2015 YAMAHA YZ450F Owners Manual

VALVES AND VALVE SPRINGS
5-30
EAS1SL5226INSTALLING THE VALVES
1. Clean:
• Valve stem end
2. Lubricate:
• Valve stem “1”
• Valve stem seal “2”
3. Install:
• Spring seat “1”
• Valve stem seal “2”
•Valve “3”
• Valve spring “4”
• Valve spring retainer “5”
(to the cylinder head)
TIP
• Make sure each valve is installed in its original
place.
• Install the valve springs with the larger pitch
“a” facing up.4. Install:
• Valve cotter “1”
TIP
Install the valve cotters by compressing the
valve spring with the valve spring compressor
“2” and the valve spring compressor adapter
“3”.
5. To fasten the valve cotters onto the valve
stem, lightly tap the valve tip with a soft-face
hammer.
ECA13800
NOTICE
Hitting the valve tip with excessive force
could damage the valve. Recommended lubricant
Molybdenum disulfide oil
b. Smaller pitch
New
Valve spring compressor
90890-04019
YM-04019
Valve spring compressor adapter
22 mm
90890-04108
YM-04108

VALVES AND VALVE SPRINGS
5-31
6. Lubricate:
• Adjusting pad “1”
• Valve lifter “2”
7. Install:
• Adjusting pad
• Valve lifter
TIP
• Check that the valve lifter turns smoothly
when rotated with your finger.
• Make sure that the valve lifter and the adjust-
ing pad are reinstalled in their original posi-
tions.
E
1 2

CYLINDER AND PISTON
5-32
EAS1SL5227
CYLINDER AND PISTON
Removing the cylinder and piston
Order Part name Q’ty Remarks
Cylinder headRefer to “CYLINDER HEAD” on page 5-19.
1Cylinder body
1
2Gaskets
1
3Dowel pin
2
4Piston pin clip
2
5Piston pin
1
6Piston
1
7Piston ring set
1
For installation, reverse the removal proce-
dure.
1
2
3
4
4
5
6
7
10 Nm (1.0 m kgf, 7.2 ft Ibf)T.R.
10 Nm (1.0 m kgf, 7.2 ft Ibf)T.R.
E
E
New
New
New
LT
E

CYLINDER AND PISTON
5-33
EAS1SL5228REMOVING THE PISTON
1. Remove:
• Piston pin clip “1”
• Piston pin “2”
• Piston “3”
ECA13810
NOTICE
Do not use a hammer to drive the piston pin
out.
TIP
• Before removing the piston pin clip, cover the
crankcase opening with a cloth to prevent the
piston pin clip from falling into the crankcase.
• Before removing the piston pin, deburr the
piston pin clip’s groove and the piston pin’s
bore area. If the piston pin groove is deburred
and the piston pin is still difficult to remove,
use the piston pin puller set “4”.
2. Remove:
• Top ring
• 2nd ring
• Oil ring
TIP
When removing a piston ring, open the end gap
with your fingers and lift the opposite end gap
of the piston ring over the piston crown.
EAS1SL5229CHECKING THE CYLINDER AND PISTON
1. Check:
• Piston wall (Sidewall)
• Cylinder wall
Vertical scratches  Replace the cylinder,
and replace the piston and piston rings as a
set.
2. Measure:
• Piston-to-cylinder clearance
▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼▼
a. Measure the cylinder bore with the cylinder
bore gauge.
TIP
Measure cylinder bore by taking side-to-side
and front-to-back measurements of the cylin-
der. Then, find the average of the measure-
ments. Piston pin puller set
90890-01304
Piston pin puller
YU-01304
1
Bore
97.000–97.010 mm (3.8189–
3.8193 in)
Taper limit
0.050 mm (0.0020 in)
Out of round limit
0.050 mm (0.0020 in)
Cylinder bore = maximum of D
1–D6
Taper limit = (maximum of D1or D2) - (maxi-
mum of D
5 or D6)
Out of round limit = maximum of D
1, D3 or D5
- minimum of D
2, D4 or D6

CYLINDER AND PISTON
5-34
b. If out of specification, rebore or replace the
cylinder, and replace the piston and the pis-
ton rings as a set.
c. Measure the piston outside diameter D “a” at
the measurement position H “b” with the mi-
crometer.
d. If out of specification, replace the cylinder,
the piston, and the piston rings as a set.
e. Calculate the piston-to-cylinder clearance
with the following formula.
f. If out of specification, replace the cylinder,
the piston, and the piston rings as a set.
▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲
EAS1SL5230CHECKING THE PISTON RINGS
1. Measure:
• Piston ring side clearance
Out of specification  Replace the piston
and piston rings as a set.
TIP
Before measuring the piston ring side clear-
ance, eliminate any carbon deposits from the
piston ring grooves and piston rings.2. Install:
• Piston rings
TIP
Level the piston ring into the cylinder with the
piston.
3. Measure:
• Piston ring end gap
Out of specification  Replace the piston
ring.
TIP
The oil ring expander’s end gap cannot be
measured. If the oil ring rail’s gap is excessive,
replace all three oil rings. Diameter D
96.955–96.970 mm (3.8171–
3.8177 in)
Measurement position H
9.0 mm (0.35 in)
Piston-to-cylinder clearance =
Cylinder bore - Piston diameter
Piston-to-cylinder clearance
0.030–0.055 mm (0.0012–0.0022
in)
Limit
0.15 mm (0.006 in)
ba
Ring side clearance
0.015–0.065 mm (0.0006–0.0026
in)
Limit
0.120 mm (0.0047 in)
2nd ring
0.020–0.060 mm (0.0008–0.0024
in)
Limit
0.120 mm (0.0047 in)
a. 10 mm (0.39 in)

CYLINDER AND PISTON
5-35
EAS1SL5231CHECKING THE PISTON PIN
1. Check:
• Piston pin
Blue discoloration/grooves  Replace the
piston pin and then check the lubrication
system.
2. Measure:
• Piston pin outside diameter “a”
Out of specification  Replace the piston
pin.
3. Measure:
• Piston pin bore inside diameter “b”
Out of specification  Replace the piston.
EAS1SL5232INSTALLING THE PISTON AND CYLINDER
1. Install:
• Oil ring expander “1”
• Lower oil ring rail “2”
• Upper oil ring rail “3”
• 2nd ring “4”
• Top ring “5”
TIP
Be sure to install the piston rings so that the
manufacturer’s marks or numbers face up.
2. Install:
• Piston “1”
• Piston pin “2”
• Piston pin clip “3”
TIP
• Apply the engine oil to the piston pin.
• Install the piston with the F mark “a” on it
pointing to its intake (front) side.
• Before installing the piston pin clip, cover the
crankcase opening with a cloth to prevent the
clip from falling into the crankcase. Piston ring end gap
Top ring
End gap (installed)
0.20–0.30 mm (0.0079–0.0118 in)
Limit
0.55 mm (0.0217 in)
End gap (installed)
0.35–0.50 mm (0.0138–0.0197 in)
Limit
0.85 mm (0.0335 in)
Oil ring
End gap (installed)
0.20–0.50 mm (0.0079–0.0197 in)
Piston pin outside diameter
17.991–18.000 mm (0.7083–
0.7087 in)
Limit
17.971 mm (0.7075 in)
Piston pin bore inside diameter
18.004–18.015 mm (0.7088–
0.7093 in)
Limit
18.045 mm (0.7104 in)
b
New

CYLINDER AND PISTON
5-36
3. Lubricate:
•Piston
• Piston rings
• Cylinder
4. Offset:
• Piston ring end gap
5. Install:
• Cylinder gasket
• Dowel pin
• Cylinder
TIP
• While compressing the piston rings with one
hand, install the cylinder with the other hand.
• Pass the timing chain and timing chain guide
(exhaust side) through the timing chain cavity.
a. Top ring
b. 2nd ring
c. Upper oil ring rail
d. Oil ring expander
e. Lower oil ring rail
Cylinder bolt
10 Nm (1.0 m·kgf, 7.2 ft·lbf)
1
3
2 a
3
ac
eb d
15
15
15
1515
New
T R..

CLUTCH
5-37
EAS1SL5233
CLUTCH
Removing the clutch
Order Part name Q’ty Remarks
Engine oilDrain.
Refer to “CHANGING THE ENGINE OIL” on
page 3-15.
Brake pedal Refer to “ENGINE REMOVAL” on page 5-1.
1 Clutch cable 1 Disconnect.
2 Clutch cover 1
3 O-ring 1
4 Clutch spring 6
5 Pressure plate 1
6 Push rod 1 1
7 Circlip 1
8Washers 1
9 Bearing 1
10 Ball 1
11 Push rod 2 1
12 Friction plate 1 5
13 Clutch plate 7
LS
New
New
New
2
3 45
78961011
13
12
12
18
1
14
13
13
17
16
15
T.R.
T.R.
T.R.
T.R.
LT