YAMAHA YZ450F 2015 Owners Manual

CAMSHAFT
5-16
EAS1SL5213CHECKING THE DECOMPRESSION SYS-
TEM
1. Check:
• Decompression system
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a. Check that the decompressor cam “1”
moves smoothly.
b. Check that the decompressor lever pin “2”
projects from the camshaft.
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EAS1SL5214INSTALLING THE CAMSHAFTS
1. Install:
• Exhaust camshaft “1”
• Intake camshaft “2”
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a. Turn the crankshaft counterclockwise with a
wrench.
TIP
• Apply molybdenum disulfide oil to the cam-
shafts.
• Apply the engine oil on the decompression
system.
• Fill the cylinder head with engine oil up to the
tops “a” of the valve lifters.b. Align the top dead center (TDC) mark “a” on
the rotor with the alignment mark “b” on the
crankcase cover.
c. Fit the timing chain “3” onto both camshaft
sprockets and install the camshafts on the
cylinder head.
TIP
Make sure that the alignment mark “c” on the
exhaust camshaft sprocket and the alignment
mark “d” on the intake camshaft sprocket are
aligned with the edge of the cylinder head.
ECA33DD029
NOTICE
Do not turn the crankshaft during the cam-
shaft installation. Damage or improper
valve timing will result.
d. Install the clips, the camshaft caps and the
bolts (camshaft cap).
1
2
Bolt (camshaft cap)
10 Nm (1.0 m·kgf, 7.2 ft·lbf)
a
aa
b
a
c 3
d
T R..

CAMSHAFT
5-17
TIP
• Before installing the clips, cover the cylinder
head with a clean cloth to prevent the clips
from coming off into the cylinder head cavity.
• Tighten the bolts to the specified torque in two
or three steps in the proper tightening se-
quence as shown.
ECA33DD030
NOTICE
The bolts (camshaft cap) must be tightened
evenly, or damage to the cylinder head,
camshaft caps, and camshaft will result.
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2. Install:
• Timing chain tensioner
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a. While pressing the tensioner rod lightly with
your fingers, use a thin screwdriver to wind
the tensioner rod up fully clockwise.
b. With the tensioner rod fully wound and the
chain tensioner UP mark “a” facing upward,
install the gasket “1”, the timing chain ten-
sioner “2”, and the gasket “3”, and tighten
the bolt “4”.c. Release the screwdriver, check that the ten-
sioner rod comes out smoothly, and tighten
the gasket “5” and the cap bolt “6”.▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲
3. Turn:
• Crankshaft
Counterclockwise several turns.
4. Check:
• Top dead center (TDC) mark on the rotor
Align with the crankcase alignment mark.
• Camshaft match marks
Align with the cylinder head surface.
Out of alignment  Adjust.
5. Install:
• Timing chain guide (top side) “1”
• Cylinder head cover gasket “2”
• Cylinder head cover “3”
• Bolt (cylinder head cover) “4”
TIP
Before installation, apply the sealant to the cyl-
inder head cover gasket. Bolt (timing chain tensioner)
10 Nm (1.0 m·kgf, 7.2 ft·lbf)
3
4
8
7
15
26
T R..
Tensioner cap bolt
6 Nm (0.6 m·kgf, 4.3 ft·lbf)
Bolt (cylinder head cover)
10 Nm (1.0 m·kgf, 7.2 ft·lbf)
Three Bond No.1215®
90890-85505
T R..
6 5
T R..

CAMSHAFT
5-18
6. Install:
• Cylinder head breather hose
• Spark plug
Spark plug
13 Nm (1.3m·kgf, 9.4 ft·lbf)
4
4
4
3
21
T R..

CYLINDER HEAD
5-19
EAS1SL5215
CYLINDER HEAD
Removing the cylinder head
Order Part name Q’ty Remarks
Seat Refer to “GENERAL CHASSIS” on page 4-1.
Side cover (left/right) Refer to “GENERAL CHASSIS” on page 4-1.
Air scoop (left / right) Refer to “GENERAL CHASSIS” on page 4-1.
Fuel tank Refer to “FUEL TANK” on page 7-1.
Exhaust pipe and silencer Refer to “ENGINE REMOVAL” on page 5-1.
Radiator hose Disconnect.
Coolant temperature sensor coupler Disconnect.
Throttle body Refer to “THROTTLE BODY” on page 7-5.
Camshaft Refer to “CAMSHAFT” on page 5-11.
Upper engine bracket Refer to “ENGINE REMOVAL” on page 5-1.
1 Bolt (cylinder head) 2
2 Bolt (cylinder head) 4
3 Cylinder head 1
4 Cylinder head gasket 1
5 Timing chain guide (intake side) 1
6 Oil check bolt 2
7 66
1st
2nd
Final20 Nm (2.0 m
kgf, 14 ftIbf)T.
R.
30 Nm (3.0 mkgf, 22 ftIbf)
10 Nm (1.0 mkgf, 7.2 ftIbf)T.R.
10 Nm (1.0 mkgf, 7.2 ftIbf)T.R.
15 Nm (1.5 mkgf, 11 ftIbf)T.R.

CYLINDER HEAD
5-20
7 Oil passage plug 1
For installation, reverse the removal proce-
dure.
Removing the cylinder head
Order Part name Q’ty Remarks
7 66
1st
2nd
Final20 Nm (2.0 m
kgf, 14 ftIbf)T.
R.
30 Nm (3.0 mkgf, 22 ftIbf)
10 Nm (1.0 mkgf, 7.2 ftIbf)T.R.
10 Nm (1.0 mkgf, 7.2 ftIbf)T.R.
15 Nm (1.5 mkgf, 11 ftIbf)T.R.

CYLINDER HEAD
5-21
EAS1SL5216REMOVING THE CYLINDER HEAD
1. Remove:
• Cylinder head bolts
TIP
• Loosen the bolts in the proper sequence as
shown.
• Loosen each bolt 1/2 of a turn at a time. After
fully loosening all the bolts, remove them.
•M6  35 mm (1.38 in): “1” – “2”
• M10  149 mm (5.87 in): “3” – “6”
EAS1SL5217CHECKING THE TIMING CHAIN GUIDE (IN-
TAKE SIDE)
1. Check:
• Timing chain guide (intake side)
Damage/wear  Replace.
EAS1SL5218CHECKING THE CYLINDER HEAD
1. Eliminate:
• Combustion chamber carbon deposits
TIP
Use a rounded scraper, not a sharp instrument,
in order not to damage or scratch the spark
plug bore threads.2. Check:
• Cylinder head
Damage/scratches  Replace.
TIP
When replacing the cylinder head, replace also
the valve.
“CHECKING THE VALVE SEATS” on page
5-27.
• Cylinder head coolant passages
Mineral deposits/rust  Eliminate.
3. Measure:
• Cylinder head warpage
Out of specification  Resurface the cylin-
der head.
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a. Place a straightedge and a thickness gauge
across the cylinder head.
b. Measure the warpage.
c. If the limit is exceeded, resurface the cylin-
der head as follows.
d. Place a 400–600 grit wet sandpaper on a
surface plate, and resurface the cylinder
head using a figure-eight sanding pattern.
TIP
To ensure an even surface, turn the cylinder
head several times.
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61
2
35
4 x2 x4FWD
Warpage limit
0.05 mm (0.0020 in)

CYLINDER HEAD
5-22
EAS1SL5219INSTALLING THE CYLINDER HEAD
1. Install:
• Timing chain guide (intake side) “1”
• Dowel pin “2”
• Cylinder head gasket “3”
• Cylinder head “4”
TIP
While pulling up the timing chain, install the tim-
ing chain guide (intake side) and the cylinder
head.
2. Install:
• Washer “1”
•Bolt “2”
•Bolt “3”
TIP
Tighten the bolts using the following procedure.
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a. Wash the threads and contact surfaces of
the bolts, the contact surfaces of the wash-
ers, the contact surface of the cylinder head,
and the threads of the crankcase.
b. Apply molybdenum disulfide grease to the
threads and contact surfaces of the bolts
and to both contact surfaces of the washers
“1”.
c. Install the washers and the bolts.
d. Tighten the bolts to the specified torque in
two or three steps in the proper tightening
sequence as shown.e. Remove the bolts.
f. Again apply molybdenum disulfide grease to
the threads and contact surfaces of the bolts
and to both contact surfaces of the washers.
g. Retighten the bolts.
TIP
Tighten the bolts to the specified torque in two
or three steps in the proper tightening se-
quence as shown.
h. Put a mark on the corner “1” of the bolt (cyl-
inder head) and the cylinder head “2” as
shown.
New
12
2 4
3
1
3 22
Bolts “1”–“4”
1st
30 Nm (3.0 m·kgf, 22 ft·lbf)
Bolts “1”–“4”
2nd
20 Nm (2.0 m·kgf, 14 ft·lbf)
T R..
15
6
42
3 FWD
x2 x4
T R..
1
2

CYLINDER HEAD
5-23
i. Retighten the cylinder head mounting bolts
150° in the proper tightening sequence.
TIP
Tighten the bolts in two steps (90° and 60°) to
reach the specified angle in the proper tighten-
ing sequence.
j. Tighten the bolts to the specified torque.
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Bolts “1”–“4”
Final
Specified angle 150°
Bolt “5”, “6”
10 Nm (1.0 m·kgf, 7.2 ft·lbf)
T R..
T R..

VALVES AND VALVE SPRINGS
5-24
EAS1SL5220
VALVES AND VALVE SPRINGS
Removing the valves and valve springs
Order Part name Q’ty Remarks
Cylinder headRefer to “CYLINDER HEAD” on page 5-19.
1 Valve lifter 4
2 Adjusting pad 4
3 Valve cotter 8
4 Valve spring retainer 4
5 Valve spring 4
6 Valve stem seal 4
7 Valve spring seat 4
8 Intake valve 2
9 Exhaust valve 2
For installation, reverse the removal proce-
dure.

VALVES AND VALVE SPRINGS
5-25
EAS1SL5221REMOVING THE VALVES
TIP
Before removing the internal parts of the cylin-
der head (e.g., valves, valve springs, valve
seats), make sure that the valves are properly
sealed.
1. Remove:
• Valve lifter “1”
• Adjusting pad “2”
TIP
• Place a cloth in the timing chain space to pre-
vent adjusting pads from falling into the crank-
case.
• Make a note of the positions of valve lifters
and adjusting pads so that they can be rein-
stalled in their original places.
2. Check:
• Valve sealing
Leakage at the valve seat  Check the
valve face, the valve seat, and the valve seat
width.
“CHECKING THE VALVE SEATS” on page
5-27.
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a. Pour a clean solvent “a” into the intake and
exhaust ports.b. Check that the valves are properly sealed.
TIP
Check that there are no kerosene leaks from
the valve seat “1”.
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3. Remove:
• Valve cotter “1”
TIP
Remove the valve cotters by compressing the
valve spring with the valve spring compressor
“2” and the valve spring compressor adapter
“3”.
4. Remove:
• Valve spring retainer “1”
• Valve spring “2”
•Valve “3”
• Valve stem seal “4”
• Valve spring seat “5”
TIP
Identify the position of each part very carefully
so that it can be reinstalled in its original place. Valve lapper
90890-04101
Valve lapping tool
YM-A8998
1
2Valve spring compressor
90890-04019
YM-04019
Valve spring compressor adapter
22 mm
90890-04108
YM-04108
a1
a