2008 YAMAHA YZ450F suspension

1-11
TORQUE-CHECK POINTS
TORQUE-CHECK POINTS
Concerning the tightening torque, refer to "TIGHTENING TORQUES" section in the CHAPTER 2.
Frame construction Frame to rear frame
Combined seat and fuel tank Fuel tank to frame
Exhaust system Silencer to rear frame
Engine mounting Frame to engine
Engine bracket to engine
Engine bracket to frame
Steering Steering stem to handlebar Steering stem to frame
Steering stem to upper bracket
Upper bracket to handlebar
Suspension Front Steering stem to front fork Front fork to upper bracket
Front fork to lower bracket
Rear For link type Assembly of links
Link to frame
Link to rear shock absorber
Link to swingarm
Installation of rear shock absorber Rear shock absorber to frame
Installation of swingarm Tightening of pivot shaft
Wheel Installation of wheel Front Tightening of wheel axle
Tightening of axle holder
Rear Tightening of wheel axle
Wheel to rear wheel sprocket
Brake Front Brake caliper to front fork
Brake disc to wheel
Tightening of union bolt
Brake master cylinder to handlebar
Tightening of bleed screw
Tightening of brake hose holder
Rear Brake pedal to frame
Brake disc to wheel
Tightening of union bolt
Brake master cylinder to frame
Tightening of bleed screw
Tightening of brake hose holder
Fuel system Fuel tank to fuel cock
Lubrication system Tightening of oil hose clamp

2-2
GENERAL SPECIFICATIONS
Fuel:
Type Premium unleaded gasoline only with a research octane
number of 95 or higher.
Tank capacity 7.0 L (1.54 Imp gal, 1.85 US gal)
Carburetor:
Type FCR-MX39
Manufacturer KEIHIN
Spark plug:
Type/manufacturer CR8E/NGK (resistance type)
Gap 0.7–0.8 mm (0.028–0.031 in)
Clutch type: Wet, multiple-disc
Transmission:
Primary reduction system Gear
Primary reduction ratio 61/23 (2.652)
Secondary reduction system Chain drive
Secondary reduction ratio 49/13 (3.769)
Transmission type Constant mesh, 5-speed
Operation Left foot operation
Gear ratio:
1st 27/14 (1.929)
2nd 23/15 (1.533)
3rd 23/18 (1.278)
4th 24/22 (1.091)
5th 20/21 (0.952)
Chassis: USA, CDN, AUS, NZ, ZA EUROPE
Frame type Semi double cradle
←
Caster angle 26.9° 26.7°
Trail 115.2 mm (4.54 in) 113.8 mm (4.48 in)
Tire:
Type With tube
Size (front) 80/100-21 51M
Size (rear) 120/80-19 63M (For USA, CDN, ZA, AUS, NZ)
110/90-19 62M (For EUROPE)
Tire pressure (front and rear) 100 kPa (1.0 kgf/cm
2, 15 psi)
Brake:
Front brake type Single disc brake
Operation Right hand operation
Rear brake type Single disc brake
Operation Right foot operation
Suspension:
Front suspension Telescopic fork
Rear suspension Swingarm (link type monocross suspension)
Shock absorber:
Front shock absorber Coil spring/oil damper
Rear shock absorber Coil spring/gas, oil damper

2-8
MAINTENANCE SPECIFICATIONS
CHASSISSide clearance 0.09–0.17 mm (0.0035–0.0067 in) 0.24 mm (0.009
in)
Housing and rotor clearance 0.03–0.10 mm (0.0012–0.0039 in) 0.17 mm (0.007
in)
Bypass valve setting pressure 40–80 kPa (0.4–0.8 kg/cm
2, 5.69–11.38
psi)----
Cooling:
Radiator core size
Width 120.2 mm (4.73 in) ----
Height 240 mm (9.45 in) ----
Thickness 22 mm (0.87 in) ----
Radiator cap opening pressure 110 kPa (1.1 kg/cm
2, 15.6 psi) ----
Radiator capacity (total) 0.56 L (0.49 Imp qt, 0.59 US qt) ----
Water pump
Type Single-suction centrifugal pump ----Item Standard Limit
Item Standard Limit
Steering system:
Steering bearing typeTaper roller bearing ----
Front suspension:
Front fork travel 300 mm (11.8 in) ----
Fork spring free length 454 mm (17.9 in) 449 mm (17.7
in)
Spring rate, STD K = 4.6 N/mm (0.469 kg/mm, 26.3 lb/in) ----
Optional spring Yes ----
Oil capacity 541 cm
3 (19.0 lmp oz, 18.3 US oz) ----
Oil grade Suspension oil "S1" ----
Inner tube outer diameter 48 mm (1.89 in) ----
Front fork top end 5 mm (0.20 in) ----
Rear suspension: USA, CDN, AUS, NZ,
ZAEUROPE
Shock absorber travel 131.5 mm (5.18 in)
←----
Spring free length Approx.275 mm (10.83
in)
←----
Fitting length
One I.D. mark 267 mm (10.51 in) 262 mm (10.31 in) ----
Two I.D. marks 273 mm (10.75 in) 268 mm (10.55 in) ----
Three I.D. marks 264.5 mm (10.41 in) 259.5 mm (10.22 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 rate, STD K = 54.0 N/mm (5.50 kg/
mm, 308.0 lb/in)
←----

3-3
MAINTENANCE INTERVALS
Lubricate pivot point●●
Check brake disc surface●●
Check fluid level and leakage●●
Retighten brake disc bolts, cali-
per bolts, master cylinder bolts
and union bolts●●
Replace pads●
Replace brake fluid●Every one year
FRONT FORKS
Inspect and adjust
●●
Replace oil●●Suspension oil "S1"
Replace oil seal
●
FRONT FORK OIL SEAL AND
DUST SEAL
Clean and lube
●●Lithium base grease
PROTECTOR GUIDE
Replace
●
REAR SHOCK ABSORBER
Inspect and adjust
●●
Lube●
(After
rain
ride)
●Molybdenum disulfide grease
Replace spring seat
●Every one year
Retighten
●●
DRIVE CHAIN GUIDE AND
ROLLERS
Inspect
●●
SWINGARM
Inspect, lube and retighten
●●Molybdenum disulfide grease
RELAY ARM, CONNECTING
ROD
Inspect, lube and retighten
●●Molybdenum disulfide grease
STEERING HEAD
Inspect free play and retighten
●●
Clean and lube●Lithium base grease
Replace bearing
●
TIRE, WHEELS
Inspect air pressure, wheel run-
out, tire wear and spoke loose-
ness
●●
Retighten sprocket bolt●●
Inspect bearings●
Replace bearings●
Lubricate●Lithium base grease ItemAfter
break-
inEvery
race
Every
third
(or 500
km)Every
fifth (or
1,000
km)
As re-
quiredRemarks

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.

5-22
FRONT FORK
If the adjuster is installed out of spec-
ification, proper damping force can-
not be obtained.
29. Tighten:
• Adjuster (locknut) "1"
Hold the locknut "2" and tighten the
adjuster with specified torque.
30. Install:
• Adjuster "1"
To inner tube.
31. Fill:
• Front fork oil "1"
From outer tube top.
Never fail to make the oil amount
adjustment between the maximum
and minimum amount and always adjust each front fork to the same
setting. Uneven adjustment can
cause poor handling and loss of
stability.
• 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.
32. Install:
• Damper assembly "1"
To outer tube.
Temporarily tighten the damper as-
sembly.
33. Install:
• Protector guide "1"
INSTALLING THE FRONT FORK
1. Install:
• Front fork "1"
• Temporarily tighten the pinch bolts
(lower bracket).
• Do not tighten the pinch bolts (up-
per bracket) yet.
2. Tighten:
• Damper assembly "1"
Use the cap bolt ring wrench "2" to
tighten the damper assembly with
specified torque.
3. Adjust:
• Front fork top end "a"
4. 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.
Adjuster (locknut):
29 Nm (2.9 m•kg, 21
ft•lb)
Adjuster:
55 Nm (5.5 m•kg, 40
ft•lb)
Recommended oil:
Suspension oil "S1"
Standard oil amount:
350 cm
3 (12.3 Imp oz,
11.8 US oz)
Extent of adjustment:
300–375 cm
3
(10.6–13.2 Imp oz,10.1–
12.7 US oz)
Damper assembly:
30 Nm (3.0 m•kg, 22
ft•lb)
Cap bolt ring wrench:
YM-01501/90890-01501
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)

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)

7-9
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).