Yamaha Wr 450 F Owners Manual

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ENGCARBURETOR
15. Install:
Diaphragm (accelerator pump) 1 
Spring 2 
O-ring 3
Cover 4 
Hose holder (drain hose) 5
Screw (cover) 6 
NOTE:
Install the diaphragm (accelerator pump) with
its mark a facing the spring.
16. Install:
Jet needle 1 
Collar 2 
Spring 3 
Needle holder 4 
Throttle valve plate 5 
To throttle valve 6.
5
6
1
2
3
4
17. Install:
Throttle valve assembly 1 
Screw (throttle shaft) 2 
NOTE:
Install the valve lever rollers 3 into the slits a
of the throttle valve.
18. Install:
O-ring 1 
Valve lever housing cover 2 
Bolt (valve lever housing cover) 3 
19. Install:
Carburetor breather hose 1 
Refer to “CABLE ROUTING DIA-
GRAM” section in the CHAPTER 2. 
						

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ENGCARBURETOR
Accelerator pump timing adjustment
Adjustment steps:
NOTE:
In order for the throttle valve height a to
achieve the specified value, tuck under the
throttle valve plate 1 the rod 2 etc. with
the same outer diameter as the specified
value.
Throttle valve height:
3.1 mm (0.122 in)
Fully turn in the accelerator pump adjust-
ing screw 3.
Check that the link lever 4 has free play
b by pushing lightly on it.
Gradually turn out the adjusting screw
while moving the link lever until it has no
more free play.
Carburetor installation
1. Install:
Carburetor joint 1 
NOTE:
Install the projection a on the cylinder head
between the carburetor joint slots b.
T R..3 Nm (0.3 m · kg, 2.2 ft · lb)
2. Install:
Carburetor 1 
NOTE:
Install the projection a between the carburetor
joint slots.
3. Install:
Hot starter plunger 1
1
T R..2 Nm (0.2 m · kg, 1.4 ft · lb) 
						

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ENG
4. Tighten:
Screw (air cleaner joint) 1 
Screw (carburetor joint) 2 
T R..3 Nm (0.3 m · kg, 2.2 ft · lb)
T R..3 Nm (0.3 m · kg, 2.2 ft · lb)
5. Install:
Throttle cable (pull) 1 
Throttle cable (return) 2 
6. Adjust:
Throttle grip free play
Refer to “THROTTLE CABLE ADJUST-
MENT” section in the CHAPTER 3.
2
1
T R..4 Nm (0.4 m · kg, 2.9 ft · lb)
T R..11 Nm (1.1 m · kg, 8.0 ft · lb)
7. Install:
Throttle cable cover 1 
Screw (throttle cable cover) 2 
2 1
T R..4 Nm (0.4 m · kg, 2.9 ft · lb)
8. Install:
TPS (throttle position sensor) coupler
1 
Clamp 2 
Refer to “CABLE ROUTING DIA-
GRAM” section in the CHAPTER 2.
9. Install:
Clamp 1 
Refer to “CABLE ROUTING DIA-
GRAM” section in the CHAPTER 2.
1
CARBURETOR 
						

							 
4 - 21
ENG
 
CAMSHAFTS
CAMSHAFTS 
CYLINDER HEAD COVER 
Extent of removal:  
1  
 Cylinder head cover removal
Extent of removal Order Part name Q’ty Remarks  
CYLINDER HEAD COVER 
REMOVAL  
Preparation for removal Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE 
COVERS” section.
Carburetor Refer to “CARBURETOR” section.
1 Spark plug 1
2 Engine upper bracket (right) 1
3 Engine upper bracket (left) 1
4 Cylinder head breather hose 1
5 Oil tank breather hose 1
6 Bolt (cylinder head cover) 2
7 Cylinder head cover 1
8 Gasket 1
9 Timing chain guide (upper) 1
1 
						

							 
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ENG
 
CAMSHAFTS 
CAMSHAFTS 
Extent of removal:  
1  
 Camshaft removal
Extent of removal Order Part name Q’ty Remarks  
CAMSHAFTS REMOVAL  
1 Timing plug 1
Refer to “REMOVAL POINTS”. 2 Straight plug 1
3 Tensioner cap bolt 1
4 Timing chain tensioner 1
5 Gasket 1
6 Bolt (camshaft cap) 10
7 Camshaft cap 2
8 Clip 2
9 Exhaust camshaft 1
10 Intake camshaft 1
1 
						

							 
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ENG
 
CAMSHAFTS 
REMOVAL POINTS
Camshaft  
1. Remove: 
 
Timing plug   
1  
  
 
Straight plug   
2  
 
2. Align: 
 
“I” mark
With stationary pointer.  
Checking steps: 
 
Turn the crankshaft counterclockwise with
a wrench. 
 
Align the “I” mark   
a  
 on the rotor with the
stationary pointer   
b  
 on the crankcase
cover. When the “I” mark is aligned with
the stationary pointer, the piston is at the
Top Dead Center (T.D.C.).
NOTE:
 
 
In order to be sure that the piston is at Top
Dead Center, the punch mark   
c  
 on the
exhaust camshaft and the punch mark   
d  
on the intake camshaft must align with the
cylinder head surface, as shown in the
illustration. 
 
If there is no clearance, rotate the crank- 
shaft counterclockwise one turn.
1
2
b
a
 
3. Loosen: 
 
Tensioner cap bolt   
1  
 
4. Remove: 
 
Timing chain tensioner   
2  
 
5. Remove: 
 
Bolt (camshaft cap)   
1  
  
 
Camshaft caps   
2  
 
NOTE:
 
Remove the bolts (camshaft cap) in a criss- 
cross pattern, working from the outside in.
CAUTION:
 
The bolts (camshaft cap) must be removed
evenly to prevent damage to the cylinder 
head, camshafts or camshaft caps.
1
2
1
2 
						

							 
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ENG
 
CAMSHAFTS 
6. Remove: 
 
Clips  
 
Exhaust camshaft  
1  
  
 
Intake camshaft  
2  
 
NOTE:
 
Attach a wire  
3 
 to the timing chain to prevent 
it from falling into the crankcase.
1
2
3
 
INSPECTION
Camshaft 
1. Inspect:  
 
Cam lobes 
Pitting/scratches/blue discoloration  
→  
 
Replace.
2. Measure: 
 
Cam lobes length  
a 
 and  
b  
 
Out of specification  
→ 
 Replace.  
Cam lobes length:
Intake: 
a 
31.200 ~ 31.300 mm 
(1.2283 ~ 1.2323 in)
: 31.100 mm 
(1.2244 in) 
b 
22.550 ~ 22.650 mm 
(0.8878 ~ 0.8917 in)
: 22.450 mm 
(0.8839 in)
Exhaust: 
a 
30.950 ~ 31.050 mm 
(1.2185 ~ 1.2224 in)
: 30.850 mm 
(1.2146 in) 
b 
22.494 ~ 22.594 mm 
(0.8856 ~ 0.8895 in)
: 22.394 mm 
(0.8817 in) 
3. Measure: 
 
Runout (camshaft) 
Out of specification  
→ 
 Replace.  
Runout (camshaft):
Less than 0.03 mm (0.0012 in) 
						

							 
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ENG
 
CAMSHAFTS 
4. Measure: 
 
Camshaft-to-cap clearance 
Out of specification  
→ 
 Measure cam-
shaft journal diameter.  
Camshaft-to-cap clearance:
0.020 ~ 0.054 mm 
(0.0008 ~ 0.0021 in)
: 0.08 mm (0.003 in)
Measurement steps: 
 
Install the camshaft onto the cylinder
head. 
 
Position a strip of Plastigauge 
®
 
  
1 
 onto the
camshaft. 
 
Install the circlip, dowel pins and camshaft
caps.
T R..
 
Bolt (camshaft cap):
10 Nm (1.0 m • kg, 7.2 ft • lb)
NOTE:
 
 
Tighten the bolts (camshaft cap) in a criss-
cross pattern from innermost to outer
caps. 
 
Do not turn the camshaft when measuring 
clearance with the Plastigauge
®.
Remove the camshaft caps and measure
the width of the Plastigauge
® 1.
5. Measure: 
Camshaft journal diameter a 
Out of specification → Replace the
camshaft. 
Within specification → Replace cam-
shaft case and camshaft caps as a set. 
Camshaft sprocket
1. Inspect:
Camshaft sprocket 1 
Wear/damage → Replace the camshaft
assembly and timing chain as a set.
Camshaft journal diameter: 
21.967 ~ 21.980 mm 
(0.8648 ~ 0.8654 in) 
						

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ENGCAMSHAFTS
Decompression system
1. Check:
Decompression system
Checking steps:
Check that the decompressor cam 1
moves smoothly.
Check that the decompressor lever pin 2
projects from the camshaft.
Timing chain tensioner
1. Check:
While pressing the tensioner rod lightly
with fingers, use a thin screwdriver 1
and wind the tensioner rod up fully
clockwise.
When releasing the screwdriver by
pressing lightly with fingers, make sure
that the tensioner rod will come out
smoothly.
If not, replace the tensioner assembly.
ASSEMBLY AND INSTALLATION
1. Install:
Exhaust camshaft 1 
Intake camshaft 2 
Installation steps:
Turn the crankshaft counterclockwise until
the “I” mark a on the rotor is aligned with
the stationary pointer b on the crankcase
cover.
NOTE:
Apply the molybdenum disulfide oil on the
camshafts.
Apply the engine oil on the decompression
system. 
						

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ENGCAMSHAFTS
Fit the timing chain 3 onto both camshaft
sprockets and install the camshafts on the
cylinder head.
NOTE:
The camshafts should be installed onto the
cylinder head so that the exhaust cam
sprocket punch mark c and the intake cam
sprocket punch mark d align with the sur-
face of the cylinder head.
CAUTION:
Do not turn the crankshaft during the
camshaft installation. Damage or
improper valve timing will result.
Install the clips and camshaft caps 4.
T R..
Bolt (camshaft cap):
10 Nm (1.0 m • kg, 7.2 ft • lb)
NOTE:
Apply the engine oil on the thread and con-
tact surface of the bolts (camshaft cap) 5.
Tighten the bolts (camshaft cap) in a criss-
cross pattern.
CAUTION:
The bolts (camshaft cap) must be tight-
ened evenly, or damage to the cylinder
head, camshaft caps, and camshaft will
result.
5
4
E
2. Install:
Timing chain tensioner
Installation steps:
While pressing the tensioner rod lightly
with fingers, use a thin screwdriver and
wind the tensioner rod up fully clockwise.