Valve YAMAHA YZ450F 2003 Service Manual

4 - 41
ENGVALVES AND VALVE SPRINGS
3. Install:
Valve cotters
NOTE:
While compressing the valve spring with a
valve spring compressor 1 install the valve
cotters.
4. To secure the valve cotters onto the
valve stem, lightly tap the valve tip with a
piece of wood.
CAUTION:
Hitting the valve tip with excessive force
could damage the valve.
Valve spring compressor:
YM-4019/90890-04019
5. Install:
Adjusting pad 1
Valve lifter 2
NOTE:
Apply the engine oil on the valve lifters.
Apply the molybdenum disulfide oil on the
valve stem end.
Valve lifter must turn smoothly when rotated
with a finger.
Be careful to reinstall valve lifters and pads
in their original place.

5 - 27
CHASFRONT FORK
EC558000
FRONT FORK DISASSEMBLY
Extent of removal:1 Oil seal removal2 Damper rod removal
Extent of removal Order Part name Q’ty Remarks
FRONT FORK DISASSEMBLY
1 Cap bolt 1 Refer to “REMOVAL POINTS”.
2 Fork spring 1 Drain the fork oil.
3 Dust seal 1
Refer to “REMOVAL POINTS”. 4 Stopper ring 1
5 Inner tube 1
6 Outer tube 1
7 Piston metal 1
8 Slide metal 1
9 Plain washer 1
0 Oil seal 1
A Spring guide 1
B Base valve 1 Use special tool.
C Damper rod 1 Refer to “REMOVAL POINTS”.
1
2

5 - 29
CHAS
EC553201
Inner tube
1. Remove:
Dust seal 1
Stopper ring 2
Using slotted-head screwdriver.
ACHTUNG:CAUTION:
Take care not to scratch the inner tube.
2. Remove:
Inner tube 1
Oil seal removal steps:
Push in slowly a the inner tube just before
it bottoms out and then pull it back quickly
b.
Repeat this step until the inner tube can
be pulled out from the outer tube.
EC553311
Damper rod
1. Remove:
Base valve 1
Damper rod 2
NOTE:
Use a damper rod holder 3 to lock the damper
rod.
EC554000
INSPECTION
EC554100
Damper rod
1. Inspect:
Damper rod 1
Bend/damage → Replace damper rod.
ACHTUNG:CAUTION:
The front fork with a built-in piston rod has
a very sophisticated internal construction
and is particularly sensitive to foreign
material.
Use enough care not to allow any foreign
material to come in when the oil is replaced
or when the front fork is disassembled and
reassembled.
Damper rod holder:
YM-1423/90890-01423
FRONT FORK

5 - 30
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 - 31
CHAS
EC554700
Cap bolt
1. Inspect:
Cap bolt 1
O-ring 2
Air bleed screw 3
Wear/damage → Replace.
FRONT FORK
EC555000
ASSEMBLY AND INSTALLATION
Front fork assembly
1. Wash the all parts in a clean solvent.
2. Install:
Damper rod 1
To inner tube 2.
ACHTUNG:CAUTION:
To install the damper rod into the inner
tube, hold the inner tube aslant. If the inner
tube is held vertically, the damper rod may
fall into it, damaging the valve inside.
3. Install:
Copper washer 1
O-ring 2
Base valve 3
To inner tube 4.
4. Tighten:
Base valve 1
NOTE:
Use a damper rod holder 2 to lock the
damper rod 3.
Apply the LOCTITE® on the base valve
thread.
Damper rod holder:
YM-1423/90890-01423
New
T R..55 Nm (5.5 m · kg, 40 ft · lb)

5 - 60
CHAS
EC586000
HANDLING NOTE
WARNING
This shock absorber is provided with a
separate type tank filled with high-pressure
nitrogen gas. To prevent the danger of
explosion, read and understand the follow-
ing information before handling the shock
absorber.
The manufacturer can not be held respon-
sible for property damage or personal
injury that may result from improper han-
dling.
1. Never tamper or attempt to disassem-
ble the cylinder or the tank.
2. Never throw the shock absorber into
an open flame or other high heat. The
shock absorber may explode as a
result of nitrogen gas expansion and/
or damage to the hose.
3. Be careful not to damage any part of
the gas tank. A damaged gas tank will
impair the damping performance or
cause a malfunction.
4. Take care not to scratch the contact
surface of the piston rod with the cylin-
der; or oil could leak out.
5. Never attempt to remove the plug at
the bottom of the nitrogen gas tank. It
is very dangerous to remove the plug.
6. When scrapping the shock absorber,
follow the instructions on disposal.
EC587000
NOTES ON DISPOSAL (YAMAHA DEALERS
ONLY)
Before disposing the shock absorber, be sure
to extract the nitrogen gas from valve 1. Wear
eye protection to prevent eye damage from
escaping gas and/or metal chips.
WARNING
To dispose of a damaged or worn-out
shock absorber, take the unit to your
Yamaha dealer for this disposal procedure.
REAR SHOCK ABSORBER

5 - 60
CHAS
HINWEIS ZUM UMGANG MIT DEM
STOSSDÄMPFER
WARNUNG
Der Stoßdämpfer enthält Stickstoff unter ho-
hem Druck. Vor Arbeiten am Stoßdämpfer die
folgenden Erläuterungen sorgfältig durchle-
sen und die gegebenen Vorsichtsmaßregeln
befolgen.
Der Hersteller übernimmt keinerlei Haftung für
Unfälle, Verletzungen oder Schäden, die auf
unsachgemäße Behandlung des Stoßdämp-
fers zurückzuführen sind.
1. Den Stoßdämpfer unter keinen Um-
ständen öffnen oder manipulieren.
2. Den Stoßdämpfer vor Hitze und offe-
nen Flammen schützen. Der hitzebe-
dingte Druckanstieg kann eine Explo-
sion des Stoßdämpfers bewirken.
3. Den Gaszylinder vor Verformung und
Beschädigung schützen. Ein defor-
mierter Zylinder vermindert die Dämpf-
wirkung.
4. Die Kontaktfläche zwischen Dämpfer-
rohr und Zylinder nicht zerkratzen, da
sonst Öl austreten kann.
5. UNTER KEINEN UMSTÄNDEN die
Schraube an der Unterseite des Gaszy-
linders lösen.
6. Den Stoßdämpfer sachgemäß entsor-
gen.
HINWEIS ZUR ENTSORGUNG
(nur Yamaha-Händler)
Vor der Entsorgung des Stoßdämpfers muß der
Gasdruck in dessen Innerem über das Ventil 1
vollständig abgebaut werden. Unbedingt eine
Schutzbrille tragen, um Augenverletzungen
durch ausströmendes Gas oder umherfliegen-
de Metallspäne zu vermeiden.
WARNUNG
Den Stoßdämpfer vom Yamaha-Händler
entsorgen lassen.
AMORTISSEUR ARRIERE
FEDERBEIN
REMARQUES CONCERNANT LA
MANIPULATION
AVERTISSEMENT
Cet amortisseur est muni d’un réservoir type
séparé contenant de l’azote sous haute pression.
Il doit être de ce fait manipulé avec une atten-
tion particulière. Afin d’éviter les risques
d’explosion, il convient de lire attentivement les
instructions suivantes.
Le fabricant de cet amortisseur ne peut être
tenu pour responsable de tout accident, dom-
mage matériel ou corporel résultant d’une
manipulation incorrecte.
1. Ne jamais essayer de démonter l’ensemble
cylindre ou le réservoir à gaz.
2. Ne jamais jeter un amortisseur usagé au
feu ou l’exposer à une chaleur intense.
L’amortisseur pourrait exploser suite à la
dilatation de l’azote qu’il contient ou à la
détérioration du flexible.
3. Prendre garde à ne pas endommager toute
partie du réservoir à gaz. Un réservoir à
gaz endommagé affectera la capacité
d’amortissement ou entraînera un mauvais
fonctionnement.
4. Prendre garde à ne pas rayer la surface de
contact de la tige du piston avec le cylindre;
l’huile pourrait fuir.
5. Ne jamais essayer d’enlever le plot situé au
bas du réservoir à azote, Il est très dange-
reux d’enlever le plot.
6. Pour la mise au rebut de l’amortisseur, sui-
vre les instructions concernant cette opéra-
tion.
REMARQUE CONCERNANT LA MISE AU
REBUT DE L’AMORTISSEUR (TRAVAIL A
EFFECTUER CHEZ UN
CONCESSIONNAIRE YAMAHA)
Avant de mettre l’amortisseur au rebut, ne pas
oublier d’extraire l’azote par la valve 1. Ne pas
oublier de porter des lunettes de protection pour se
protéger les yeux contre les copeaux métalliques et
le gaz qui s’échappe.
AVERTISSEMENT
Pour mettre au rebut un amortisseur endom-
magé ou usé, demander conseil à un concession-
naire Yamaha.

–+ELEC

6 - 2
MAP-CONTROLLED CDI UNIT
MAP-CONTROLLED CDI UNIT
A map-controlled, CDI ignition system is used in the YZ450F.
The microcomputer in the CDI unit detects the engine speed and throttle position, thus determining
the optimum ignition timing through the entire operating range. In this way, quick throttle response
can be achieved according to various riding conditions.
CDI unit
Throttle position sensor
Pickup coil CDI magneto rotorIgnition coil


Function of Component

Component Function
TPS
(throttle position sensor)Detects throttle valve opening and inputs it into the computer in the
CDI unit as a throttle opening signal.
Pickup coil Detects signal rotor revolutions and inputs them into the computer in
the CDI unit as engine revolution signals.
CDI unit The signals of the TPS and pickup coil sensor are analyzed by the
computer in the CDI unit, which then adjusts ignition timing for the
operation requirements.

Principal of 3-Dimensional Control
Conventionally, ignition timing was controlled only
by engine revolutions (2-dimensional control).
However, ignition timing needs advancement also
by engine load. Thus, accurate ignition timing can
be determined by adding throttle opening to deter-
mine ignition timing (3-dimensional control).
3-D Image Map of Ignition Timing
(different from actual characteristics)
Revolutions
Ignition timing
Throttle opening

7 - 3
TUN

SETTING
Effects of the setting parts on the throttle
valve opening
1
Pilot screw/pilot jet
2
Throttle valve cutaway
3
Jet needle
4
Main jet
ÅClosed
ıFully open
1/2 3/4 1/4 1/8
1
2
3
4
Åı
Main system
The FLATCR carburetor has a primary main
jet. This type of main jet is perfect for racing
motorcycles since it supplies an even flow of
fuel, even at full load. Use the main jet and the
jet needle to set the carburetor.

1
Jet needle
2
Pilot air jet
3
Needle jet
4
Main jet
5
Pilot jet
6
Pilot screw

7 - 9
TUN
Examples of carburetor setting depending on symptom
This should be taken simply for an example. It is necessary to set the carburetor while checking
the operating conditions of the engine.
Symptom Setting Checking
At full throttle
Hard breathing
Shearing noise
Whitish spark plug
Lean mixtureIncrease main jet calibration no.
(Gradually)Discoloration of spark plug →
If tan color, it is in good condition.
If cannot be corrected:
Clogged float valve seat
Clogged fuel hose
Clogged fuel cock
Check that the accelerator pump oper-
ates smoothly.
At full throttle
Speed pick-up stops
Slow speed pick-up
Slow response
Sooty spark plug
Rich mixtureDecrease main jet calibration no.
(Gradually)Discoloration of spark plug →
If tan color, it is in good condition.
If cannot be corrected:
Clogged air cleaner
Fuel overflow from carburetor
Lean mixture Lower jet needle clip position.
(1 groove down)
The clip position is the jet needle
groove on which the clip is installed.
The positions are numbered from the
top.
Check that the accelerator pump oper-
ates smoothly (except for rich mixture
symptom). Rich mixture Raise jet needle clip position.
(1 groove up)
1/4 ~ 3/4 throttle
Hard breathing
Lack of speedLower jet needle clip position.
(1 groove down)
1/4 ~ 1/2 throttle
Slow speed pick-up
Poor accelerationRaise jet needle clip position.
(1 groove up)
Closed to 1/4 throttle
Hard breathing
Speed downUse jet needle with a smaller diameter. Slow-speed-circuit passage
Clogged → Clean.
Overflow from carburetor
Closed to 1/4 throttle
Poor accelerationUse jet needle with a larger diameter.
Raise jet needle clip position. (1 groove
up)
Poor response in the low to
intermediate speedsRaise jet needle clip position.
If this has no effect, lower the jet needle
clip position.
Poor response when throttle
is opened quicklyCheck overall settings.
Use main jet with a lower calibration no.
Raise jet needle clip position.
(1 groove up)
If these have no effect, use a main jet
with a higher calibration no. and lower
the jet needle clip position.Check air cleaner for fouling.
Check that the accelerator pump oper-
ates smoothly.
Jet needleClip
Groobe 7 Groobe 6
Groobe 5
Groobe 4
Groobe 3
Groobe 2
Groobe 1
Leaner
↑
(Standard)
↓
Richer
*
SETTING