Yamaha Wr 450 F Owners Manual

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ENGVALVES AND VALVE SPRINGS
9. Lap:
Valve face
Valve seat
NOTE:
After refacing the valve seat or replacing the
valve and valve guide, the valve seat and
valve face should be lapped.
Lapping steps:
Apply a coarse lapping compound to the
valve face.
CAUTION:
Do not let the compound enter the gap
between the valve stem and the guide.
Apply molybdenum disulfide oil to the
valve stem.
Install the valve into the cylinder head.
Turn the valve until the valve face and
valve seat are evenly polished, then clean
off all of the compound.
NOTE:
For best lapping results, lightly tap the valve
seat while rotating the valve back and forth
between your hands.
Apply a fine lapping compound to the
valve face and repeat the above steps.
NOTE:
After every lapping operation be sure to
clean off all of the compound from the valve
face and valve seat.
Apply Mechanic’s blueing dye (Dykem) to
the valve face.
Install the valve into the cylinder head.
Press the valve through the valve guide
and onto the valve seat to make a clear
pattern.
Measure the valve seat width again. If the
valve seat width is out of specification,
reface and relap the valve seat. 
						

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ENGVALVES AND VALVE SPRINGS
Valve spring
1. Measure:
Valve spring free length a 
Out of specification → Replace.
2. Measure:
Compressed spring force a 
Out of specification → Replace.
bInstalled length
Free length (valve spring):
Intake:
37.03 mm (1.46 in)
: 35.17 mm (1.38 in)
Exhaust:
37.68 mm (1.48 in)
: 35.79 mm (1.41 in)
Compressed spring force:
Intake:
111.3 ~ 127.9 N at 27.87 mm
(11.3 ~ 13.0 kg at 27.87 mm, 
24.91 ~ 28.66 lb at 1.10 in)
Exhaust:
127.4 ~ 146.4 N at 27.38 mm
(13.0 ~ 14.9 kg at 27.38 mm,
28.66 ~ 32.85 lb at 1.08 in)
3. Measure:
Spring tilt a 
Out of specification → Replace.
Spring tilt limit:
Intake:
2.5˚/1.61 mm (0.063 in)
Exhaust:
2.5˚/1.65 mm (0.065 in)
Valve lifter
1. Inspect:
Valve lifter
Scratches/damage → Replace both lift-
ers and cylinder head. 
						

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ENGVALVES AND VALVE SPRINGS
Combination of cylinder head and valve 
lifter
1. Combination:
For this combination, match the paint
color on the cylinder head with that on the
valve lifter according to the chart below.
NOTE:
When you purchase a cylinder head, you can-
not designate its size. Choose the valve lifter
that matches the above chart.Combination
Cylinder head mark 
a (color)Valve lifter mark 
b (color)
Blue Blue
Yellow Yellow
Purple Black
ab
ASSEMBLY AND INSTALLATION
1. Apply:
Molybdenum disulfide oil
Onto the valve stem and valve stem
seal.
2. Install:
Valves 1 
Valve spring seats 2 
Valve stem seals 3 
Valve springs 4 
Valve spring retainers 5 
NOTE:
Make sure that each valve is installed in its
original place, also referring to the painted
color as follows.
Intake (middle) a: blue
Intake (right/left) b: gray
Exhaust: not paint
Install the valve springs with the larger pitch
c facing upward.
dSmaller pitch
New 
						

							 
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ENG
 
VALVES 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. 
						

							 
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ENG
 
CYLINDER AND PISTON
CYLINDER AND PISTON 
CYLINDER AND PISTON 
Extent of removal: 
1  
 Cylinder removal  
2  
 Piston removal
Extent of removal Order Part name Q’ty Remarks 
CYLINDER AND PISTON 
REMOVAL  
Preparation for removal Cylinder head Refer to “CYLINDER HEAD” section.
1 Bolt (cylinder) 1
2 Cylinder 1
3 Gasket 1
4 Dowel pin 2
5 Dowel pin/O-ring 1/1
6 Piston pin clip 2
Use special tool.
Refer to “REMOVAL POINTS”. 7 Piston pin 1
8 Piston 1
9 Piston ring set 1
2
1 
						

							 
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ENG
 
CYLINDER 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. 
						

							 
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ENG
 
CYLINDER AND PISTON 
Cylinder bore “C”95.00 ~ 95.01 mm
(3.7402 ~ 3.7406 in)
Taper limit “T” 0.05 mm (0.002 in)
Out of round “R” 0.05 mm (0.002 in)
“C” = Maximum D
“T” = (Maximum D 
1 
 or D 
2 
) 
– (Maximum D 
5 
 or D 
6 
)
“R” = (Maximum D 
1 
, D 
3 
 or D 
5 
) 
  
– (Minimum D 
2 
, D 
4 
 or D 
6 
) 
 
If out of specification, replace the cylinder,
and replace the piston and piston rings as
set. 
2nd step: 
 
Measure the piston skirt diameter “P” with
a micrometer. 
a 
8 mm (0.315 in) from the piston bottom edge 
Piston size “P”
Standard94.945 ~ 94.960 mm 
(3.738 ~ 3.739 in) 
 
If out of specification, replace the piston
and piston rings as a set. 
3rd step: 
 
Calculate the piston-to-cylinder clearance
with following formula: 
Piston-to-cylinder clearance =
Cylinder bore “C” –
Piston skirt diameter “P” 
Piston-to-cylinder clearance:
0.040 ~ 0.065 mm 
(0.0016 ~ 0.0026 in)
: 0.1 mm (0.004 in) 
 
If out of specification, replace the cylinder,
and replace the piston and piston rings as
set. 
						

							 
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ENG
 
CYLINDER AND PISTON 
Piston ring 
1. Measure: 
 
Ring side clearance
Use a feeler gauge  
1 
. 
Out of specification  
→ 
 Replace the pis-
ton and rings as a set.
NOTE:
 
Clean carbon from the piston ring grooves and 
rings before measuring the side clearance.
2. Position: 
 
Piston ring 
(in cylinder)
NOTE:
 
Insert a ring into the cylinder and push it
approximately 10 mm (0.39 in) into the cylin-
der. Push the ring with the piston crown so that
the ring will be at a right angle to the cylinder 
bore. 
a 
10 mm (0.39 in) 
Side clearance:
Standard 
Top ring0.030 ~ 0.065 mm 
(0.0012 ~ 0.0026 in)0.12 mm 
(0.005 in)
2nd ring0.020 ~ 0.055 mm 
(0.0008 ~ 0.0022 in)0.12 mm 
(0.005 in) 
3. Measure: 
 
Ring end gap 
Out of specification  
→ 
 Replace.
NOTE:
 
You cannot measure the end gap on the
expander spacer of the oil control ring. If the oil
control ring rails show excessive gap, replace 
all three rings. 
End gap:
Standard 
Top ring0.20 ~ 0.30 mm
(0.008 ~ 0.012 in)0.55 mm
(0.022 in)
2nd ring0.35 ~ 0.50 mm
(0.014 ~ 0.020 in)0.85 mm
(0.033 in)
Oil ring0.20 ~ 0.50 mm
(0.01 ~ 0.02 in)— 
						

							 
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ENG
 
CYLINDER AND PISTON 
Piston pin 
1. Inspect: 
 
Piston pin
Blue discoloration/grooves  
→ 
 Replace,
then inspect the lubrication system.
2. Measure: 
 
Piston pin-to-piston clearance 
ASSEMBLY AND INSTALLATION
Piston 
1. Install: 
 
Piston rings
Onto the piston.
NOTE:
 
 
Be sure to install the piston rings so that the
manufacturer’s marks or numbers are
located on the upper side of the rings. 
 
Lubricate the piston and piston rings liberally 
with engine oil. 
Measurement steps:
Measure the outside diameter (piston pin)
a.
If out of specification, replace the piston
pin.
Outside diameter (piston pin):
17.991 ~ 18.000 mm
(0.7083 ~ 0.7087 in)
Measure the inside diameter (piston) b.
Inside diameter (piston):
18.004 ~ 18.015 mm
(0.7088 ~ 0.7093 in)
Calculate the piston pin-to-piston clear-
ance with the following formula.
Piston pin-to-piston clearance =
Inside diameter (piston) b –
Outside diameter (piston pin) a 
If out of specification, replace the piston.
Piston pin-to-piston clearance:
0.004 ~ 0.024 mm 
(0.00016 ~ 0.00094 in)
: 0.07 mm (0.003 in) 
						

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ENGCYLINDER AND PISTON
2. Position:
Top ring
2nd ring
Oil ring
Offset the piston ring end gaps as
shown.
aTop ring end
b2nd ring end
cOil ring end (upper)
dOil ring
eOil ring end (lower)
3. Install:
Piston 1 
Piston pin 2 
Piston pin clips 3 
NOTE:
Apply engine oil onto the piston pin and pis-
ton.
Be sure that the arrow mark a on the piston
points to the exhaust side of the engine.
Before installing the piston pin clip, cover the
crankcase with a clean rag to prevent the
piston pin clip from falling into the crankcase.
Install the piston pin clips with their ends fac-
ing downward.
4. Lubricate:
Piston
Piston rings
Cylinder
NOTE:
Apply a liberal coating of engine oil.
Cylinder
1. Install:
Dowel pins
O-ring
Gasket 1 
Cylinder 2 
NOTE:
Install the cylinder with one hand while com-
pressing the piston rings with the other hand.
CAUTION:
Pass the timing chain 3 through the tim-
ing chain cavity. 
Be careful not to damage the timing chain
guide 4 during installation.
2. Install:
Bolt (cylinder)
45°
135°135°
a
b ced
3New
New
New
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)