length YAMAHA YZ426F 2002 User Guide

4 - 23
ENGCAMSHAFTS
6. Remove:
Clips
Exhaust camshaft 1
Intake camshaft 2
NOTE:
Attach a wire 3 to the timing chain to prevent
it from falling into the crankcase.
INSPECTION
Camshaft
1. Inspect:
Cam lobes
Pitting/scratches/blue discoloration →
Replace.
2. Measure:
Cam lobes length a and b
Out of specification → Replace.
Cam lobes length:
Intake:
a31.7 ~ 31.8 mm
(1.2480 ~ 1.2520 in)
: 31.6 mm (1.244 in)
b22.95 ~ 23.05 mm
(0.9035 ~ 0.9075 in)
: 22.85 mm (0.900 in)
Exhaust:
a31.2 ~ 31.3 mm
(1.2283 ~ 1.2323 in)
: 31.1 mm (1.224 in)
b22.95 ~ 23.05 mm
(0.9035 ~ 0.9075 in)
: 22.85 mm (0.900 in)
3. Measure:
Runout (camshaft)
Out of specification → Replace.
Runout (camshaft):
Less than 0.03 mm (0.0012 in)

4 - 37
ENGVALVES AND VALVE SPRINGS
Valve spring
1. Measure:
Valve spring free length a
Out of specification → Replace.
2. Measure:
Compressed 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:
Spring 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:
Valve lifter
Scratches/damage → Replace both lift-
ers and cylinder head.

4 - 48
ENGCLUTCH
EC493000
REMOVAL POINTS
EC483211
Clutch boss
1. Remove:
Nut 1
Lock washer 2
Clutch boss 3
NOTE:
Straighten the lock washer tab and use the
clutch holding tool 4 to hold the clutch boss.
ÅFor USA and CDN
ıExcept for USA and CDN
Clutch holding tool:
YM-91042/90890-04086
Å
ı
EC494000
INSPECTION
EC484100
Clutch housing and boss
1. Inspect:
Clutch housing 1
Cracks/wear/damage → Replace.
Clutch boss 2
Scoring/wear/damage → Replace.
EC484201
Primary driven gear
1. Check:
Circumferential play
Free play exists → Replace.
Gear teeth a
Wear/damage → Replace.
EC484400
Clutch spring
1. Measure:
Clutch 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:

Valve assembly
1

Wear/damage
→
Replace.

O-ring
2

Damage
→
Replace.
EC554400
Fork spring
1. Measure:

Fork spring free length
a

Out of specification
→
Replace.
EC554502
Inner tube
1. Inspect:

Inner tube surface
a

Score marks
→
Repair or replace.
Use #1,000 grit wet sandpaper.
Damaged oil lock piece
→
Replace.

Inner 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:

Outer 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 - 63
CHASREAR SHOCK ABSORBER
2. Tighten:
Adjuster 1
3. Adjust:
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:
Locknut 1
Rear shock absorber
1. Install:
Dust seal 1
O-ring 2
Collar 3
NOTE:
Apply the molybdenum disulfide grease on
the bearing.
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)245.5 ~ 263.5 mm
(9.67 ~ 10.37 in)
*255.5 ~ 273.5 mm
(10.06 ~ 10.77 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
Change the set length of the spring.
Change the spring.
2. Setting of damping force
Change the rebound damping.
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

7 - 17
TUNSETTING
NOTE:
If 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.
If 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 [sunken length 90 ~ 100 mm
(3.5 ~ 3.9 in)] and set it.
1. Use of soft spring
Set 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
Set 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.

7 - 18
TUN
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.
ÅCoverage of spring by weight
ıRider weight
1Soft
2Standard
3Stiff
Length a of standard shock:
490.5 mm (19.31 in)
SETTING

7 - 19
TUNSETTING
EC72Q000
Rear shock absorber setting parts
Rear shock spring 1
[Equal pitch spring]
[Unequal pitch spring]
*For EUROPE
NOTE:
The unequal pitch spring is softer in initial
characteristic than the equal pitch spring and
is difficult to bottom out under full compres-
sion.
The I.D. color a is marked at the end of the
spring.
Extent of adjustment (spring length)
TYPESPRING
RATESPRING
PART NUMBERI.D.
COLOR/
POINTSPRING
FREE
LENGTH
SOFT4.4
4.6
4.8
5.0
5.25DH-22212-70
5DH-22212-10
5DH-22212-20
5DH-22212-30
5DH-22212-40Brown/1
Green/1
Red/1
Black/1
Blue/1260
260
260
260
260
STD 5.4 5DH-22212-50 Yellow/1 265
STIFF 5.65DH-22212-60 Pink/1 265
TYPESPRING
RATE
(approx.)SPRING
PART NUMBERI.D.
COLOR/
POINTSPRING
FREE
LENGTH
SOFT4.6
4.8
5.0
5.25ET-22212-20
5ET-22212-00
5ET-22212-10
5ET-22212-30Green/2
Red/2
Black/2
Blue/2275
275
275
275
*STD 5.4 5ET-22212-40 Yellow/2 275
STIFF 5.65ET-22212-50 Pink/2 280
SPRING FREE
LENGTHEXTENT OF
ADJUSTMENT b
260 mm (10.24 in)240.5 ~ 258.5 mm
(9.47 ~ 10.18 in)
265 mm (10.43 in)245.5 ~ 263.5 mm
(9.67 ~ 10.37 in)
275 mm (10.83 in)255.5 ~ 273.5 mm
(10.06 ~ 10.77 in)
280 mm (11.02 in)260.5 ~ 278.5 mm
(10.26 ~ 10.96 in)

7 - 20
TUNSETTING
EC72H002
Suspension setting
Front fork
NOTE:
If any of the following symptoms is experienced with the standard position as the base, make
resetting by reference to the adjustment procedure given in the same chart.
Before any change, set the rear shock absorber sunken length to the standard figure 90 ~
100 mm (3.5 ~ 3.9 in).
SymptomSection
Check Adjust
JumpLarge
gapMedium
gapSmall
gap
Stiff over entire range

Compression damping
Oil level (oil amount)
SpringTurn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Decrease oil level by about 5 ~ 10 mm (0.2 ~ 0.4 in).
Replace with soft spring.
Unsmooth movement
over entire range

Outer tube
Inner tube
Under bracket tightening
torqueCheck for any bends, dents, and other noticeable
scars, etc. If any, replace affected parts.
Retighten to specified torque.
Poor initial
movement

Rebound damping
Oil sealTurn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Apply grease in oil seal wall.
Soft over entire range,
bottoming out

Compression damping
Oil level (oil amount)
SpringTurn adjuster clockwise (about 2 clicks) to increase
damping.
Increase oil level by about 5 ~ 10 mm (0.2 ~ 0.4 in).
Replace with stiff spring.
Stiff toward stroke end
Oil level (oil amount) Decrease oil level by about 5 mm (0.2 in).
Soft toward stroke end,
bottoming out
Oil level (oil amount) Increase oil level by about 5 mm (0.2 in).
Stiff initial movement
Compression dampingTurn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Low front, tending to
lower front posture

Compression damping
Rebound damping
Balance with rear end
Oil level (oil amount)Turn adjuster clockwise (about 2 clicks) to increase
damping.
Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Set sunken length for 95 ~ 100 mm (3.7 ~ 3.9 in) when
one passenger is astride seat (lower rear posture).
Increase oil level by about 5 mm (0.2 in).
“Obtrusive” front, tend-
ing to upper front pos-
ture

Compression damping
Balance with rear end
Spring
Oil lever (oil amount)Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Set sunken length for 90 ~ 95 mm (3.5 ~ 3.7 in) when
one passenger is astride seat (upper rear posture).
Replace with soft spring.
Decrease oil level by about 5 ~ 10 mm (0.2 ~ 0.4 in).