steering YAMAHA YZ450F 2008 User Guide

3-19
CHASSIS
• STANDARD POSITION:
This is the position which is back
by the specific number of clicks
from the fully turned-in position.
(Which align the punch mark "a"
on the adjuster with the punch
mark "b" on the high compression
damping adjuster.)
Do not force the adjuster past the
minimum or maximum extent of
adjustment. The adjuster may be
damaged.
ADJUSTING THE REAR SHOCK
ABSORBER HIGH COMPRESSION
DAMPING FORCE
1. Adjust:
• High compression damping force
By turning the adjuster "1".• STANDARD POSITION:
This is the position which is back
by the specific number of turns
from the fully turned-in position.
(Which align the punch mark "a"
on the adjuster with the punch
mark "b" on the adjuster body.)
Do not force the adjuster past the
minimum or maximum extent of
adjustment. The adjuster may be
damaged.
CHECKING THE TIRE PRESSURE
1. Measure:
• Tire pressure
Out of specification
→Adjust.
• 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. Correct the tire posi-
tion.
CHECKING AND TIGHTENING THE
SPOKES
1. Inspect:
• Spokes "1"
Bend/damage
→Replace.
Loose spoke
→Retighten.
2. Tighten:
• Spokes
Be sure to retighten these spokes be-
fore and after break-in. After a prac-
tice or a race check spokes for
looseness.
CHECKING THE WHEELS
1. Inspect:
• Wheel runout
Elevate the wheel and turn it.
Abnormal runout
→ Replace.
2. Inspect:
• Bearing free play
Exist play
→Replace.
CHECKING AND ADJUSTING THE
STEERING HEAD
1. Elevate the front wheel by placing
a suitable stand under the engine.
2. Check:
• Steering stem
Grasp the bottom of the forks and
gently rock the fork assembly
back and forth.
Free play
→Adjust steering head. Standard position:
About 11 clicks out
* About 10 clicks out
* For EUROPE
Stiffer "a"
→Increase the high
compression damping force.
(Turn the adjuster "1" in.)
Softer "b"
→Decrease the high
compression damping force.
(Turn the adjuster "1" out.)
Extent of adjustment:
Maximum Minimum
Fully turned in
position2 turns out
(from maximum
position)
Standard position:
About 1-1/2 turns out
* About 2 turns out
* For EUROPE
Standard tire pressure:
100 kPa (1.0 kgf/cm
2,
15 psi)
Spokes:
3 Nm (0.3 m•kg, 2.2
ft•lb)

3-20
CHASSIS
3. Check:
• Steering smooth action
Turn the handlebar lock to lock.
Unsmooth action
→Adjust steer-
ing ring nut.
4. Adjust:
• Steering ring nut
Steering ring nut adjustment
steps:
a. Remove the number plate.
b. Remove the handlebar and upper
bracket.
c. Loosen the steering ring nut "1"
using the steering nut wrench "2".
d. Tighten the steering ring nut "3"
using steering nut wrench "4".
• Apply the lithium soap base grease
on the thread of the steering stem.
• Set the torque wrench to the steer-
ing nut wrench so that they form a
right angle.
e. Loosen the steering ring nut one
turn.
f. Retighten the steering ring nut us-
ing the steering nut wrench.
Avoid over-tightening.
g. Check the steering stem by turn-
ing it lock to lock. If there is any
binding, remove the steering stem
assembly and inspect the steer-
ing bearings.
h. Install the washer "5", upper
bracket "6", washer "7", steering
stem nut "8", handlebar "9", han-
dlebar upper holder "10" and
number plate "11".
• The handlebar upper holder should
be installed with the punched mark
"a" forward.
• Install the handlebar so that the
marks "b" are in place on both
sides.
• Install the handlebar so that the pro-
jection "c" of the handlebar upper
holder is positioned at the mark on
the handlebar as shown.
• Insert the end of the fuel breather
hose "12" into the hole in the steer-
ing stem.
First tighten the bolts on the front
side of the handlebar upper holder,
and then tighten the bolts on the
rear side.
Steering nut wrench:
YU-33975/90890-01403
Steering nut wrench:
YU-33975/90890-01403
Steering ring nut (initial
tightening):
38 Nm (3.8 m•kg, 27
ft•lb)
Steering ring nut (final
tightening):
7 Nm (0.7 m•kg, 5.1
ft•lb)
Steering stem nut:
145 Nm (14.5 m•kg, 105
ft•lb)
Handlebar upper holder:
28 Nm (2.8 m•kg, 20
ft•lb)
Pinch bolt (upper brack-
et):
21 Nm (2.1 m•kg, 15
ft•lb)
Number plate:
7 Nm (0.7 m•kg, 5.1
ft•lb)

5-28
STEERING
STEERING
REMOVING THE STEERING
Order Part name Q'ty Remarks
TIGHTENING STEPS:
• Tighten ring nut. 38 Nm (3.8 m•kg, 27 ft•lb)
• Loosen it one turn.
• Retighten it. 7 Nm (0.7 m•kg, 5.1 ft•lb)
Hold the machine by placing the suitable stand
under the engine.Refer to "HANDLING NOTE".
Number plateRefer to "SEAT, FUEL TANK AND SIDE
COVERS" section in the CHAPTER 4.
Handlebar Refer to "HANDLEBAR" section.
Front fender
1 Steering stem nut 1
2 Front fork 2 Refer to "FRONT FORK" section.
3 Upper bracket 1
4 Steering ring nut 1 Refer to removal section.
5 Lower bracket 1
6 Bearing race cover 1
7 Upper bearing 1
8 Lower bearing 1 Refer to removal section.

5-29
STEERING
9 Bearing race 2 Refer to removal section. Order Part name Q'ty Remarks

5-30
STEERING
HANDLING NOTE
Support the machine securely so
there is no danger of it falling over.
REMOVING THE STEERING RING
NUT
1. Remove:
• Steering ring nut "1"
Use the steering nut wrench "2".
Support the steering stem so that
it may not fall down.
REMOVING THE LOWER
BEARING
1. Remove:
• Lower bearing "1"
Use the floor chisel "2".
Take care not to damage the steer-
ing shaft thread.
REMOVING THE BEARING RACE
1. Remove:
• Bearing race "1"
Remove the bearing race using
long rod "2" and the hammer.
CHECKING THE STEERING STEM
1. Inspect:
• Steering stem "1"
Bend/damage
→Replace.CHECKING THE BEARING AND
BEARING RACE
1. Wash the bearings and bearing
races with a solvent.
2. Inspect:
•Bearing "1"
• Bearing race
Pitting/damage
→Replace bear-
ings and bearing races as a set.
Install the bearing in the bearing
races. Spin the bearings by hand.
If the bearings hang up or are not
smooth in their operation in the
bearing races, replace bearings
and bearing races as a set.
INSTALLING THE LOWER
BRACKET
1. Install:
• Lower bearing "1"
Apply the lithium soap base grease
on the dust seal lip and bearing inner
circumference.
2. Install:
• Bearing race
• Upper bearing "1"
• Bearing race cover "2"
Apply the lithium soap base grease
on the bearing and bearing race cov-
er lip.
3. Install:
• Lower bracket "1"
Apply the lithium soap base grease
on the bearing, the portion "a" and
thread of the steering stem.
4. Install:
• Steering ring nut "1"
Tighten the steering ring nut using
the steering nut wrench "2".
Refer to "CHECKING AND AD-
JUSTING THE STEERING
HEAD" section in the CHAPTER
3.
5. Check the steering stem by turn-
ing it lock to lock. If there is any
binding, remove the steering stem
assembly and inspect the steer-
ing bearings. Steering nut wrench:
YU-33975/90890-01403
Steering ring nut:
7 Nm (0.7 m•kg, 5.1 ft•
lb)

5-31
STEERING
6. Install:
• Washer "1"
7. Install:
• Front fork "1"
• Upper bracket "2"
• Temporarily tighten the pinch bolts
(lower bracket).
• Do not tighten the pinch bolts (up-
per bracket) yet.
8. Install:
• Washer "1"
• Steering stem nut "2"
9. After tightening the nut, check the
steering for smooth movement. If
not, adjust the steering by loosen-
ing the steering ring nut little by lit-
tle.
10. Adjust:
• Front fork top end "a"11. Tighten:
• Pinch bolt (upper bracket) "1"
• Pinch bolt (lower bracket) "2"
Tighten the lower bracket to speci-
fied torque. If torqued too much, it
may cause the front fork to mal-
function.
Steering stem nut:
145 Nm (14.5 m•kg, 105
ft•lb)
Front fork top end (stan-
dard) "a":
5 mm (0.20 in)
Pinch bolt (upper brack-
et):
21 Nm (2.1 m•kg, 15
ft•lb)
Pinch bolt (lower brack-
et):
21 Nm (2.1 m•kg, 15
ft•lb)