
Standard
48.4 mm (1.91 in) 47.4 mm (1.87 in)

4 - 57
ENGCLUTCH (WR400F)
EC493000
REMOVAL POINTS
EC483211
Clutch boss
1. Remove:
lNut 1
lLock washer 2
lClutch boss 3
NOTE:
Straighten the lock washer tab and use the
clutch holding tool 4 to hold the clutch boss.
For USA and CDN
õExcept for USA and CDN
Clutch holding tool:
YM-91042/90890-04086
õ
EC494000
INSPECTION
EC484100
Clutch housing and boss
1. Inspect:
lClutch housing 1
Cracks/wear/damage ® Replace.
lClutch boss 2
Scoring/wear/damage ® Replace.
EC484201
Primary driven gear
1. Check:
lCircumferential play
Free play exists ® Replace.
lGear teeth a
Wear/damage ® Replace.
EC484400
Clutch spring
1. Measure:
lClutch spring free length a
Out of specification ® Replace springs
as a set.
Clutch spring free length:
Standard
44 mm (1.73 in) 43 mm (1.69 in)

5 - 32
CHAS
EC554200
Base valve
1. Inspect:
lValve assembly 1
Wear/damage ® Replace.
lO-ring 2
Damage ® Replace.
EC554400
Fork spring
1. Measure:
lFork spring free length a
Out of specification ® Replace.
EC554502
Inner tube
1. Inspect:
lInner tube surface a
Score marks ® Repair or replace.
Use #1,000 grit wet sandpaper.
Damaged oil lock piece ® Replace.
lInner tube bends
Out of specification ® Replace.
Use the dial gauge 1.
NOTE:
The bending value is shown by one half of the
dial gauge reading.
WARNING
Do not attempt to straighten a bent inner
tube as this may dangerously weaken the
tube.
EC554600
Outer tube
1. Inspect:
lOuter tube 1
Score marks/wear/damage ® Replace.
Fork spring free length:
Standard
460 mm
(18.1 in)455 mm
(17.9 in)
Inner tube bending limit:
0.2 mm (0.008 in)
FRONT FORK

5 - 64
CHASREAR SHOCK ABSORBER
2. Tighten:
lAdjuster 1
3. Adjust:
lSpring length (installed) a
* For EUROPE
NOTE:
The length of the spring (installed) changes
1.5 mm (0.06 in) per turn of the adjuster.
CAUTION:
Never attempt to turn the adjuster beyond
the maximum or minimum setting.
Spring length (installed) a:
Standard
lengthExtent of
adjustment
241 mm (9.49 in)
*244 mm (9.61 in)240.5 ~ 258.5 mm
(9.47 ~ 10.18 in)
4. Tighten:
lLocknut 1
Rear shock absorber
1. Install:
lDust seal 1
lO-ring 2
lCollar 3
NOTE:
lApply the molybdenum disulfide grease on
the bearing.
lApply the lithium soap base grease on the
dust seals, O-rings and collars.
New

7 - 17
TUN
EC72B000
Rear suspension setting
The rear suspension setting should be made
depending on the rider’s feeling of an actual
run and the circuit conditions.
The rear suspension setting includes the fol-
lowing two factors:
1. Setting of spring preload
lChange the set length of the spring.
lChange the spring.
2. Setting of damping force
lChange the rebound damping.
lChange the compression damping.
EC72C001
Choosing set length
1. Place a stand or block under the engine
to put the rear wheel above the floor, and
measure the length a between the rear
wheel axle center and the rear fender
holding bolt.
2. Remove the stand or block from the
engine and with a rider astride the seat,
measure the sunken length b between
the rear wheel axle center and the rear
fender holding bolt.
3. Loosen the locknut 1 and make adjust-
ment by turning the spring adjuster 2 to
achieve the standard figure from the sub-
traction of the length b from the length
a.
Standard figure:
90 ~ 100 mm (3.5 ~ 3.9 in)
SETTING

7 - 18
TUN
NOTE:
lIf the machine is new and after it is broken in,
the same set length of the spring may
change because of the initial fatigue, etc. of
the spring. Therefore, be sure to make re-
evaluation.
lIf the standard figure cannot be achieved by
adjusting the spring adjuster and changing
the spring set length, replace the spring with
an optional one and make re-adjustment.
EC72G001
Setting of spring after replacement
After replacement, be sure to adjust the spring
to the set length and [sunken length 90 ~
100 mm (3.5 ~ 3.9 in)] set it.
1. Use of soft spring
lSet the soft spring for less rebound
damping to compensate for its less
spring load. Run with the rebound
damping adjuster one or two clicks on
the softer side and readjust it to suit
your preference.
2. Use of stiff spring
lSet the soft spring for more rebound
damping to compensate for its greater
spring load. Run with the rebound
damping adjuster one or two clicks on
the stiffer side and readjust it to suit
your preference.
*Adjusting the rebound damping will be
followed more or less by a change in the
compression damping. For correction,
turn the low compression damping
adjuster on the softer side.
SETTING

7 - 19
TUNSETTING
CAUTION:
When using a rear cushion other than cur-
rently installed, use the one whose overall
length a does not exceed the standard as
it may result in faulty performance. Never
use one whose overall length is greater
than standard.
Coverage of spring by weight
õRider weight
1Soft
2Standard
3Stiff
Length a of standard shock:
485.5 mm (19.11 in)