2001 YAMAHA YZ426F length

3 - 31
INSP
ADJ
SPROCKETS INSPECTION/DRIVE CHAIN INSPECTION
EC368000
SPROCKETS INSPECTION
1. Inspect:
lSprocket teeth a
Excessive wear ® Replace.
NOTE:
Replace the drive, driven sprockets and drive
chain as a set.
EC369002
DRIVE CHAIN INSPECTION
1. Remove:
lMaster link clip
lJoint 1
lDrive chain 2
2. Clean:
lDrive chain
Place it in kerosene, and brush off as
much dirt as possible. Then remove the
chain from the kerosene and dry the
chain.
3. Measure:
lDrive chain length (10 links) a
Out of specification ® Replace.
Drive chain length (10 links):
Limit: 152.5 mm (6.00 in)
4. Check:
lDrive chain stiffness a
Clean and oil the chain and hold as
illustrated.
Stiff ® Replace drive chain.

3 - 37
INSP
ADJREAR SHOCK ABSORBER SPRING PRELOAD
ADJUSTMENT
EC36M013
REAR SHOCK ABSORBER SPRING
PRELOAD ADJUSTMENT
1. Elevate the rear wheel by placing the
suitable stand under the engine.
2. Remove:
lRear frame
3. Loosen:
lLocknut 1
4. Adjust:
lSpring preload
By turning the adjuster 2.
* For EUROPE
NOTE:
lBe sure to remove all dirt and mud from
around the locknut and adjuster before
adjustment.
lThe 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.
5. Tighten:
lLocknut
6. Install:
lRear frame Stiffer ®Increase the spring preload.
(Turn the adjuster 2 in.)
Softer ®Decrease the spring preload.
(Turn the adjuster 2 out.)
Spring length (installed) a:
Standard lengthExtent of adjustment
248 mm (9.76 in)
*262 mm (10.31 in)247 ~ 265 mm
(9.72 ~ 10.43 in)
*257 ~ 275 mm
(10.12 ~ 10.83 in)
T R..29 Nm (2.9 m · kg, 21 ft · lb)

4 - 22
ENG

CAMSHAFTS
6. Remove:
l
Clips
l
Dowel pins
l
Exhaust camshaft
1

l
Intake camshaft
2

NOTE:

Attach a wire
3
to the timing chain to prevent
it from falling into the crankcase.
INSPECTION
Camshaft
1. Inspect:
l
Cam lobes
Pitting/scratches/blue discoloration
®

Replace.
2. Measure:
l
Cam lobes length
a
and
b

Out of specification
®
Replace.
Cam lobes length:
Intake:
a
31.7 ~ 31.8 mm
(1.2480 ~ 1.2520 in)
: 31.6 mm (1.244 in)
b
22.95 ~ 23.05 mm
(0.9035 ~ 0.9075 in)
: 22.85 mm (0.900 in)
Exhaust:
a
31.2 ~ 31.3 mm
(1.2283 ~ 1.2323 in)
: 31.1 mm (1.224 in)
b
22.95 ~ 23.05 mm
(0.9035 ~ 0.9075 in)
: 22.85 mm (0.900 in)
3. Measure:
l
Runout (camshaft)
Out of specification
®
Replace.
Runout (camshaft):
Less than 0.03 mm (0.0012 in)

4 - 36
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 - 47
ENGCLUTCH
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
50 mm (1.97 in) 49 mm (1.93 in)

5 - 31
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 Limit
460 mm (18.1 in) 455 mm (17.9 in)
Inner tube bending limit:
0.2 mm (0.008 in)
FRONT FORK

5 - 62
CHAS

REAR SHOCK ABSORBER
2. Tighten:
l
Adjuster
1

3. Adjust:
l
Spring length (installed)
a

* For EUROPE
NOTE:

The length of the spring (installed) changes
1.5 mm (0.06 in) per turn of the adjuster.
ACHTUNG:CAUTION:

Never attempt to turn the adjuster beyond
the maximum or minimum setting.
4. Tighten:
l
Locknut
1

Rear shock absorber
1. Install:
l
Dust seal
1

l
O-ring
2

l
Collar
3

NOTE:

l
Apply the molybdenum disulfide grease on
the bearing.
l
Apply the lithium soap base grease on the
dust seals, O-rings and collars.
Spring length (installed)
a
:
Standard
lengthExtent of
adjustment
248 mm (9.76 in)
*262 mm (10.31 in)247 ~ 265 mm
(9.72 ~ 10.43 in)
*257 ~ 275 mm
(10.12 ~ 10.83 in)
New

7 - 16
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
l
Change the set length of the spring.
l
Change the spring.
2. Setting of damping force
l
Change the rebound damping.
l
Change 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