engine YAMAHA YZ450F 2003 User Guide

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GEN
INFO

MACHINE IDENTIFICATION
EC120001
MACHINE IDENTIFICATION
There are two significant reasons for knowing
the serial number of your machine:
1. When ordering parts, you can give the
number to your Yamaha dealer for posi-
tive identification of the model you own.
2. If your machine is stolen, the authorities
will need the number to search for and
identify your machine.
EC121001
VEHICLE IDENTIFICATION NUMBER
The vehicle identification number
1
is
stamped on the right of the steering head pipe.
EC123001
ENGINE SERIAL NUMBER
The engine serial number
1
is stamped into
the elevated part of the right-side of the
engine.
EC124000
MODEL LABEL
The model label
1
is affixed to the frame
under the rider’s seat. This information will be
needed to order spare parts.

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GEN
INFO

IMPORTANT INFORMATION
EC132000
ALL REPLACEMENT PARTS
1. We recommend to use Yamaha genuine
parts for all replacements. Use oil and/or
grease recommended by Yamaha for
assembly and adjustment.
EC133000
GASKETS, OIL SEALS AND O-RINGS
1. All gaskets, oil seals, and O-rings should
be replaced when an engine is over-
hauled. All gasket surfaces, oil seal lips,
and O-rings must be cleaned.
2. Properly oil all mating parts and bearings
during reassembly. Apply grease to the
oil seal lips.
EC134000
LOCK WASHERS/PLATES AND COTTER
PINS
1. All lock washers/plates
1
and cotter pins
must be replaced when they are
removed. Lock tab(s) should be bent
along the bolt or nut flat(s) after the bolt
or nut has been properly tightened.
EC135001
BEARINGS AND OIL SEALS
1. Install the bearing(s)
1
and oil seal(s)
2
with their manufacturer’s marks or num-
bers facing outward. (In other words, the
stamped letters must be on the side
exposed to view.) When installing oil
seal(s), apply a light coating of light-
weight lithium base grease to the seal
lip(s). Oil the bearings liberally when
installing.
CAUTION:

Do not use compressed air to spin the
bearings dry. This causes damage to the
bearing surfaces.

GEN
INFO
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SPECIAL TOOLS
YU-33975, 90890-01403 Ring nut wrench
This tool is used when tighten the steering ring nut to
specification.YU-33975 90890-01403
YM-1423, 90890-01423 Damper rod holder
Use this tool to remove and install the damper rod.YM-1423 90890-01423
YM-01442, 90890-01442 Fork seal driver
This tool is used when install the fork oil seal.YM-01442 90890-01442
YU-3112-C, 90890-03112 Yamaha pocket tester
Use this tool to inspect the coil resistance, output
voltage and amperage.YU-3112-C 90890-03112
YU-8036-B
90890-03113Inductive tachometer
Engine tachometer
This tool is needed for observing engine rpm.YU-8036-B 90890-03113
YM-33277-A, 90890-03141 Timing light
This tool is necessary for checking ignition timing.YM-33277-A 90890-03141
YM-4019, 90890-04019 Valve spring compressor
This tool is needed to remove and install the valve
assemblies.YM-4019 90890-04019
YM-91042, 90890-04086 Clutch holding tool
This tool is used to hold the clutch when removing or
installing the clutch boss securing nut.YM-91042 90890-04086
YM-4116, 90890-04116
YM-4097, 90890-04097Valve guide remover
Intake 4.5 mm (0.18 in)
Exhaust 5.0 mm (0.20 in)
This tool is needed to remove and install the valve
guide.YM-4116
YM-409790890-04116
90890-04097
Part number Tool name/How to use Illustration

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GEN
INFO
CONTROL FUNCTIONS
EC150000
CONTROL FUNCTIONS
EC151000
“ENGINE STOP” BUTTON
The “ENGINE STOP” button 1 is located on
the left handlebar. Continue pushing the
“ENGINE STOP” button till the engine comes
to a stop.
EC152000
CLUTCH LEVER
The clutch lever 1 is located on the left han-
dlebar; it disengages or engages the clutch.
Pull the clutch lever to the handlebar to disen-
gage the clutch, and release the lever to
engage the clutch. The lever should be pulled
rapidly and released slowly for smooth starts.
EC153000
SHIFT PEDAL
The gear ratios of the constant-mesh 4 speed
transmission are ideally spaced. The gears
can be shifted by using the shift pedal 1 on
the left side of the engine.
EC154000
KICK STARTER
Rotate the kick starter 1 away from the
engine. Push the starter down lightly with your
foot until the gears engage, then kick smoothly
and forcefully to start the engine. This model
has a primary kick starter so the engine can be
started in any gear if the clutch is disengaged.
In normal practices, however, shift to neutral
before starting.
1
EC155001
THROTTLE GRIP
The throttle grip 1 is located on the right han-
dlebar; it accelerates or decelerates the
engine. For acceleration, turn the grip toward
you; for deceleration, turn it away from you.

GEN
INFOFONCTIONS DES COMMANDES
ARMATUREN UND DEREN FUNKTION
ARMATUREN UND DEREN FUNK-
TION
MOTORSTOPPSCHALTER “ENGINE STOP”
Der Motorstoppschalter “ENGINE STOP” 1
befindet sich auf der linken Seite des Lenkers.
Den Motorstoppschalter “ENGINE STOP” ge-
drückt halten, bis der Motor abstirbt.
KUPPLUNGSHEBEL
Der Kupplungshebel 1 befindet sich auf der lin-
ken Seite des Lenkers und dient zum Ein- und
Auskuppeln. Zum Ausrücken der Kupplung den
Kupplungshebel zum Lenkgriff ziehen; zum Ein-
rücken der Kupplung den Kupplungshebel wieder
freigeben. Zum Auskuppeln den Kupplungshebel
zügig ziehen, beim Einkuppeln gefühlvoll loslas-
sen, um ein weiches Einrücken der Kupplung zu
gewährleisten.
FUSSSCHALTHEBEL
Erst das Getriebe erlaubt die Nutzung der Mo-
torleistung in verschiedenen Geschwindig-
keitsbereichen, so daß Anfahren, Bergauffah-
ren und schnelles Beschleunigen möglich
sind. Die Gänge dieses 4-Gang-Getriebes
werden über den Fußschalthebel 1 linksseitig
des Motors bei ausgerückter Kupplung ge-
schaltet.
KICKSTARTER
Zum Anlassen des Motors den Kickstarterhebel
1 ausschwenken und langsam niedertreten,
bis deutlicher Widerstand spürbar wird; dann
den Kickstarterhebel schwungvoll durchtreten.
Dieses Modell ist mit einem Primärkickstarter
ausgerüstet, d. h. der Motor kann auch bei ein-
gelegtem Gang angelassen werden – voraus-
gesetzt, daß die Kupplung ausgerückt ist. Nor-
malerweise sollte jedoch in den Leerlauf
geschaltet werden, bevor der Motor gestartet
wird.
GASDREHGRIFF
Der Gasdrehgriff 1 befindet sich auf der rech-
ten Seite des Lenkers. Zum Erhöhen der Mo-
tordrehzahl (Beschleunigung) den Gasdreh-
griff in Gegenfahrtrichtung drehen, zum
Reduzieren der Motordrehzahl den Gasdreh-
griff in Fahrtrichtung drehen.
FONCTIONS DES COMMANDES
BOUTON D’ARRET DE MOTEUR “ENGINE
STOP”
Ce bouton d’arrêt de moteur “ENGINE STOP” 1
est situé sur le guidon gauche. Continuer à appuyer
sur le bouton d’arrêt de moteur “ENGINE STOP”
jusqu’a que ce le moteur s’arrête.
LEVIER D’EMBRAYAGE
Le levier d’embrayage 1 est situé sur le guidon
gauche et permet d’embrayer ou de débrayer. Tirer
le levier d’embrayage vers le guidon pour débrayer
et relâcher le levier pour embrayer. Pour des
démarrages doux, le levier doit être tiré rapidement
et relâché lentement.
PEDALE DE CHANGEMENT DE VITESSE
Les 4 rapports de la boîte de vitesses à prise cons-
tante sont idéalement échelonnés. Le changement
de vitesse est commandé par le sélecteur à pédale
1 situé du côté gauche du moteur.
DEMARREUR AU PIED
Déployer la pédale de démarreur au pied 1.
Appuyer légèrement sur la pédale jusqu’à ce que
les pignons se mettent en prise puis l’actionner
vigoureusement pour démarrer le moteur. Ce
modèle est muni d’un démarreur au pied primaire,
de sorte qu’on peut démarrer sur n’importe quelle
vitesse à condition de débrayer. Toutefois, norma-
lement, on remettra les vitesses au point mort avant
la mise en marche.
POIGNEE DES GAZ
La poignée des gaz 1 est située sur le guidon droit;
elle permet d’accélérer ou de décélérer le moteur.
Pour une accélération, tourner la poignée vers soi;
pour une décélération, la tourner de l’autre côté.
1 - 10

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GEN
INFO
CONTROL FUNCTIONS
EC156000
FRONT BRAKE LEVER
The front brake lever 1 is located on the right
handlebar. Pull it toward the handlebar to acti-
vate the front brake.
EC157000
REAR BRAKE PEDAL
The rear brake pedal 1 is located on the right
side of the machine. Press down on the brake
pedal to activate the rear brake.
EC158001
FUEL COCK
The fuel cock supplies fuel from the tank to
carburetor while filtering the fuel. The fuel cock
has the two positions:
OFF:With the lever in this position, fuel will not
flow. Always return the lever to this posi-
tion when the engine is not running.
ON: With the lever in this position, fuel flows
to the carburetor. Normal riding is done
with the lever in this position.
COLD STARTER KNOB
When cold, the engine requires a richer air-fuel
mixture for starting. A separate starter circuit,
which is controlled by the cold starter knob 1,
supplies this mixture. Pull the cold starter knob
out to open the circuit for starting. When the
engine has warmed up, push it in to close the
circuit.
HOT STARTER LEVER
The hot starter lever 1 is used when starting a
warm engine.
Use the hot starter lever when starting the
engine again immediately after it was stopped
(the engine is still warm). Pulling the hot starter
lever injects secondary air to thin the air-fuel
mixture temporarily, allowing the engine to be
started more easily.

GEN
INFO
1 - 13
DECOMPRESSION LEVER
DECOMPRESSION LEVER
An auto decompression device is standard equipment on the machine. There is no need to operate
the decompression lever in normal use because the auto decompression device is working.
Use the decompression lever when the engine fails to start or when you want to step down the kick
starter with a lighter force.
For engine starting failure, refer to “STARTING AND BREAK-IN”.
Installation (Supplied for Europe and optional for other destinations)
For installation, follow the steps below.
Order Part name Q’ty Remarks
1 Oil seal 1
2 Torsion spring 1
3 Decompression shaft 1
4 Decompression cable guide 1
5 Flange bolt 1 M 6 × 1.0 [L=14 mm (0.55 in)]
6 Decompression cable 1
7 Decompression lever 1
8 Boot 1
9 Decompression lever holder (upper) 1
10 Collar 1
11 Panhead screw 1 M 5 × 0.8 [L=20 mm (0.79 in)]
12 Nut 1 M 5 × 0.8
13 Decompression lever holder (lower) 1
14 Hexagon bolt 2 M 5 × 0.8 [L=16 mm (0.63 in)]
14
13
11
10 8
7
9
12 6
5
4
1
2
3
T R..10 Nm (1.0 m •
kg, 7.2 ft • Ib)
T R..7 Nm (0.7 m •
kg, 5.1 ft • Ib)
T R..4 Nm (0.4 m •
kg, 2.9 ft • Ib)
B
B
B
B
BE

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GEN
INFO
DECOMPRESSION LEVER
INSTALLATION OF DECOMPRESSION
LEVER
Preparations
1. Remove the seat.
2. Drain the coolant.
Refer to “COOLANT REPLACEMENT”
section in the CHAPTER 3.
3. Remove:
Radiator
Refer to “RADIATOR” section in the
CHAPTER 4.
Cylinder head cover
Refer to “CAMSHAFTS” section in the
CHAPTER 4.
Number plate
4. Remove:
Plug 1
Bolt 2
Plain washer 3
NOTE:
Make a hole in the resin side a and remove
the plug.
Installation
1. Install:
Oil seal 1
NOTE:
Install the oil seal, as shown, where the plug
was removed.
Apply the lithium soap base grease on the oil
seal lip.
2. Install:
Torsion spring 1
Decompression shaft 2
Plain washer 3
Bolt (decompression shaft) 4
Decompression cable guide 5
Bolt (decompression cable guide) 6
Decompression cable 7
NOTE:
When installing the decompression shaft,
install the torsion spring in the location as
shown.
For the decompression shaft securing bolt
and plain washer, use the ones removed
from the same machine.
Apply the engine oil on the decompression
shaft.
23
1 a
1B
T R..7 Nm (0.7 m · kg, 5.1 ft · lb)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)

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GEN
INFO
DECOMPRESSION LEVER ADJUSTMENT
1. Check:
Decompression lever free play
2. Adjust:
Decompression lever free play
FOR PROPER USE
CAUTION:
Never use the decompression lever after
the engine is started. The engine may be
damaged if you use the decompression
lever while it is running.
NOTE:
Refer to “STARTING AND BREAK-IN” for
starting except when “The engine fails to start.”
The engine fails to start
Pull the decompression lever to the handlebar,
and while holding the lever, kick the kick
starter 10 to 20 times to clear the engine of the
rich mixture.Checking steps:
Remove the timing plug.
Turn the crankshaft counterclockwise to
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.
Check the free play c.
Free play:
3 ~ 5 mm (0.12 ~ 0.20 in)
Adjustment steps:
Loosen the locknut 1.
Turn the adjuster 2 in or out until the
adjustment is suitable.
Tighten the locknut.
CAUTION:
After the adjustment, start the engine
and make sure that the engine does not
stop when the handlebars are turned
fully both ways. If the decompression
cable is too tense, the engine will stop by
the decompression system.
2 1 c
DECOMPRESSION LEVER

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GEN
INFO
FUEL
Always use the recommended fuel as stated
below. Also, be sure to use new gasoline the
day of a race.
CAUTION:
Use only unleaded gasoline. The use of
leaded gasoline will cause severe damage
to the engine internal parts such as valves,
piston rings, and exhaust system, etc.
NOTE:
If knocking or pinging occurs, use a different
brand of gasoline or higher octane grade.
WARNING
For refueling, be sure to stop the engine
and use enough care not to spill any fuel.
Also be sure to avoid refueling close to a
fire.
Refuel after the engine, exhaust pipe, etc.
have cooled off.
Recommended fuel:
Except for ZA:
Premium unleaded gasoline
only with a research octane
number of 95 or higher.
For ZA:
Premium gasoline
FUEL