2010 YAMAHA YZ450F Owners Manual

4-8
RADIATOR
11 Pipe 1/O-ring 1/1 Order Part name Q'ty Remarks

4-9
RADIATOR
HANDLING NOTE
Do not remove the radiator cap
when the engine and radiator are
hot. Scalding hot fluid and steam
may be blown out under pressure,
which could cause serious injury.
When the engine has cooled, open
the radiator cap by the following
procedure:
Place a thick rag, like a towel, over
the radiator cap, slowly rotate the
cap counterclockwise to the de-
tent. This procedure allows any re-
sidual pressure to escape. When
the hissing sound has stopped,
press down on the cap while turn-
ing counterclockwise and remove
it.
CHECKING THE RADIATOR
1. Inspect:
• Radiator core "1"
Obstruction→Blow out with com-
pressed air through rear of the ra-
diator.
Bent fin→Repair/replace.
INSTALLING THE RADIATOR
1. Install:
• O-ring "1"
• Pipe 1 "2"
• Radiator hose 1 "3"
• O-ring "4"
• Pipe 2 "5"
• Radiator hose 3 "6"• Radiator hose 4 "7"
2. Install:
• Grommet "1"
Face the smaller portion "a" of the
grommet inward.
3. Install:
• Radiator hose 2 "1"
• Left radiator "2"
4. Install:
• Radiator breather hose "1"
• Right radiator "2"
Refer to "CABLE ROUTING DIA-
GRAM" section in the CHAPTER
2.5. Install:
• Radiator guard "1"
First fit the inner hook portion "a" and
then the outer one "b" onto the radia-
tor.
6. Install:
• Bolt (radiator guard) "1"
Pipe 1:
10 Nm (1.0 m•kg, 7.2
ft•lb)
Radiator hose 1:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Pipe 2:
10 Nm (1.0 m•kg, 7.2
ft•lb)
Radiator hose 3:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Radiator hose 4:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Radiator hose 2:
2 Nm (0.2 m•kg, 1.4
ft•lb)
Left radiator:
10 Nm (1.0 m•kg, 7.2
ft•lb)
Right radiator:
10 Nm (1.0 m•kg, 7.2
ft•lb)
Bolt (radiator guard) "1":
10 Nm (1.0 m•kg, 7.2
ft•lb)

4-10
CAMSHAFTS
CAMSHAFTS
REMOVING THE CYLINDER HEAD COVER
Order Part name Q'ty Remarks
Seat Refer to "SEAT AND SIDE COVERS" sec-
tion.
Fuel tank Refer to "FUEL TANK" section in the CHAP-
TER 6.
CoverRefer to "THROTTLE BODY" section in the
CHAPTER 6.
1 Spark plug 1
2 Cylinder head breather hose 1
3 Bolt (cylinder head cover) 3
4 Cylinder head cover 1
5 Cylinder head cover gasket 1
6 Timing chain guide (top side) 1

4-11
CAMSHAFTS
REMOVING THE CAMSHAFTS
Order Part name Q'ty Remarks
1 Timing mark accessing screw1 Refer to removal section.
2 Crankshaft end accessing screw 1 Refer to removal section.
3 Timing chain tensioner cap bolt 1 Refer to removal section.
4 Timing chain tensioner 1 Refer to removal section.
5 Gasket 1 Refer to removal section.
6 Bolt (camshaft cap) 8 Refer to removal section.
7 Camshaft cap 2 Refer to removal section.
8 Clip 2 Refer to removal section.
9 Exhaust camshaft 1 Refer to removal section.
10 Intake camshaft 1 Refer to removal section.

4-12
CAMSHAFTS
REMOVING THE CAMSHAFT
1. Remove:
• Timing mark accessing screw "1"
• Crankshaft end accessing screw
"2"
2. Align:
• Alignment mark
Checking steps:
a. Turn the crankshaft counterclock-
wise with a wrench.
b. Align the alignment mark "a" on
the rotor with the alignment mark
"b" on the crankcase cover.
Make sure that the alignment mark
"c" on the exhaust camshaft sprocket
and the alignment mark "d" on the in-
take camshaft sprocket are aligned
with the edge of the cylinder head.
3. Remove:
• Timing chain tensioner cap bolt
"1"
• Timing chain tensioner "2"
• Gasket4. Remove:
• Bolt (camshaft cap) "1"
• Camshaft cap "2"
• Clip
Remove the bolts (camshaft cap) in a
crisscross pattern, working from the
outside in.
The bolts (camshaft cap) must be
removed evenly to prevent dam-
age to the cylinder head, cam-
shafts or camshaft caps.
5. Remove:
• Exhaust camshaft "1"
• Intake camshaft "2"
Attach a wire "3" to the timing chain to
prevent it from falling into the crank-
case.
CHECKING THE CAMSHAFT
1. Inspect:
• Cam lobe
Pitting/scratches/blue discolor-
ation → Replace.
2. Measure:
• Cam lobe length "a" and "b"
Out of specification → Replace.3. Measure:
• Runout (camshaft)
Out of specification → Replace.
Cam lobes length:
Intake "a":
37.750–37.850 mm
(1.4862–1.4902 in)
:
37.650 mm (1.4823 in)
Intake "b":
28.129–28.229 mm
(1.1072–1.1114 in)
:
28.029 mm (1.1035 in)
Exhaust "a":
33.540–33.640 mm
(1.3205–1.3244 in)
:
33.440 mm (1.3165 in)
Exhaust "b":
24.769–24.869 mm
(0.9752–0.9791 in)
:
24.669 mm (0.9712 in)
Runout (camshaft):
Less than 0.03 mm
(0.0012 in)

4-13
CAMSHAFTS
4. Measure:• Camshaft-to-cap clearanceOut of specification → Measure
camshaft outside diameter.
Measurement steps:
a. Install the camshaft onto the cylin- der head.
b. Position a strip of Plastigauge
®
"1" onto the camshaft.
c. Install the clip, dowel pins and camshaft caps.
• Tighten the bolts (camshaft cap) in a crisscross pattern from innermost
to outer caps.
• Do not turn the camshaft when
measuring clearance with the
Plastigauge
®.
d. Remove the camshaft caps and measure the width of the Plasti-
gauge
® "1".
5. Measure:• Camshaft outside diameter "a"
Out of specification → Replace
the camshaft.
Within specification → Replace
camshaft case and camshaft
caps as a set. CHECKING THE CAMSHAFT
SPROCKET
1. Inspect:
• Camshaft sprocket "1"Wear/damage →Replace the
camshaft assemb ly and timing
chain as a set.
CHECKING THE
DECOMPRESSION SYSTEM
1. Check: • Decompression system
Checking steps:
a. Check that the decompression
mechanism cam "1" moves
smoothly.
b. Check that the decompression
mechanism cam lever pin "2" proj-
ects from the camshaft.
CHECKING THE TIMING CHAIN
TENSIONER
1. Check:• While pressing the tensioner rod lightly with fingers, use a thin
screwdriver "1" and wind the ten-
sioner 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 as- sembly. INSTALLING THE CAMSHAFT
1. Install:
• Exhaust camshaft "1"
• Intake camshaft "2"
Installation steps:
a. Turn the crankshaft counterclock- wise with a wrench.
• Apply the molybdenum disulfide oil on the camshafts.
• Apply the engine oil on the decom- pression system.
• Fill the cylinder head with engine oil
up to the tops "a" of the valve lifters.
b. Align the alignment mark "a" on the rotor with the alignment mark
"b" on the crankcase cover.
The alignment mark "a" on the ro-
tor is there for camshaft installa-
tion. This alignment mark is
stamped 23° ATDC.
Camshaft-to-cap clear-
ance:
0.028–0.062 mm
(0.0011–0.0024 in)
:0.08 mm (0.003
in)
Bolt (camshaft cap): 10 Nm (1.0 m•kg, 7.2
ft•lb)
Camshaft outside diame-
ter: 21.959–21.972 mm
(0.8645–0.8650 in)

4-14
CAMSHAFTS
c. Fit the timing chain "3" onto both camshaft sprockets and install the
camshafts on the cylinder head.
Make sure that the alignment mark
"c" on the exhaust camshaft sprocket
and the alignment mark "d" on the in-
take camshaft sprocket are aligned
with the edge of the cylinder head.
Do not turn the crankshaft during
the camshaft insta llation. Damage
or improper valve timing will re-
sult.
d. Install the clips, camshaft caps "4"
and bolts (camshaft cap) "5".
• Before installing the clips, cover the cylinder head with a clean rag to
prevent the clips from into the cylin-
der head cavity.
• Tighten the bolts to the specified
torque in two or three steps in the
proper tightening sequence as
shown.
The bolts (camshaft cap) must be
tightened evenly, or damage to the
cylinder head, camshaft caps, and
camshaft will result.
2. Install:• Timing chain tensioner
Installation steps:
a. While pressing the tensioner rod lightly with fingers, use a thin
screwdriver and wind the tension-
er rod up fully clockwise.
b. With the rod fully wound and the chain tensioner UP mark "a" fac-
ing upward, install the gasket "1",
the timing chain tensioner "2", and
the gasket "3", and tighten the bolt
"4" to the specified torque.
c. Release the screwdriver, check the tensioner rod to come out and
tighten the gasket "5" and the cap
bolt "6" to the specified torque.
3. Turn:• Crankshaft
Counterclockwise several turns.
4. Check: • Alignment mark
Align with the crankcase align
mark.
• Camshaft match marks
Align with the cylinder head sur-
face.
Out of alignment →Adjust.
Bolt (camshaft cap):
10 Nm (1.0 m•kg, 7.2
ft•lb)
Bolt (timing chain ten-
sioner):10 Nm (1.0 m•kg, 7.2
ft•lb)
Tensioner cap bolt: 7 Nm (0.7 m•kg, 5.1
ft•lb)

4-15
CYLINDER HEAD
CYLINDER HEAD
REMOVING THE CYLINDER HEAD
Order Part name Q'ty Remarks
SeatRefer to "SEAT AND SIDE COVERS" sec-
tion.
Fuel tank Refer to "FUEL TANK" section in the CHAP-
TER 6.
Exhaust pipe and silencerRefer to "EXHAUST PIPE AND SILENCER"
section.
Radiator Refer to "RADIATOR" section
Throttle body Refer to "THROTTLE BODY" section in the
CHAPTER 6.
Camshaft Refer to "CAMSHAFTS" section.