2008 YAMAHA YZ450F oil

5-25
HANDLEBAR
REMOVING THE BRAKE MASTER
CYLINDER
1. Remove:
• Brake master cylinder bracket "1"
• Brake master cylinder "2"
• Do not let the brake master cylin-
der hang on the brake hose.
• Keep the brake master cylinder
cap side horizontal to prevent air
from coming in.
REMOVING THE GRIP
1. Remove:
•Grip "1"
Blow in air between the handlebar or
tube guide and the grip. Then remove
the grip which has become loose.
CHECKING THE HANDLEBAR
1. Inspect:
• Handlebar "1"
Bends/cracks/damage
→Re-
place.
Do not attempt to straighten a bent
handlebar as this may dangerous-
ly weaken the handlebar.
INSTALLING THE HANDLEBAR
1. Install:
• Handlebar lower holder "1"
• Washer "2"
• Nut (handlebar lower holder) "3"
• Install the handlebar lower holder
with its side having the greater dis-tance "a" from the mounting bolt
center facing forward.
• Apply the lithium soap base grease
on the thread of the handlebar low-
er holder.
• Installing the handlebar lower hold-
er in the reverse direction allows the
front-to-rear offset amount of the
handlebar position to be changed.
• Do not tighten the nut yet.
2. Install:
• Handlebar "1"
• Handlebar upper holder "2"
• Bolt (handlebar upper holder) "3"
• 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.
• First tighten the bolts on the front
side of the handlebar upper holder,
and then tighten the bolts on the
rear side.
3. Tighten:
• Nut (handlebar lower holder) "1"
4. Install:
• Left grip "1"
Apply the adhesive to the handle-
bar "2".
• Before applying the adhesive, wipe
off grease or oil on the handlebar
surface "a" with a lacquer thinner.
• Install the left grip to the handlebar
so that the line "b" between the two
arrow marks faces straight upward.
Bolt (handlebar upper
holder):
28 Nm (2.8 m•kg, 20
ft•lb)
Nut (handlebar lower
holder):
34 Nm (3.4 m•kg, 24
ft•lb)

5-26
HANDLEBAR
5. Install:
• Right grip "1"
•Collar "2"
Apply the adhesive on the tube
guide "3".
• Before applying the adhesive, wipe
off grease or oil on the tube guide
surface "a" with a lacquer thinner.
• Install the grip to the tube guide so
that the grip match mark "b" and
tube guide slot "c" form the angle as
shown.
6. Install:
•Collar "1"
• Grip cap cover "2"
• Throttle grip "3"
Apply the lithium soap base grease
on the throttle grip sliding surface.
7. Install:
• Throttle cables "1"
To tube guide "2".
Apply the lithium soap base grease
on the throttle cable end and tube
guide cable winding portion.
8. Install:
• Throttle cable cap "1"
• Screw (throttle cable cap) "2"
After tightening the screws, check
that the throttle grip "3" moves
smoothly. If it does not, retighten
the bolts for adjustment.
9. Install:
• Grip cap cover "1"
• Cover (throttle cable cap) "2"
10. Install:
• Brake master cylinder "1"
• Brake master cylinder bracket "2"
• Bolt (brake master cylinder brack-
et) "3"
• Install the bracket so that the arrow
mark "a" faces upward.
• First tighten the bolt on the upper
side of the brake master cylinder
bracket, and then tighten the bolt on
the lower side.
11. Install:
• Engine stop switch "1"
• Clutch lever holder "2"
• Bolt (clutch lever holder) "3"
• Hot starter lever holder "4"
• Bolt (hot starter lever holder) "5"
• Clamp "6"
• The engine stop switch, clutch lever
holder and clamp should be in-
stalled according to the dimensions
shown.
• Pass the engine stop switch lead in
the middle of the clutch lever hold-
er.
12. Install:
• Clutch cable "1"
• Hot starter cable "2"
Apply the lithium soap base grease
on the clutch cable end and hot start-
er cable end.
Screw (throttle cable
cap):
4 Nm (0.4 m•kg, 2.9
ft•lb)
Bolt (brake master cylin-
der bracket):
9 Nm (0.9 m•kg, 6.5
ft•lb)
Bolt (clutch lever holder):
4 Nm (0.4 m•kg, 2.9
ft•lb)
Bolt (hot starter lever
holder):
4 Nm (0.4 m•kg, 2.9
ft•lb)

5-33
SWINGARM
DISASSEMBLING THE SWINGARM
Order Part name Q'ty Remarks
1 Cap 2 Refer to removal section.
2 Relay arm 1
3 Connecting rod 1
4 Collar 2
5 Oil seal 2
6 Thrust bearing 2
7 Bushing 2
8 Oil seal 8
9 Bearing 10 Refer to removal section.

5-34
SWINGARM
HANDLING NOTE
Support the machine securely so
there is no danger of it falling over.
REMOVING THE CAP
1. Remove:
• Left cap "1"
Remove with a slotted-head screw-
driver inserted under the mark "a" on
the left cap.
REMOVING THE BEARING
1. Remove:
• Bearing "1"
Remove the bearing by pressing its
outer race.
CHECKING THE SWINGARM
1. Inspect:
• Bearing "1"
• Bushing "2"
Free play exists/unsmooth revolu-
tion/rust
→Replace bearing and
bushing as a set.
2. Inspect:
• Oil seal "3"
Damage
→Replace.
CHECKING THE RELAY ARM
1. Inspect:
• Bearing "1"
•Collar "2"
Free play exists/unsmooth revolu-
tion/rust
→ Replace bearing and
collar as a set.2. Inspect:
• Oil seal "3"
Damage
→Replace.
CHECKING THE CONNECTING
ROD
1. Inspect:
•Bearing "1"
• Collar "2"
Free play exists/unsmooth revolu-
tion/rust
→Replace bearing and
collar as a set.
2. Inspect:
• Oil seal "3"
Damage
→Replace.
INSTALLING THE BEARING AND
OIL SEAL
1. Install:
•Bearing "1"
• Oil seal "2"
To swingarm.
• Apply the molybdenum disulfide
grease on the bearing when install-
ing.
• Install the bearing by pressing it on
the side having the manufacture's
marks or numbers.
• First install the outer and then the
inner bearings to a specified depth
from inside.
2. Install:
• Bearing "1"
• Washer "2"
• Oil seal "3"
To relay arm.
• Apply the molybdenum disulfide
grease on the bearing when install-
ing.
• Install the bearing by pressing it on
the side having the manufacture's
marks or numbers.
• Apply the molybdenum disulfide
grease on the washer.
3. Install:
• Bearing "1"
• Oil seal "2"
To connecting rod.
• Apply the molybdenum disulfide
grease on the bearing when install-
ing.
• Install the bearing by pressing it on
the side having the manufacture's
marks or numbers.
Installed depth of bear-
ings:
Outer "a": Zero mm
(Zero in)
Inner "b": 6.5 mm (0.26
in)
Installed depth of bear-
ings "a":
Zero mm (Zero in)
Installed depth of bear-
ings "a":
Zero mm (Zero in)

5-35
SWINGARM
INSTALLING THE SWINGARM
1. Install:
• Bushing "1"
• Thrust bearing "2"
• Oil seal "3"
•Collar "4"
To swingarm "5".
Apply the molybdenum disulfide
grease on the bushings, thrust bear-
ings, oil seal lips and contact surfaces
of the collar and thrust bearing.
2. Install:
•Collar "1"
• Washer "2"
To relay arm "3".
Apply the molybdenum disulfide
grease on the collars and oil seal lips.
3. Install:
•Collar "1"
To connecting rod "2".
Apply the molybdenum disulfide
grease on the collar and oil seal lips.
4. Install:
• Connecting rod "1"
• Bolt (connecting rod) "2"• Washer "3"
• Nut (connecting rod) "4"
To relay arm "5".
Apply the molybdenum disulfide
grease on the bolt.
5. Install:
• Relay arm "1"
• Bolt (relay arm) "2"
• Washer "3"
• Nut (relay arm) "4"
To swingarm.
• Apply the molybdenum disulfide
grease on the bolt circumference
and threaded portion.
• Do not tighten the nut yet.
6. Install:
• Swingarm "1"
• Pivot shaft "2"
• Apply the molybdenum disulfide
grease on the pivot shaft.
• Insert the pivot shaft from right side.
7. Check:
• Swingarm side play "a"
Free play exists
→Replace thrust
bearing.• Swingarm up and down move-
ment "b"
Unsmooth movement/binding/
rough spots
→Grease or replace
bearings, bushings and collars.
8. Install:
• Bolt (connecting rod) "1"
• Washer "2"
• Nut (connecting rod) "3"
• Apply the molybdenum disulfide
grease on the bolt.
• Do not tighten the nut yet.
9. Install:
• Bolt (rear shock absorber-relay
arm) "1"
• Nut (rear shock absorber-relay
arm) "2"
Apply the molybdenum disulfide
grease on the bolt.
10. Tighten:
• Nut (connecting rod) "1"
Nut (connecting rod):
80 Nm (8.0 m•kg, 58
ft•lb)
Pivot shaft:
85 Nm (8.5 m•kg, 61
ft•lb)
Nut (rear shock absorb-
er-relay arm):
53 Nm (5.3 m•kg, 38
ft•lb)
Nut (connecting rod):
80 Nm (8.0 m•kg, 58
ft•lb)

5-39
REAR SHOCK ABSORBER
HANDLING NOTE
• Support the machine securely so
there is no danger of it falling
over.
• This rear shock absorber is pro-
vided with a separate type tank
filled with high-pressure nitro-
gen gas. To prevent the danger
of explosion, read and under-
stand the following information
before handling the shock ab-
sorber. The manufacturer can
not be held responsible for prop-
erty damage or personal injury
that may result from improper
handling.
• Never tamper or attempt to dis-
assemble the cylinder or the
tank.
• Never throw the rear shock ab-
sorber into an open flame or
other high heat. The rear shock
absorber may explode as a re-
sult of nitrogen gas expansion
and/ or damage to the hose.
• Be careful not to damage any
part of the gas tank. A damaged
gas tank will impair the damp-
ing performance or cause a
malfunction.
• Take care not to scratch the
contact surface of the piston
rod with the cylinder; or oil
could leak out.
• Never attempt to remove the
plug at the bottom of the nitro-
gen gas tank. It is very danger-
ous to remove the plug.
• When scrapping the rear shock
absorber, follow the instruc-
tions on disposal.
NOTES ON DISPOSAL (YAMAHA
DEALERS ONLY)
Before disposing the rear shock ab-
sorber, be sure to extract the nitrogen
gas from valve "1". Wear eye protec-
tion to prevent eye damage from es-
caping gas and/or metal chips.
To dispose of a damaged or worn-
out rear shock absorber, take the
unit to your Yamaha dealer for this
disposal procedure.
REMOVING THE BEARING
1. Remove:
• Stopper ring (upper bearing) "1"
Press in the bearing while pressing its
outer race and remove the stopper
ring.
2. Remove:
• Upper bearing "1"
Remove the bearing by pressing its
outer race.
3. Remove:
• Lower bearing "1"
Remove the bearing by pressing its
outer race.
CHECKING THE REAR SHOCK
ABSORBER
1. Inspect:
• Damper rod "1"
Bends/damage
→Replace rear
shock absorber assembly.
• Shock absorber "2"
Oil leaks
→Replace rear shock
absorber assembly.
Gas leaks
→Replace rear shock
absorber assembly.• Spring "3"
Damage
→Replace spring.
Fatigue
→Replace spring.
Move spring up and down.
• Spring guide "4"
Wear/damage
→Replace spring
guide.
• Spring seat "5"
Cracks/damage
→Replace.
• Bearing "6"
Free play exists/unsmooth revolu-
tion/rust
→Replace.
INSTALLING THE BEARING
1. Install:
• Upper bearing "1"
Install the bearing parallel until the
stopper ring groove appears by
pressing its outer race.
Do not apply the grease on the
bearing outer race because it will
wear the rear shock absorber sur-
face on which the bearing is press
fitted.
2. Install:
• Stopper ring (upper bearing) "1"
After installing the stopper ring, push
back the bearing until it contacts the
stopper ring.

6-1
ELECTRICAL COMPONENTS AND WIRING DIAGRAM
ELECTRICAL
ELECTRICAL
COMPONENTS AND
WIRING DIAGRAM
ELECTRICAL COMPONENTS
1. Engine stop switch
2. Throttle position sensor
3. Neutral switch4. CDI magneto
5. Ignition coil
6. Spark plug7. CDI unit
WIRING DIAGRAM
1. Engine stop switch
2. Throttle position sensor
3. Neutral switch
4. CDI magneto
5. Ignition coil
6. Spark plug
7. CDI unitCOLOR CODE
BBlack
Br Brown
GGreen
LBlue
O Orange
PPink
RRed
Sb Sky blue
WWhiteY Yellow
B/L Black/Blue
B/W Black/White
B/Y Black/Yellow
G/B Green/Black
L/W Blue/White
R/W Red/White
B/WB/W
B/L
B/Y
SbSb
G/B
LYLY
P
B
B
B
B
G
O
WR
P
GW
R P
B Br W
W
B/Y GBr
G RR
OB Sb Sb Y
Y
WY
W
GG
B
PP
Br BrR R
OL
B SbY LL
B/L B/W B/WG/B
B B
B/L L Sb
B/L
G/B
G/BB/Y
B/Y
B/W
O B/W
BrBrP
6

6-2
IGNITION SYSTEM
IGNITION SYSTEM
INSPECTION STEPS
Use the following steps for checking the possibility of the malfunctioning engine being attributable to ignition system failure
and for checking the spark plug which will not spark.
*marked: Only when the ignition checker is used.
• Remove the following parts before inspection.
1. Seat
2. Fuel tank
• Use the following special tools in this inspection.
Spark gap test Spark→*Clean or replace spark plug.
No spark
↓
Check entire ignition system for connection.
(couplers, leads and ignition coil)No good→Repair or replace.
OK
↓
Check engine stop switch. No good→Replace.
OK
↓
Check ignition coil. (primary coil and secondary
coil)No good→Replace.
OK
↓
Check CDI magneto. (pickup coil and charging
coil)No good→Replace.
OK
↓
Check neutral switch. No good→Repair or replace.
OK
↓
Replace CDI unit.
Dynamic spark tester:
YM-34487
Ignition checker:
90890-06754
Pocket tester:
YU-3112-C/90890-03112