head YAMAHA WR 450F 2003 Service Manual

4 - 43
ENGCYLINDER AND PISTON
REMOVAL POINTS
Piston
1. Remove:
Piston pin clips 1
Piston pin 2
Piston 3
NOTE:
Put identification marks on each piston head
for reference during reinstallation.
Before removing each piston pin, deburr the
clip groove and pin hole area. If the piston
pin groove is deburred and the piston pin is
still difficult to remove, use the piston pin
puller 4.
CAUTION:
Do not use a hammer to drive the piston
pin out.
Piston ring
1. Remove:
Piston rings
NOTE:
Spread the end gaps apart while at the same
time lifting the piston ring over the top of the
piston crown, as shown in the illustration.
INSPECTION
Cylinder and piston
1. Inspect:
Cylinder and piston walls
Vertical scratches → Replace cylinder
and piston.
2. Measure:
Piston-to-cylinder clearance
Piston pin puller:
YU-1304/90890-01304
Measurement steps:
1st step:
Measure the cylinder bore “C” with a cylin-
der bore gauge.
NOTE:
Measure the cylinder bore “C” in parallel to
and at right angles to the crankshaft. Then,
find the average of the measurements.

4 - 82
ENG
10. Install:
Engine guard 1
Clamp 2
Bolt [engine guard (front)] 3
Bolt [engine guard (rear)] 4
Cylinder head breather hose 5
T R..34 Nm (3.4 m · kg, 24 ft · lb)
T R..23 Nm (2.3 m · kg, 17 ft · lb)
11. Connect:
AC magneto lead
Refer to “CABLE ROUTING DIA-
GRAM” section in the CHAPTER 2.
12. Install:
Shift pedal 1
Bolt (shift pedal)
NOTE:
When installing the shift pedal onto the shift
shaft, be sure that the center of the shift pedal
is about 1 mm (0.04 in) a above the top of the
footrest.
T R..12 Nm (1.2 m · kg, 8.7 ft · lb)
AC MAGNETO AND STARTER CLUTCH

4 - 83
ENGENGINE REMOVAL
EC4M0000
ENGINE REMOVAL
Extent of removal Order Part name Q’ty Remarks
ENGINE REMOVAL
Preparation for removal Hold the machine by placing the
suitable stand under the frame.
WARNING
Support the machine securely so there is no
danger of it falling over.
Drain the engine oil Refer to “ENGINE OIL REPLACEMENT”
section in the CHAPTER 3.
Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Carburetor Refer to “CARBURETOR” section.
Exhaust pipe and silencer Refer to “EXHAUST PIPE AND
SILENCER” section.
Clutch cable and guide Disconnect at the engine side.
Radiator Refer to “RADIATOR” section.
Shift pedal Refer to “AC MAGNETO AND
STARTER CLUTCH” section.
Cylinder head breather hose and
oil tank breather hoseRefer to “CAMSHAFTS” section.
Ignition coil
Disconnect the AC magneto lead.

4 - 95
ENGCRANKCASE AND CRANKSHAFT
EC4N5000
ASSEMBLY AND INSTALLATION
Crankshaft bearing
1. Install:
Bearing
Bearing stopper
Bolt (bearing stopper)
Screw (bearing stopper)
Screw [bearing stopper (crankshaft)] 1
To crankcase (left and right).
NOTE:
Install the bearing by pressing its outer race
parallel.
To prevent the screw [bearing stopper
(crankshaft)] from becoming loose, crush the
screw head periphery a into the concave b
using a punch etc. In so doing, take care not
to damage the screwdriver receiving hole in
the screw head.
New
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
a
b
1
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
Crankshaft
1. Install:
Crankshaft 1
Use the crankshaft installing tool 2, 3,
4 and 5.
ÅFor USA and CDN
ıExcept for USA and CDN
Crankshaft installing pot 2:
YU-90050/90890-01274
Crankshaft installing bolt 3:
YU-90050/90890-01275
Adaptor (M12) 4:
YU-90063/90890-01278
Spacer (crankshaft installer) 5:
YM-91044/90890-04081
Å
ı

5 - 27
CHASFRONT FORK
EC550000
FRONT FORK
Extent of removal:1 Front fork removal
Extent of removal Order Part name Q’ty Remarks
Preparation for removalFRONT FORK REMOVAL
Hold the machine by placing the
suitable stand under the engine.
WARNING
Support the machine securely so there is no
danger of it falling over.
Front wheel Refer to “FRONT WHEEL AND REAR
WHEEL” section.
Front caliper Refer to “FRONT BRAKE AND REAR
BRAKE” section.
Headlight
Handlebar Refer to “HANDLEBAR” section.
1 Protector 1
2 Brake hose holder 2
3 Pinch bolt (handle crown) 2 Only loosening.
4 Cap bolt 1Loosen when disassembling the front fork.
5 Pinch bolt (under bracket) 2 Only loosening.
6 Front fork 1
1

5 - 30
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 - 40
CHAS
EC5B0000
HANDLEBAR
Extent of removal:1 Handlebar removal
Extent of removal Order Part name Q’ty Remarks
Preparation for removalHANDLEBAR REMOVAL
Headlight
1 Hot starter cable 1 Disconnect at the lever side.
2 Hot starter lever holder 1
3 Clutch cable 1 Disconnect at the lever side.
4 Clutch lever holder 1 Disconnect the clutch switch lead.
5“ENGINE STOP” button 1 Disconnect the “ENGINE STOP” button
lead.
6 Lights switch 1
7 Master cylinder 1 Refer to “REMOVAL POINTS”.
8 Start switch 1 Disconnect the start switch lead.
9 Throttle cable cap 1
10 Throttle cable #2 (pushed) 1 Disconnect at the throttle side.
11 Throttle cable #1 (pulled) 1 Disconnect at the throttle side.
12 Grip (right) 1 Refer to “REMOVAL POINTS”.
13 Tube guide 1
14 Cover (grip cap) 1
15 Grip (left) 1 Refer to “REMOVAL POINTS”.
16 Handlebar holder (upper) 2
17 Handlebar 1
1
HANDLEBAR

5 - 46
CHAS
EC560000
STEERING
Extent of removal:1 Under bracket removal2 Bearing removal
Extent of removal Order Part name Q’ty Remarks
STEERING REMOVAL
WARNING
Support the machine securely so there is no
danger of it falling over.
Refer to “HANDLEBAR” section. Preparation for removal Hold the machine by placing the
suitable stand under the engine.
Headlight
Handlebar
Hose guide
Front fender
1 Coupler bracket 1
2 Trip meter 1
3 Main switch 1 Disconnect the main switch lead.
4 Steering shaft cap 1
5 Steering shaft nut 1
6 Front fork 2 Refer to “FRONT FORK” section.
7 Handle crown 1
8 Ring nut 1 Use special tool.
Refer to “REMOVAL POINTS”.
9 Under bracket 1
10 Ball race cover 1
2
1
STEERING

5 - 50
CHAS
4. Install:
Plain washer 1
Ring nut 2
Tighten the ring nut using the ring nut
wrench 3.
Refer to “STEERING HEAD INSPEC-
TION AND ADJUSTMENT” section in
the CHAPTER 3.
T R..7 Nm (0.7 m · kg, 5.1 ft · lb)
5. Check the steering shaft by turning it lock
to lock. If there is any binding, remove
the steering shaft assembly and inspect
the steering bearings.
6. Install:
Plain washer 1
7. Install:
Front fork 1
Handle crown 2
Main switch 3
Coupler bracket 4
Hose guide bracket 5
NOTE:
Install the coupler bracket on the outside of
the hose guide bracket.
Temporarily tighten the pinch bolts (under
bracket).
Do not tighten the pinch bolts (handle crown)
yet.
8. Install:
Plain washer 1
Steering shaft nut 2
T R..145 Nm (14.5 m · kg, 105 ft · lb)
STEERING

6 - 1
–+ELEC

ELECTRICAL COMPONENTS AND WIRING DIAGRAM
EC600000
ELECTRICAL
EC610000
ELECTRICAL COMPONENTS AND WIRING DIAGRAM
EC611000
ELECTRICAL COMPONENTS
1
Headlight
2
“ENGINE STOP”
button
3
Clutch switch
4
Diode
5
Starter relay diode
6
TPS (throttle posi-
tion sensor)
7
Starter relay
8
Fuse
9
Starting circuit
cut-off relay
0
Taillight
A
Neutral switch
B
Starter motor
C
AC magneto
D
Rectifier/regulator
E
Ignition coil
F
Spark plug
G
Start switch
H
Lights switch
I
Main switch
J
CDI unit
K
Battery
COLOR CODE
B.......................Black
Br .....................Brown
Gy ....................Gray
L .......................Blue
O ......................Orange
R ......................Red
Sb.....................Sky blue
W......................White
Y.......................Yellow
B/L....................Black/Blue
EC612000
WIRING DIAGRAM
1 2345
678
90
A B
CDEFGH
I
J
K
WR
WR
R
BR/BBr
R
BR/BBr
RW
L/RL/BBB
SbL/W
WY
YW
L/YBBB
WY
RYW
R
LY
B
YLB/L
B
B
ON
OFF
10A
BB
OFF
ON
OFF
STARTSTART
R-BrL/W
BLY
YLB-LB
B
BrL/W
BrL/W
L/B-LB
YL
B
L-B
L/WSb
B/WBBB
W/RB/W
R/BGyBrL/W
ON
STOP
OB
LYSbB/L
W RBrB/W
L/BGyWR/B
B O
L/YSbL/R
R W
Y W
Y W
Y B
B
L
L L
L B
B
B
RRR/B
B Br B
B B B B
L/W
R
R
R R B
R
BrBr
L/W L/W
Br B
L/B
L/B
L/R

Br
R/B
L/B L/W
B/W
W W/RW
RO
L
Y
B/L
O

B
L
Y
B/LSbL/WB/W
B
L/R L/Y L/Y
B
SbSbL/W
BGy
SbBB/LYO
L
∗2
O B
L YL/W
B/L
∗1
C
HD
BI
5
9
G3 4
A 2J
EF
6 7
K8
1
0
∗
2
∗1
∗2: Except for USA
∗1: For USA

B/W .................. Black/White
L/B ................... Blue/Black
L/R ................... Blue/Red
L/Y ................... Blue/Yellow
L/W .................. Blue/White
R/B................... Red/Black