length YAMAHA YZ450F 2008 User Guide

4-16
CAMSHAFTS
REMOVING THE CAMSHAFT
1. Remove:
• Timing mark accessing screw "1"
• Crankshaft end accessing screw
"2"
2. Align:
• T.D.C. mark
With align mark.
Checking steps:
a. Turn the crankshaft counterclock-
wise with a wrench.
b. Align the T.D.C. mark "a" on the
rotor with the align mark "b" on the
crankcase cover when piston is at
T.D.C. on compression stroke.
In order to be sure that the piston is at
Top Dead Center, the punch mark "c"
on the exhaust camshaft and the
punch mark "d" on the intake cam-
shaft must align with the cylinder
head surface, as shown in the illustra-
tion.
3. Remove:
• Timing chain tensioner cap bolt
"1"
• Timing chain tensioner "2"
• Gasket4. Remove:
• Bolt (camshaft cap) "1"
• Camshaft cap "2"
• Clip
Remove the bolts (camshaft cap) in a
crisscross pattern, working from the
outside in.
The bolts (camshaft cap) must be
removed evenly to prevent dam-
age to the cylinder head, cam-
shafts or camshaft caps.
5. Remove:
• Exhaust camshaft "1"
• Intake camshaft "2"
Attach a wire "3" to the timing chain to
prevent it from falling into the crank-
case.
CHECKING THE CAMSHAFT
1. Inspect:
• Cam lobe
Pitting/scratches/blue discolora-
tion
→Replace.
2. Measure:
• Cam lobe length "a" and "b"
Out of specification
→Replace.3. Measure:
• Runout (camshaft)
Out of specification
→Replace.
4. Measure:
• Camshaft-to-cap clearance
Out of specification
→Measure
camshaft outside diameter.
Cam lobes length:
Intake "a":
31.200–31.300 mm
(1.2283–1.2323 in)
:
31.100 mm (1.2244 in)
Intake "b":
22.550–22.650 mm
(0.8878–0.8917 in)
:
22.450 mm (0.8839 in)
Exhaust "a":
30.900–31.000 mm
(1.2165–1.2205 in)
:
30.800 mm (1.2126 in)
Exhaust "b":
22.468–22.568 mm
(0.8846–0.8885 in)
:
22.368 mm (0.8806 in)
Runout (camshaft):
Less than 0.03 mm
(0.0012 in)

4-25
VALVES AND VALVE SPRINGS
CHECKING THE VALVE SPRINGS
1. Measure:
• Valve spring free length "a"
Out of specification
→Replace.
2. Measure:
• Compressed spring force "a"
Out of specification
→Replace.
b. Installed length
3. Measure:
• Spring tilt "a"
Out of specification
→Replace.CHECKING THE VALVE LIFTERS
1. Inspect:
• Valve lifter
Scratches/damage
→Replace
both lifters and cylinder head.
INSTALLING THE VALVES
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"
• Make sure that each valve is in-
stalled in its original place, also re-
ferring to the painted color as
follows.
Intake (middle) "a": blue
Intake (right/left) "b": gray
Exhaust "c": brown
• Install the valve springs with the
larger pitch "d" facing upward.
e. Smaller pitch3. Install:
• Valve cotters
While compressing the valve spring
with a valve spring compressor "1" in-
stall the valve cotters.
4. To secure the valve cotters onto
the valve stem, lightly tap the
valve tip with a piece of wood.
Hitting the valve tip with excessive
force could damage the valve.
5. Install:
• Adjusting pad "1"
• Valve lifter "2"
• Apply the molybdenum disulfide oil
on the valve stem end.
• Apply the engine oil on the valve lift-
ers.
• Valve lifter must turn smoothly
when rotated with a finger.
• Be careful to reinstall valve lifters
and pads in their original place.
Free length (valve
spring):
Intake:
37.03 mm (1.46 in)
: 36.03 mm
(1.42 in)
Exhaust:
37.68 mm (1.48 in)
: 36.68 mm
(1.44 in)
Compressed spring
force:
Intake:
111.3–127.9 N at 27.87
mm (11.3–13.0 kg at
27.87 mm, 24.91–
28.66 lb at 1.10 in)
Exhaust:
127.4–146.4 N at 27.38
mm (13.0–14.9 kg at
27.38 mm, 28.66–
32.85 lb at 1.08 in)
Spring tilt limit:
Intake:
2.5°/1.61 mm (0.063
in)
Exhaust:
2.5°/1.65 mm (0.065
in)
Valve spring compres-
sor:
YM-4019/90890-04019

4-31
CLUTCH
REMOVING THE CLUTCH BOSS
1. Remove:
•Nut "1"
• Lock washer "2"
• Clutch boss "3"
Straighten the lock washer tab and
use the clutch holding tool "4" to hold
the clutch boss.
A. For USA and CDN
B. Except for USA and CDN
CHECKING THE CLUTCH
HOUSING AND BOSS
1. Inspect:
• Clutch housing "1"
Cracks/wear/damage
→Replace.
• Clutch boss "2"
Scoring/wear/damage
→Re-
place.
CHECKING THE PRIMARY DRIVEN
GEAR
1. Check:
• Circumferential play
Free play exists
→Replace.
• Gear teeth "a"
Wear/damage
→Replace.CHECKING THE CLUTCH
SPRINGS
1. Measure:
• Clutch spring free length "a"
Out of specification
→Replace
springs as a set.
CHECKING THE FRICTION
PLATES
1. Measure:
• Friction plate thickness
Out of specification
→Replace
friction plate as a set.
Measure at all four points.
CHECKING THE CLUTCH PLATES
1. Measure:
• Clutch plate warpage
Out of specification
→Replace
clutch plate as a set.
Use a surface plate "1" and thick-
ness gauge "2".
CHECKING THE PUSH LEVER
SHAFT
1. Inspect:
• Push lever shaft "1"Wear/damage
→Replace.
CHECKING THE PUSH ROD
1. Inspect:
• Push rod 1 "1"
• Bearing "2"
• Washer "3"
• Push rod 2 "4"
•Ball "5"
Wear/damage/bend
→Replace.
INSTALLING THE PUSH LEVER
SHAFT
1. Install:
• Push lever shaft "1"
• Apply the lithium soap base grease
on the oil seal lip.
• Apply the engine oil on the push le-
ver shaft.
INSTALLING THE CLUTCH
1. Install:
• Primary driven gear "1"
• Thrust washer "2"
• Clutch boss "3"
Apply the engine oil on the primary
driven gear inner circumference.
2. Install:
• Lock washer "1" Clutch holding tool:
YM-91042/90890-04086
Clutch spring free
length:
50.0 mm (1.97 in)
: 49.0 mm (1.93
in)
Friction plate thickness:
2.92–3.08 mm (0.115–
0.121 in)
: 2.8 mm (0.110
in)
Warp limit:
0.1 mm (0.004 in)

5-19
FRONT FORK
Contamination →Clean.
• O-ring "2"
Wear/damage
→Replace.
• Piston metal "3"
Wear/damage
→Replace.
• Spring "4"
Damage/fatigue
→Replace base
valve.
• Air bleed screw "5"
Wear/damage
→Replace.
CHECKING THE COLLAR
1. Inspect:
• Piston metal "1"
Wear/damage
→Replace.
CHECKING THE FORK SPRING
1. Measure:
• Fork spring free length "a"
Out of specification
→Replace.
CHECKING THE INNER TUBE
1. Inspect:
• Inner tube surface "a"
Score marks
→Repair or replace.
Use #1,000 grit wet sandpaper.
Damaged oil lock piece
→Re-
place.
• Inner tube bends
Out of specification
→Replace.
Use the dial gauge "1".
The bending value is shown by one half of the dial gauge reading.
Do not attempt to straighten a bent
inner tube as this may dangerous-
ly weaken the tube.
CHECKING THE OUTER TUBE
1. Inspect:
• Outer tube "1"
Score marks/wear/damage
→Re-
place.
CHECKING THE ADJUSTER
1. Inspect:
•Adjuster "1"
• O-ring "2"
Wear/damage
→Replace.
ASSEMBLING THE FRONT FORK
1. Wash the all parts in a clean sol-
vent.
2. Stretch the damper assembly ful-
ly.
3. Fill:
• Front fork oil "1"
To damper assembly.
• Be sure to use recommended
fork oil. If other oils are used,
they may have an excessively ad-
verse effect on the front fork per-
formance.
• Never allow foreign materials to enter the front fork.
4. After filling, pump the damper as-
sembly "1" slowly up and down
(about 200 mm (7.9 in) stroke)
several times to bleed the damper
assembly of air.
Be careful not to excessive full stroke.
A stroke of 200 mm (7.9 in) or more
will cause air to enter. In this case, re-
peat the steps 2 to 4.
5. Measure:
• Oil level (left and right) "a"
Out of specification
→ Adjust.
6. Tighten:
• Locknut "1"
Fully finger tighten the locknut onto
the damper assembly.
Fork spring free length:
454 mm (17.9 in)
: 449 mm (17.7
in)
Inner tube bending limit:
0.2 mm (0.008 in)
Recommended oil:
Suspension oil "S1"
Oil capacity:
199 cm
3 (7.00 Imp oz,
6.73 US oz)
Standard oil level:
145-148 mm (5.71-5.83
in)
From top of fully
stretched damper as-
sembly.

5-40
REAR SHOCK ABSORBER
3. Install:
• Lower bearing "1"
Install the bearing by pressing it on
the side having the manufacture's
marks or numbers.
INSTALLING THE SPRING (REAR
SHOCK ABSORBER)
1. Install:
• Spring "1"
• Upper spring guide "2"
• Lower spring guide "3"
2. Install:
• Spring seat "1"
Install the spring seat with the projec-
tion "a" brought into contact with the
spring end, as shown.
3. Tighten:
•Adjuster "1"
4. Adjust:
• Spring length (installed)
Refer to "ADJUSTING THE
REAR SHOCK ABSORBER
SPRING PRELOAD" section in
the CHAPTER 3.
5. Tighten:
• Locknut "1"
INSTALLING THE REAR SHOCK
ABSORBER
1. Install:
• Dust seal "1"
• O-ring "2"
• Collar "3"
• Apply the molybdenum disulfide
grease on the dust seal lips and col-
lars.
• Apply the lithium soap base grease
on the O-rings.
2. Install:
• Bushing "1"
• Collar "2"
• Dust seal "3"
• Apply the molybdenum disulfide
grease on the bearing and dust seal
lips.
• Install the dust seals with their lips
facing outward.
3. Install:
• Rear shock absorber
4. Install:
• Bolt (rear shock absorber-frame)
"1"
• Washer "2"
• Nut (rear shock absorber-frame)
"3"
Apply the molybdenum disulfide
grease on the bolt.
5. Install:
• Bolt (rear shock absorber-relay
arm) "1"
• Nut (rear shock absorber-relay
arm) "2"
Apply the molybdenum disulfide
grease on the bolt.
6. Install:
• Rear frame "1"
• Bolt [rear frame (upper)] "2" Installed depth of the
bearing "a":
4 mm (0.16 in)
Nut (rear shock absorb-
er-frame):
56 Nm (5.6 m•kg, 40
ft•lb)
Nut (rear shock absorb-
er-relay arm):
53 Nm (5.3 m•kg, 38
ft•lb)
Bolt [rear frame (upper)]:
38 Nm (3.8 m•kg, 27
ft•lb)

7-7
CHASSIS
C. Stroke
1. Max. oil amount
2. Standard oil amount
3. Min. oil amount
SETTING OF SPRING AFTER
REPLACEMENT
As the front fork setting can be easily
affected by rear suspension, take
care so that the machine front and
rear are balanced (in position, etc.)
when setting the front fork.
1. Use of soft spring
• Change the rebound damping.
Turn out one or two clicks.
• Change the compression damp-
ing.
Turn in one or two clicks.
Generally a soft spring gives a soft
riding feeling. Rebound damping
tends to become stronger and the
front fork may sink deeply over a se-
ries of gaps.
2. Use of stiff spring
• Change the rebound damping.
Turn in one or two clicks.
• Change the compression damp-
ing.
Turn out one or two clicks.
Generally a stiff spring gives a stiff
riding feeling. Rebound damping
tends to become weaker, resulting in
lack of a sense of contact with the
road surface or in a vibrating handle-
bar.
FRONT FORK SETTING PARTS
• Front fork spring "1"
The I.D. mark (slits) "a" is proved on the end of the spring.
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 following 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 damp-
ing.
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 adjustment by turning the spring
adjuster "2" to achieve the stan-
dard figure from the subtraction of
the length "b" from the length "a".
• 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 reeval-
uation.
• 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 readjust-
ment.
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 re-
bound 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 re-
bound damping to compensate
for its greater spring load. Run
with the rebound damping adjust-
er 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 cor-
rection, turn the low compression
damping adjuster on the softer side.
When using a rear shock absorber
other than currently installed, use
the one whose overall length "a" TY
PESPRIN
G
RATESPRING PART
NUMBERI.D.
MA
RK
(slit
s)
SO
FT0.398 1C3-23141-A1 |
0.408 1C3-23141-B1 ||
0.418 1C3-23141-C1 |||
0.428 1C3-23141-D1 ||||
0.438 1C3-23141-E1 |||||
0.449 1C3-23141-F1 |-|
0.459 1C3-23141-G1 |-||
ST
D0.469 2S2-23141-L1 —
STI
FF0.479 1C3-23141-J1 |-||||
Standard figure:
90–100 mm (3.5–3.9 in)

7-8
CHASSIS
does not exceed the standard as it
may result in faulty performance.
Never use one whose overall
length is greater than standard.
REAR SHOCK ABSORBER
SETTING PARTS
• Rear shock spring "1"
[Equal-pitch titanium spring]
[Equal-pitch steel spring][Unequal-pitch steel spring]
Install the spring seat "2" to the ti-
tanium spring.
• The unequal-pitch spring is softer in
initial characteristic than the equal-
pitch spring and is difficult to bottom
out under full compression.
• The I.D. mark "a" is marked at the
end of the spring.
• Spring specification varies accord-
ing to the color and quantity of I.D.
marks.
• Extent of adjustment (spring length)[Titanium spring]
[Steel spring] Length "a" of standard
shock:
490 mm (19.29 in)
T
Y
P
ESPRI
NG
RAT
ESPRING
PART
NUM-
B E R
(-22212-)I.D.
MARKSPR
ING
FRE
E
LEN
GTH
(ap-
prox
.)
S
O
F
T4.5 1C3-00 Green 265
4.7 1C3-10 Red 265
4.9 1C3-20 Black 265
5.1 1C3-30 Blue 265
5.3 1C3-40 Yellow 275
S
T
D5.51C3-50
(1C3-B0)Pink 275
S
TI
F
F
5.71C3-60White275
T
Y
P
ESPRI
NG
RAT
ESPRING
PART
NUM-
BER
(-22212-)I.D.
MARK/
Q'TYSPR
ING
FRE
E
LEN
GTH
4.3 5UN-00 Brown/1 260
T
Y
P
ESPRI
NG
RAT
E
(ap-
prox.
)SPRING
PART
NUM-
B E R
(-22212-)I.D.
MARK/
Q'TYSPR
ING
FRE
E
LEN
GTH
S
O
F
T4.5 5UN-A0 Green/2 275
4.7 5UN-B0 Red/2 275
4.9 5UN-C0 Black/2 275
5.1 5UN-D0 Blue/2 275
5.3 5UN-E0Yellow/
2275
5.5 5UN-F0 Pink/2 275
S
TI
F
F5.7 5UN-G0 White/2 275
SPRING
FREE
LENGTHEXTENT OF AD-
JUSTMENT "b"
Approx.
265 mm
(10.43 in)One I.D. mark
245.5–263.5 mm
(9.67–10.37 in)
Two I.D. marks
251.5–269.5 mm
(9.90–10.61 in)
Three I.D. marks
243.0–261.0 mm
(9.57–10.28 in)
Approx.
275 mm
(10.83 in)One I.D. mark
255.5–273.5 mm
(10.06–10.77 in)
Two I.D. marks
261.5–279.5 mm
(10.30–11.00 in)
Three I.D. marks
253.0–271.0 mm
(9.96–10.67 in)
SPRING
FREE
LENGTHEXTENT OF AD-
JUSTMENT "b"
260 mm
(10.24 in)240.5–258.5 mm
(9.47–10.18 in)
275 mm
(10.83 in)255.5–273.5 mm
(10.06–10.77 in)

7-9
CHASSIS
SUSPENSION SETTING (FRONT FORK)
• 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
gapMedi-
um
gapSmall
gap
Stiff over entire
range
○○○
Compression damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Oil amount Decrease oil amount by about 5–10 cm
3 (0.2–0.4
Imp oz, 0.2–0.3 US oz).
Spring Replace with soft spring.
Unsmooth move-
ment over entire
range
○○○○
Outer tube Check for any bends, dents, and other noticeable
scars, etc. If any, replace affected parts.
Inner tube
Slide metal Replace with a new one for extended use.
Piston metal Replace with a new one for extended use.
Under bracket tighten-
ing torqueRetighten to specified torque.
Poor initial move-
ment
○
Rebound damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Oil seal Apply grease in oil seal wall.
Soft over entire
range, bottoming
out
○○
Compression damping Turn adjuster clockwise (about 2 clicks) to in-
crease damping.
Oil amount Increase oil amount by about 5–10 cm
3 (0.2–0.4
Imp oz, 0.2–0.3 US oz).
Spring Replace with stiff spring.
Stiff toward stroke
end
○Oil amountDecrease oil amount by about 5 cm3 (0.2 Imp
oz,0.2 US oz).
Soft toward stroke
end, bottoming out
○Oil amountIncrease oil amount by about 5 cm3 (0.2 Imp
oz,0.2 US oz).
Stiff initial move-
ment
○○○○Compression dampingTurn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Low front, tending to
lower front posture
○○
Compression damping Turn adjuster clockwise (about 2 clicks) to in-
crease damping.
Rebound damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Balance with rear end Set sunken length for 95–100 mm (3.7–3.9 in)
when one passenger is astride seat (lower rear
posture).
Oil amount Increase oil amount by about 5 cm
3 (0.2 Imp oz,
0.2 US oz).
"Obtrusive" front,
tending to upper
front posture
○○
Compression damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Balance with rear end Set sunken length for 90–95 mm (3.5–3.7 in)
when one passenger is astride seat (upper rear
posture).
Spring Replace with soft spring.
Oil amount Decrease oil amount by about 5–10 cm
3 (0.2–0.4
Imp oz, 0.2–0.3 US oz).

7-10
CHASSIS
SUSPENSION SETTING (REAR SHOCK ABSORBER)
• 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.
• Adjust the rebound damping in 2-click increments or decrements.
• Adjust the low compression damping in 1-click increments or decrements.
• Adjust the high compression damping in 1/6 turn increments or decrements.
SymptomSection
Check Adjust
JumpLarge
gapMedi-
um
gapSmall
gap
Stiff, tending to sink
○○
Rebound damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Spring set length Set sunken length for 90–100 mm (3.5–3.9 in)
when one passenger is astride seat.
Spongy and unsta-
ble
○○
Rebound damping Turn adjuster clockwise (about 2 clicks) to in-
crease damping.
Low compression
dampingTurn adjuster clockwise (about 1 click) to increase
damping.
Spring Replace with stiff spring.
Heavy and dragging
○○
Rebound damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Spring Replace with soft spring.
Poor road gripping
○
Rebound damping Turn adjuster counterclockwise (about 2 clicks) to
decrease damping.
Low compression
dampingTurn adjuster clockwise (about 1 clicks) to in-
crease damping.
High compression
dampingTurn adjuster clockwise (about 1/6 turn) to in-
crease damping.
Spring set length Set sunken length for 90–100 mm (3.5–3.9 in)
when one passenger is astride seat.
Spring Replace with soft spring.
Bottoming out
○○
High compression
dampingTurn adjuster clockwise (about 1/6 turn) to in-
crease damping.
Spring set length Set sunken length for 90–100 mm (3.5–3.9 in)
when one passenger is astride seat.
Spring Replace with stiff spring.
Bouncing
○○
Rebound damping Turn adjuster clockwise (about 2 clicks) to in-
crease damping.
Spring Replace with soft spring.
Stiff travel
○○
High compression
dampingTurn adjuster counterclockwise (about 1/6 turn) to
decrease damping.
Spring set length Set sunken length for 90–100 mm (3.5–3.9 in)
when one passenger is astride seat.
Spring Replace with soft spring.