light YAMAHA YZ450F 2010 User Guide

3-24
ELECTRICAL
ELECTRICAL
CHECKING THE SPARK PLUG
1. Remove:
• Spark plug
2. Inspect:
• Electrode "1"
Wear/damage→Replace.
• Insulator color "2"
Normal condition is a medium to
light tan color.
Distinctly different color→Check
the engine condition.
An extended run at low speeds
causes the insulator to be colored
black even if the air-fuel mixture is
normal.
3. Measure:
• Plug gap "a"
Use a wire gauge or thickness
gauge.
Out of specification→Regap.
4. Clean the plug with a spark plug
cleaner if necessary.
5. Tighten:
• Spark plug
• Before installing a spark plug, clean
the gasket surface and plug sur-
face.
• Finger-tighten "a" the spark plug
before torquing to specification "b".
CHECKING THE IGNITION TIMING
1. Remove:
• Timing mark accessing screw "1"
2. Attach:
• Timing light
• Digital tachometer
To the ignition coil lead (orange
lead "1").
3. Adjust:
• Engine idling speed
Refer to "ADJUSTING THE EN-
GINE IDLING SPEED" section.
4. Check:
• Ignition timing
Visually check the stationary
pointer "a" is within the firing
range "b" on the rotor.
Incorrect firing range→Check ro-
tor and Crankshaft position sen-
sor.
5. Install:
• Timing mark accessing screw Spark plug gap:
0.7–0.8 mm
(0.028–0.031 in)
Spark plug:
13 Nm (1.3 m•kg, 9.4
ft•lb)
Timing light:
YM-33277-A/90890-
03141
Timing mark accessing
screw:
6 Nm (0.6 m•kg, 4.3
ft•lb)

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)

4-21
VALVES AND VALVE SPRINGS
4. Measure:
• Margin thickness "a"
Out of specification → Replace.
5. Measure:
• Runout (valve stem)
Out of specification → Replace.
• When installing a new valve always
replace the guide.
• If the valve is removed or replaced
always replace the oil seal.
6. Eliminate:
• Carbon deposits
(from the valve face and valve
seat)
7. Inspect:
• Valve seat
Pitting/wear → Reface the valve
seat.
8. Measure:
• Valve seat width "a"
Out of specification → Reface the
valve seat.
Measurement steps:
a. Apply Mechanic's blueing dye
(Dykem) "b" to the valve face.
b. Install the valve into the cylinder
head.
c. Press the valve through the valve
guide and onto the valve seat to
make a clear pattern.
d. Measure the valve seat width.
Where the valve seat and valve
face made contact, blueing will
have been removed.
e. If the valve seat is too wide, too
narrow, or the seat is not cen-
tered, the valve seat must be
refaced.
9. Lap:
• Valve face
• Valve seat
This model uses titanium intake
and exhaust valves. Titanium
valves that have been used to lap
the valve seats must not be used.
Always replace lapped valves with
new valves.
• When replacing the cylinder head,
replace the valves without lapping
the valve seats and valve faces.
• When replacing the valves or valve
guides, use new valves to lap the
valve seats, and then replace them
with new valves.
Lapping steps:
a. Apply a coarse lapping compound
to the valve face.
Do not let the compound enter the
gap between the valve stem and
the guide.
b. Apply molybdenum disulfide oil to
the valve stem.
c. Install the valve into the cylinder
head.
d. Turn the valve until the valve face
and valve seat are evenly pol-
ished, then clean off all of the
compound.
For best lapping results, lightly tap
the valve seat while rotating the valve
back and forth between your hands.
e. Apply a fine lapping compound to
the valve face and repeat the
above steps.
After every lapping operation be sure
to clean off all of the compound from
the valve face and valve seat.
f. Apply Mechanic's blueing dye
(Dykem) to the valve face.
g. Install the valve into the cylinder
head.
h. Press the valve through the valve
guide and onto the valve seat to
make a clear pattern.
i. Measure the valve seat width
again. If the valve seat width is out
of specification, reface and relap
the valve seat.
Margin thickness:
Intake:
1.3 mm (0.051 in)
Exhaust:
1.0 mm (0.039 in)
Runout limit:
0.01 mm (0.0004 in)
Valve seat width:
Intake:
0.9–1.1 mm
(0.0354–0.0433 in)
:1.6 mm
(0.0630 in)
Exhaust:
0.9–1.1 mm
(0.0354–0.0433 in)
:1.6 mm
(0.0630 in)

4-22
VALVES AND VALVE SPRINGS
CHECKING THE VALVE SPRINGS
1. Measure:
• Valve spring free length "a"
Out of specification → Replace.
2. Measure:
• Compressed spring force "a"
Out of specification → Replace.
b. Installed length
3. Measure:
• Spring tilt "a"
Out of specification → Replace.CHECKING THE VALVE LIFTERS
1. Inspect:
• Valve lifter
Scratches/damage→Replace
both lifters and cylinder head.
INSTALLING THE VALVES
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"
• Install the valve "a" with the identifi-
cation 33DI on the intake side and
the valve "b" with the identification
33DE on the exhaust side.
• Install the valve springs with the
larger pitch "d" facing upward.
e. Smaller pitch3. Install:
• Valve cotters
Install the valve cotters by compress-
ing the valve spring with the valve
spring compressor "1" and the valve
spring compressor attachment "2".
4. To secure the valve cotters onto
the valve stem, lightly tap the
valve tip with a piece of wood.
Hitting the valve tip with excessive
force could damage the valve.
5. Install:
• Adjusting pad "1"
• Valve lifter "2"
• Apply the molybdenum disulfide oil
on the valve stem end.
• Apply the engine oil on the valve lift-
ers.
• Valve lifter must turn smoothly
when rotated with a finger.
• Be careful to reinstall valve lifters
and pads in their original place.
Free length (valve
spring):
Intake:
40.76 mm (1.60 in)
: 39.76 mm
(1.57 in)
Exhaust:
37.01 mm (1.46 in)
: 36.01 mm
(1.42 in)
Compressed spring
force:
Intake:
178–204 N at 34.78
mm (18.2–20.8 kg at
34.78 mm,
40.01–45.86 lb at 1.37
in)
Exhaust:
124–142 N at 30.83
mm (12.6–14.5 kg at
30.83 mm,
27.88–31.92 lb at 1.21
in)
Spring tilt limit:
Intake:
2.5°/1.8 mm (0.070 in)
Exhaust:
2.5°/1.6 mm (0.062 in)
Valve spring compres-
sor:
YM-04019/90890-04019
Valve spring compressor
attachment:
YM-04108/90890-04108

4-55
CRANKCASE AND CRANKSHAFT
DISASSEMBLING THE
CRANKCASE
1. Separate:
• Right crankcase
• Left crankcase
Separation steps:
a. Remove the crankcase bolts,
hose guide and clutch cable hold-
er.
Loosen each bolt 1/4 of a turn at a
time and after all the bolts are loos-
ened, remove them.
b. Remove the right crankcase "1".
• Place the crankcase with its left
side downward and split it by insert-
ing a screwdriver tip into the split-
ting slit "a" in the crankcase.
• Lift the right crankcase horizontally
while lightly patting the case split-
ting slit and engine mounting boss
using a soft hammer, and leave the
crankshaft and transmission with
the left crankcase.
Use soft hammer to tap on the
case half. Tap only on reinforced
portions of case. Do not tap on
gasket mating surface. Work slow-
ly and carefully. Make sure the
case halves separate evenly. If the
cases do not separate, check for a
remaining case bolt or fitting. Do
not force.
c. Remove the dowel pins and O-
ring.
REMOVING THE BALANCER
SHAFT
1. Remove:
• Balancer shaft "1"
Remove the balancer shaft with its
flat side "a" facing the crankshaft.
REMOVING THE CRANKSHAFT
1. Remove:
• Crankshaft "1"
Use the crankcase separating
tool "2".
• Install the crankcase separating
tool as shown.
• Do not use a hammer to drive out
the crankshaft.
REMOVING THE CRANKCASE
BEARING
1. Remove:
• Bearing "1"
• Remove the bearing from the
crankcase by pressing its inner
race.
• Do not use the removed bearing.
CHECKING THE TIMING CHAIN
AND TIMING CHAIN GUIDE
1. Inspect:
• Timing chain
Cracks/stiff→Replace the timing
chain and camshaft sprocket as a
set.
2. Inspect:
• Timing chain guide
Wear/damage→Replace.
CHECKING THE CRANKCASE
1. Inspect:
• Contacting surface "a"
Scratches → Replace.
• Engine mounting boss "b", crank-
case
Cracks/damage → Replace.
2. Inspect:
• Bearing
Rotate inner race with a finger.
Rough spot/seizure → Replace.
Crankcase separating
tool:
YU-A9642/90890-04152

4-57
CRANKCASE AND CRANKSHAFT
3. Install:
• Oil strainer "1"
• Bolt (oil strainer) "2"
4. Apply:
• Sealant
On the right crankcase.
Clean the contacting surface of left
and right crankcase before applying
the sealant.
5. Install:
• Dowel pin "1"
• Right crankcase
To left crankcase.
• Fit the right crankcase onto the left
crankcase. Tap lightly on the case
with soft hammer.
• When installing the crankcase, the
connecting rod should be posi-
tioned at TDC (top dead center).
6. Tighten:
• Bolt (crankcase)
Tighten the crankcase tightening
bolts in stage, using a crisscross pat-
tern.
7. Install:
• Timing chain
• Timing chain guide (exhaust side)
• Bolt for timing chain guide (ex-
haust side))
8. Remove:
• Sealant
Forced out on the cylinder mating
surface.
9. Apply:
• Engine oil
To the crank pin, bearing and oil
delivery hole.
10. Check:
• Crankshaft and transmission op-
eration.
Unsmooth operation→Repair. Bolt (oil strainer):
10 Nm (1.0 m•kg, 7.2
ft•lb)
YAMAHA Bond No. 1215
(ThreeBond® No.1215):
90890-85505
Bolt (crankcase):
12 Nm (1.2 m•kg, 8.7
ft•lb)
Bolt for timing chain
guide (exhaust side):
10 Nm (1.0 m•kg, 7.2
ft•lb)

4-59
TRANSMISSION, SHIFT CAM AND SHIFT FORK
REMOVING THE TRANSMISSION
1. Remove:
• Main axle "1"
• Drive axle "2"
• Shift cam
• Shift fork 3
• Shift fork 2
• Shift fork 1
• Remove assembly with the collar
"3" installed to the crankcase.
• Remove assembly carefully. Note
the position of each part. Pay partic-
ular attention to the location and di-
rection of shift forks.
• Remove the main axle, drive axle,
shift cam and shift fork all together
by tapping lightly on the transmis-
sion drive axle with a soft hammer.
CHECKING THE GEARS
1. Inspect:
• Matching dog "a"
• Gear teeth "b"
• Shift fork groove "c"
Wear/damage→Replace.
2. Inspect:
• O-ring "1"
Damage→Replace.
3. Check:
• Gears movement
Unsmooth movement→Repair or
replace.CHECKING THE BEARING
1. Inspect:
•Bearing "1"
Rotate inner race with a finger.
Rough spot/seizure→Replace.
CHECKING THE SHIFT FORK,
SHIFT CAM AND SEGMENT
1. Inspect:
• Shift fork "1"
Wear/damage/scratches→Re-
place.
2. Inspect:
• Shift cam "1"
• Segment "2"
Wear/damage→Replace.
3. Check:
• Shift fork movement
Unsmooth operation→Replace
shift fork.
For a malfunctioning shift fork, re-
place not only the shift fork itself but
the two gears each adjacent to the
shift fork.
INSTALLING THE TRANSMISSION
1. Install:
• 5th pinion gear (21T) "1"
• 3rd pinion gear (18T) "2"
•Collar "3"
• 4th pinion gear (22T) "4"
• 2nd pinion gear (15T) "5"
To main axle "6".
Apply the molybdenum disulfide oil
on the inner and end surface of the
idler gear and on the inner surface of
the sliding gear, then install.
2. Install:
•Collar "1"
• 2nd wheel gear (23T) "2"
• 4th wheel gear (24T) "3"
• 3rd wheel gear (23T) "4"
• 5th wheel gear (20T) "5"
•Collar "6"
• 1st wheel gear (27T) "7"
• O-ring "8"
To drive axle "9".
• Apply the molybdenum disulfide oil
on the inner and end surface of the
idler gear and on the inner surface
of the sliding gear, then install.
• Apply the lithium soap base grease
on the O-ring.

5-13
FRONT BRAKE AND REAR BRAKE
INSTALLING THE FRONT BRAKE
MASTER CYLINDER
1. Install:
• Brake master cylinder "1"
• Brake master cylinder bracket "2"
• Bolt (brake master cylinder brack-
et) "3"
• Install the bracket so that the arrow
mark "a" face upward.
• First tighten the bolts on the upper
side of the brake master cylinder
bracket, and then tighten the bolts
on the lower side.
2. Install:
• Brake lever "1"
• Bolt (brake lever) "2"
• Nut (brake lever) "3"
Apply the silicone grease on the
brake lever sliding surface, bolt and
tip of the push rod.
INSTALLING THE REAR BRAKE
MASTER CYLINDER
1. Install:
• Copper washer "1"
• Brake hose "2"
• Union bolt "3"
Always use new copper washers.
Install the brake hose so that its
pipe portion "a" directs as shown
and lightly touches the projection
"b" on the brake master cylinder.
2. Install:
• Brake master cylinder "1"
• Bolt (brake master cylinder) "2"3. Install:
• Spring "1"
• Brake pedal "2"
• O-ring "3"
• Bolt (brake pedal) "4"
• Clip "5"
Apply the lithium soap base grease
on the bolt, O-ring and brake pedal
bracket.
4. Install:
•Pin "1"
• Washer "2"
• Cotter pin "3"
After installing, check the brake pedal
height. Refer to "ADJUSTING THE
REAR BRAKE" section in the CHAP-
TER 3.
INSTALLING THE FRONT BRAKE
HOSE
1. Install:
• Copper washer "1"
• Brake hose "2"
• Union bolt "3"
Always use new copper washers.
Bolt (brake master cylin-
der bracket):
9 Nm (0.9 m•kg, 6.5
ft•lb)
Bolt (brake lever):
6 Nm (0.6 m•kg, 4.3
ft•lb)
Nut (brake lever):
6 Nm (0.6 m•kg, 4.3
ft•lb)
Union bolt:
30 Nm (3.0 m•kg, 22
ft•lb)
Bolt (brake master cylin-
der):
10 Nm (1.0 m•kg, 7.2
ft•lb)
Bolt (brake pedal):
26 Nm (2.6 m•kg, 19
ft•lb)
Union bolt:
30 Nm (3.0 m•kg, 22
ft•lb)

5-14
FRONT BRAKE AND REAR BRAKE
Install the brake hose so that its
pipe portion "a" directs as shown
and lightly touches the projection
"b" on the brake caliper.
2. Install:
• Brake hose holder "1"
• Bolt (brake hose holder) "2"
Align the top "a" of the brake hose
holder with the paint "b" of the brake
hose.
3. Pass the brake hose through the
cable guide "1".
4. Install:
• Copper washer "1"
• Brake hose "2"
• Union bolt "3"
Always use new copper washers.
Install the brake hose so that its
pipe portion "a" directs as shown
and lightly touches the projection
"b" on the brake master cylinder.
INSTALLING THE REAR BRAKE
HOSE
1. Install:
• Copper washer "1"
• Brake hose "2"
• Union bolt "3"
Always use new copper washers.
Install the brake hose so that its
pipe portion "a" directs as shown
and lightly touches the projection
"b" on the brake caliper.
2. Install:
• Brake hose holder "1"
• Screw (brake hose holder) "2"
After installing the brake hose
holders, make sure the brake hose
does not contact the spring (rear
shock absorber). If it does, correct
its twist.
FILLING THE BRAKE FLUID
1. Fill:
• Brake fluid
Until the fluid level reaches
"LOWER" level line "a".
• Use only the designated quality
brake fluid:
otherwise, the rubber seals may
deteriorate, causing leakage and
poor brake performance.
• Refill with the same type of brake
fluid;
mixing fluids may result in a
harmful chemical reaction and
lead to poor performance.
• Be careful that water does not
enter the master cylinder when
refilling. Water will significantly
lower the boiling point of the flu-
id and may result in vapor lock.
Bolt (brake hose holder):
8 Nm (0.8 m•kg, 5.8 ft
•lb)
Union bolt:
30 Nm (3.0 m•kg, 22
ft•lb)
Union bolt:
30 Nm (3.0 m•kg, 22
ft•lb)
Screw (brake hose hold-
er):
3 Nm (0.3 m•kg, 2.2
ft•lb)
Recommended brake flu-
id:
DOT #4