engine YAMAHA YZ450F 2012 User Guide

1-18
STARTING AND BREAK-IN
• Unlike a two-stroke engine, this
engine cannot be kick started
when the throttle is open be-
cause the kickstarter may kick
back. Also, if the throttle is open
the air/fuel mixture may be too
lean for the engine to start.
• Before starting the machine, per-
form the checks in the pre-opera-
tion check list.
AIR FILTER MAINTENANCE
According to "CLEANING THE AIR
FILTER ELEMENT" section in the
CHAPTER 3, apply the foam-air-filter
oil or its equivalent to the element.
(Excess oil in the element may ad-
versely affect engine starting.)
STARTING A COLD ENGINE
1. Inspect the coolant level.
2. Shift the transmission into neutral.
3. Pull the starter knob/ idle screw
"1" to its full length.
Use the starter knob/ idle screw be-
low an air temperature of 15°C
(59°F).
4. Push the kickstarter down lightly
with your foot until resistance is
felt.
5. With the throttle fully closed, fold
out the kickstarter lever, move it
down lightly with your foot until the
gears engage, and then push it
down smoothly but forcefully.
Do not open the throttle while kick-
ing the kickstarter crank. Other-
wise, the kickstarter crank may
kick back.
If the engine fails to start, give the
kickstarter 10 to 20 slow kicks at full
throttle in order to clear the engine of
the rich air-fuel mixture retained in it.
6. When the engine starts running,
warm it up one or two minutes at
a steady speed (of 3,000 to 5,000
r/min), and then return the starter
knob/ idle screw to its original po-
sition.
7. Push the engine stop switch "1".
Do not warm up the engine for ex-
tended periods of time.
STARTING A WARM ENGINE
To start a warm engine, make sure
that the starter (choke) knob/idling
screw is pushed in and the throttle is
closed, and then start the engine by
pushing the kickstarter.
If the engine fails to start, give the
kickstarter 10 to 20 slow kicks at full
throttle in order to clear the engine of
the rich air-fuel mixture retained in it.
BREAK-IN PROCEDURES
1. Before starting the engine, fill the
fuel tank with the fuel.
2. Perform the pre-operation checks
on the machine.
3. Start and warm up the engine.
Check the idle speed, and check
the operation of the controls and
the engine stop switch. Then, re-
start the engine and check its op-
eration within no more than 5
minutes after it is restarted.
4. Operate the machine in the lower
gears at moderate throttle open-
ings for five to eight minutes.
5. Check how the engine runs when
the machine is ridden with the
throttle 1/4 to 1/2 open (low to me-
dium speed) for about one hour.6. Restart the engine and check the
operation of the machine through-
out its entire operating range. Re-
start the machine and operate it
for about 10 to 15 more minutes.
The machine will now be ready to
race.
• After the break-in or before each
race, you must check the entire
machine for loose fittings and
fasteners as per "TORQUE-
CHECK POINTS". Tighten all
such fasteners as required.
• When any of the following parts
have been replaced, they must
be broken in.
CYLINDER AND CRANKSHAFT:
About one hour of break-in oper-
ation is necessary.
PISTON, RING, VALVES, CAM-
SHAFTS AND GEARS:
These parts require about 30
minutes of break-in operation at
half-throttle or less. Observe the
condition of the engine carefully
during operation.

1-19
TORQUE-CHECK POINTS
TORQUE-CHECK POINTS
Concerning the tightening torque, refer to "TIGHTENING TORQUES" section in the CHAPTER 2.
Frame construction Frame to rear frame
Combined seat and fuel tank Fuel tank to frame
Exhaust system Silencer to rear frame
Engine mounting Frame to engine
Engine bracket to engine
Engine bracket to frame
Steering Steering stem to handlebar Steering stem to frame
Steering stem to upper bracket
Upper bracket to handlebar
Suspension Front Steering stem to front fork Front fork to upper bracket
Front fork to lower bracket
Rear For link type Assembly of links
Link to frame
Link to rear shock absorber
Link to swingarm
Installation of rear shock absorber Rear shock absorber to frame
Installation of swingarm Tightening of pivot shaft
Wheel Installation of wheel Front Tightening of wheel axle
Tightening of axle holder
Rear Tightening of wheel axle
Wheel to rear wheel sprocket
Brake Front Brake caliper to front fork
Brake disc to wheel
Tightening of union bolt
Brake master cylinder to handlebar
Tightening of bleed screw
Tightening of brake hose holder
Rear Brake pedal to frame
Brake disc to wheel
Tightening of union bolt
Brake master cylinder to frame
Tightening of bleed screw
Tightening of brake hose holder
Fuel system Fuel pump to fuel tank

1-20
CLEANING AND STORAGE
CLEANING AND STORAGE
CLEANING
Frequent cleaning of your machine
will enhance its appearance, maintain
good overall performance, and ex-
tend the life of many components.
1. Before washing the machine,
block off the end of the exhaust
pipe to prevent water from enter-
ing. A plastic bag secured with a
rubber band may be used for this
purpose.
2. If the engine is excessively
greasy, apply some degreaser to
it with a paint brush. Do not apply
degreaser to the chain, sprockets,
or wheel axles.
3. Rinse the dirt and degreaser off
with a garden hose; use only
enough pressure to do the job.
Do not use high-pressure washers
or steam-jet cleaners since they
cause water seepage and deterio-
ration seals.
4. After the majority of the dirt has
been hosed off, wash all surfaces
with warm water and a mild deter-
gent. Use an old toothbrush to
clean hard-to-reach places.
5. Rinse the machine off immediate-
ly with clean water, and dry all
surfaces with a soft towel or cloth.
6. Immediately after washing, re-
move excess water from the
chain with a paper towel and lubri-
cate the chain to prevent rust.
7. Clean the seat with a vinyl uphol-
stery cleaner to keep the cover
pliable and glossy.
8. Automotive wax may be applied
to all painted or chromed surfac-
es. Avoid combination cleaner-
waxes, as they may contain abra-
sives.
9. After completing the above, start
the engine and allow it to idle for
several minutes.STORAGE
If your machine is to be stored for 60
days or more, some preventive mea-
sures must be taken to avoid deterio-
ration. After cleaning the machine
thoroughly, prepare it for storage as
follows:
1. Fill up the fuel tank and add fuel
stabilizer (if available) to prevent
the fuel tank from rusting and the
fuel from deteriorating.
2. Remove the spark plug, pour a ta-
blespoon of SAE 10W-40 motor
oil in the spark plug hole, and re-
install the plug. With the engine
stop switch pushed in, kick the en-
gine over several times to coat the
cylinder walls with oil.
3. Remove the drive chain, clean it
thoroughly with solvent, and lubri-
cate it. Reinstall the chain or store
it in a plastic bag tied to the frame.
4. Lubricate all control cables.
5. Block the frame up to raise the
wheels off the ground.
6. Tie a plastic bag over the exhaust
pipe outlet to prevent moisture
from entering.
7. If the machine is to be stored in a
humid or salt-air environment,
coat all exposed metal surfaces
with a film of light oil. Do not apply
oil to rubber parts or the seat cov-
er.
Make any necessary repairs before
the machine is stored.

2-1
GENERAL SPECIFICATIONS
SPECIFICATIONS
GENERAL SPECIFICATIONS
Model name: YZ450FB (USA, CDN, AUS, NZ)
YZ450F (EUROPE, ZA)
Model code number: 33D9 (USA,CDN)
33DA (EUROPE)
33DC (AUS, NZ, ZA)
Dimensions: USA, CDN EUROPE AUS, NZ, ZA
Overall length 2,195 mm (86.42
in)2,191 mm (86.26
in)2,196 mm (86.46
in)
Overall width 825 mm (32.48 in)←←
Overall height 1,312 mm (51.65
in)1,311 mm (51.61
in)1,312 mm (51.65
in)
Seat height 999 mm (39.33 in)←998 mm (39.29 in)
Wheelbase 1,492 mm (58.74
in)1,487 mm (58.54
in)←
Minimum ground clearance 384 mm (15.12 in) 383 mm (15.08 in)←
Weight:
Curb weight 111 kg (245 lb)
Engine:
Engine type Liquid cooled 4-stroke, DOHC
Cylinder arrangement Single cylinder
Displacement 449.7 cm
3 (15.8 Imp oz, 15.2 US oz)
Bore × stroke 97.0 × 60.8 mm (3.82 × 2.39 in)
Compression ratio 12.5 : 1
Starting system Kickstarter
Lubrication system: Dry sump
Oil type or grade:
Engine oil
Recommended brand: YAMALUBE
SAE10W-30, SAE10W-40, SAE10W-50,
SAE15W-40, SAE20W-40 or SAE20W-50
API service SG type or higher,
JASO standard MA
Oil capacity:
Engine oil
Periodic oil change 0.95 L (0.84 Imp qt, 1.00 US qt)
With oil filter replacement 1.0 L (0.88 Imp qt, 1.06 US qt)
Total amount 1.2 L (1.06 Imp qt, 1.27 US qt)
Coolant capacity (including all routes): 1.13 L (0.99 Imp qt, 1.19 US qt)
Air filter: Wet type element
2

2-3
MAINTENANCE SPECIFICATIONS
MAINTENANCE SPECIFICATIONS
ENGINEWheel travel:
Front wheel travel 310 mm (12.2 in)
Rear wheel travel 315 mm (12.4 in) (For USA, CDN)
312 mm (12.3 in) (For EUROPE, AUS, NZ, ZA)
Electrical:
Ignition system TCI
Item Standard Limit
Cylinder head:
Warp limit ---- 0.05 mm (0.002
in)
Cylinder:
Bore size 97.00–97.01 mm (3.8189–3.8193 in) ----
Out of round limit ---- 0.05 mm (0.002
in)
Camshaft:
Drive method Chain drive (Left) ----
Camshaft cap inside diameter 22.000–22.021 mm (0.8661–0.8670 in) ----
Camshaft outside diameter 21.959–21.972 mm (0.8645–0.8650 in) ----
Shaft-to-cap clearance 0.028–0.062 mm (0.0011–0.0024 in) 0.08 mm (0.003
in)
Cam dimensions
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 (1.1074–1.1114 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)
Camshaft runout limit ---- 0.03 mm
(0.0012 in)

2-8
MAINTENANCE SPECIFICATIONS
Throttle position sensor:----
Throttle position sensor maximum resistance 5 kΩ----
Throttle position sensor variable resistance 0–2 kΩ (full closed) ----
Throttle position sensor input voltage 4–6 V ----
Fuel injection sensor:----
Crankshaft position sensor resistance 248–372 Ω----
Intake air pressure sensor output voltage 3.57–3.71 V at 101.3kPa (1.013 kg/cm
2,
14.41 psi)----
Atmospheric pressure sensor output voltage 3.57–3.71 V at 101.3kPa (1.013 kg/cm
2,
14.41 psi)----
Intake air temperature sensor 5.4–6.6 kΩat 0 °C (32 °F)
290–390 Ωat 80 °C (176 °F)----
Idling condition:----
Engine idle speed 1,900–2,100 r/min ----
Oil temperature 55–65 °C (131–149 °F) ----
Lubrication system:
Oil filter type Paper type ----
Oil pump type Trochoid type ----
Tip clearance 0.12 mm or less (0.0047 in or less) 0.20 mm (0.008
in)
Side clearance 0.09–0.17 mm (0.0035–0.0067 in) 0.24 mm (0.009
in)
Housing and rotor clearance 0.03–0.10 mm (0.0012–0.0039 in) 0.17 mm (0.007
in)
Bypass valve setting pressure 40–80 kPa (0.4–0.8 kg/cm
2, 5.69–11.38
psi)----
Cooling:
Radiator core size
Width 121.4 mm (4.78 in) ----
Height 235 mm (9.25 in) ----
Thickness 28 mm (1.10 in) ----
Radiator cap opening pressure 108–137 kPa (1.08–1.37 kg/cm
2,
15.4–19.5 psi)----
Radiator capacity (total) 0.62 L (0.55 Imp qt, 0.66 US qt) ----
Water pump
Type Single-suction centrifugal pump ----Item Standard Limit

2-11
TIGHTENING TORQUES
TIGHTENING TORQUES
ENGINE
△- marked portion shall be checked for torque tightening after break-in or before each race.
ItemThread
sizeQ'ty Tightening torque Remarks
Spark plug M10S 1 13 Nm (1.3 m•kg, 9.4 ft•lb)
Camshaft cap M6 8 10 Nm (1.0 m•kg, 7.2 ft•lb)
Cylinder head blind plug screw M12 2 28 Nm (2.8 m•kg, 20 ft•lb)
Oil passage plug M8 1 15 Nm (1.5 m•kg, 11 ft•lb)
Cylinder head (stud bolt) M6 3 7 Nm (0.7 m•kg, 5.1 ft•lb)
Cylinder head (bolt) M10 4 Refer to TIP.
*1
Cylinder head (bolt) M6 2 10 Nm (1.0 m•kg, 7.2 ft•lb)
Cylinder head cover M6 3 10 Nm (1.0 m•kg, 7.2 ft•lb)
Cylinder M6 1 10 Nm (1.0 m•kg, 7.2 ft•lb)
Timing chain tensioner M6 2 10 Nm (1.0 m•kg, 7.2 ft•lb)
Timing chain tensioner cap bolt M6 1 7 Nm (0.7 m•kg, 5.1 ft•lb)
Timing chain guide stopper plate (exhaust
side)M6 2 10 Nm (1.0 m•kg, 7.2 ft•lb)
Exhaust pipe (nut) M6 3 10 Nm (1.0 m•kg, 7.2 ft•lb)
Exhaust pipe and frame M8 1 20 Nm (2.0 m•kg, 14 ft•lb)
△Silencer M8 2 30 Nm (3.0 m•kg, 22 ft•lb)
Silencer clamp (front) M8 1 12 Nm (1.2 m•kg, 8.7 ft•lb)
Silencer clamp (rear) M8 1 16 Nm (1.6 m•kg, 11 ft•lb)
Starter knob/Idle screw M12 1 2 Nm (0.2 m•kg, 1.4 ft•lb)
Throttle body joint M6 2 10 Nm (1.0 m•kg, 7.2 ft•lb)
Throttle body joint clamp M5 1 3 Nm (0.3 m•kg, 2.2 ft•lb)
△Air filter case M6 3 7 Nm (0.7 m•kg, 5.1 ft•lb)
Air filter joint and air filter case M4 9 1 Nm (0.1 m•kg, 0.7 ft•lb)
Air filter case cover M5 2 5 Nm (0.5 m•kg, 3.6 ft•lb)
Air filter joint clamp M4 1 4 Nm (0.4 m•kg, 2.9 ft•lb)
Throttle cable adjust bolt and locknut M6 1 4 Nm (0.4 m•kg, 2.9 ft•lb)
Throttle cable (pull) M10 1 7 Nm (0.7 m•kg, 5.1 ft•lb)
Throttle cable (return) M10 1 7 Nm (0.7 m•kg, 5.1 ft•lb)
Throttle cable cover M5 2 4 Nm (0.4 m•kg, 2.9 ft•lb)
Air duct M6 3 7 Nm (0.7 m•kg, 5.1 ft•lb)
Radiator M6 4 10 Nm (1.0 m•kg, 7.2 ft•lb)
Radiator hose clamp M6 8 2 Nm (0.2 m•kg, 1.4 ft•lb)
Radiator pipe 1 M6 1 10 Nm (1.0 m•kg, 7.2 ft•lb)
Radiator pipe 2 M6 1 10 Nm (1.0 m•kg, 7.2 ft•lb)
Impeller M8 1 14 Nm (1.4 m•kg, 10 ft•lb)
Water pump housing cover M6 4 10 Nm (1.0 m•kg, 7.2 ft•lb)
Coolant drain bolt M6 1 10 Nm (1.0 m•kg, 7.2 ft•lb)
Oil pump cover M4 1 2 Nm (0.2 m•kg, 1.4 ft•lb)
Oil pump M6 2 10 Nm (1.0 m•kg, 7.2 ft•lb)
Oil pump drive gear shaft M6 1 10 Nm (1.0 m•kg, 7.2 ft•lb)

2-14
TIGHTENING TORQUES
△Brake pedal mounting M8 1 26 Nm (2.6 m•kg, 19 ft•lb)
Brake pedal position locknut M6 1 6 Nm (0.6 m•kg, 4.3 ft•lb)
△Rear brake master cylinder and frame M6 2 10 Nm (1.0 m•kg, 7.2 ft•lb)
Rear brake master cylinder cap M4 2 2 Nm (0.2 m•kg, 1.4 ft•lb)
△Rear brake hose union bolt (brake cali-
per)M10 1 30 Nm (3.0 m•kg, 22 ft•lb)Copper
washer
△Rear brake hose union bolt (brake master
cylinder)M10 1 30 Nm (3.0 m•kg, 22 ft•lb)Copper
washer
△Rear wheel axle and axle nut M22 1 135 Nm (13.5 m•kg, 98 ft•lb)
△Driven sprocket and wheel hub M8 6 42 Nm (4.2 m•kg, 30 ft•lb)
△Nipple (spoke) — 72 3 Nm (0.3 m•kg, 2.2 ft•lb)
△Disc cover and rear brake caliper M6 2 10 Nm (1.0 m•kg, 7.2 ft•lb)
△Protector and rear brake caliper M6 2 7 Nm (0.7 m•kg, 5.1 ft•lb)
Drive chain puller adjust bolt and locknut M8 2 21 Nm (2.1 m•kg, 15 ft•lb)
Engine mounting:
△Upper engine bracket and frame M8 4 45 Nm (4.5 m•kg, 32 ft•lb)
△Front engine bracket and frame M8 4 34 Nm (3.4 m•kg, 24 ft•lb)
△Engine and engine bracket (front) M10 1 53 Nm (5.3 m•kg, 38 ft•lb)
△Engine and engine bracket (upper) M10 2 45 Nm (4.5 m•kg, 32 ft•lb)
△Engine and frame (lower) M10 1 53 Nm (5.3 m•kg, 38 ft•lb)
△Engine guard M6 1 10 Nm (1.0 m•kg, 7.2 ft•lb)
Lower engine guard M6 3 10 Nm (1.0 m•kg, 7.2 ft•lb)
△Pivot shaft and nut M16 1 85 Nm (8.5 m•kg, 61 ft•lb)
△Relay arm and swingarm M14 1 70 Nm (7 m•kg, 50 ft•lb)
△Relay arm and connecting rod M14 1 80 Nm (8.0 m•kg, 58 ft•lb)
△Connecting rod and frame M14 1 80 Nm (8.0 m•kg, 58 ft•lb)
△Rear shock absorber and frame M10 1 56 Nm (5.6 m•kg, 40 ft•lb)
△Rear shock absorber and relay arm M10 1 53 Nm (5.3 m•kg, 38 ft•lb)
△Rear shock absorber locknut M60 1 30 Nm (3.0 m•kg, 22 ft•lb)
△Rear frame and frame (upper) M8 1 32 Nm (3.2 m•kg, 23 ft•lb)
△Rear frame and frame (lower) M8 2 32 Nm (3.2 m•kg, 23 ft•lb)
△Swingarm and brake hose holder M5 4 3 Nm (0.3 m•kg, 2.2 ft•lb)
Upper drive chain tensioner M8 1 16 Nm (1.6 m•kg, 11 ft•lb)
Lower drive chain tensioner M8 1 16 Nm (1.6 m•kg, 11 ft•lb)
Drive chain support and swingarm M6 3 7 Nm (0.7 m•kg, 5.1 ft•lb)
△Seal guard and swingarm M5 3 4 Nm (0.4 m•kg, 2.9 ft•lb)
△Fuel tank (front) M6 2 9 Nm (0.9 m•kg, 6.5 ft•lb)
Fuel tank bracket (front) M6 4 7 Nm (0.7 m•kg, 5.1 ft•lb)
△Fuel tank (rear) M6 2 9 Nm (0.9 m•kg, 6.5 ft•lb)
Fuel tank bracket (rear) M6 2 7 Nm (0.7 m•kg, 5.1 ft•lb)
△Fuel pump M5 6 4 Nm (0.4 m•kg, 2.9 ft•lb)
Protector and fuel pump bracket M5 2 4 Nm (0.4 m•kg, 2.9 ft•lb)
Fuel tank side cover M6 4 7 Nm (0.7 m•kg, 5.1 ft•lb)
Fuel tank and seat set bracket M6 1 7 Nm (0.7 m•kg, 5.1 ft•lb)Item
Thread
sizeQ'ty Tightening torque Remarks

2-16
TIGHTENING TORQUES
GENERAL TORQUE
SPECIFICATIONS
This chart specifies torque for stan-
dard fasteners with standard I.S.O.
pitch threads. Torque specifications
for special components or assem-
blies are included in the applicable
sections of this book. To avoid war-
page, tighten multi-fastener assem-
blies in a crisscross fashion, in
progressive stages, until full torque is
reached. Unless otherwise specified,
torque specifications call for clean,
dry threads. Components should be
at room temperature.A. Distance between flats
B. Outside thread diameter
DEFINITION OF UNITS
A
(Nut)B
(Bolt
)TORQUE SPECIFI-
CATION
Nm m•kg ft•lb
10
mm6 mm 6 0.6 4.3
12
mm8 mm 15 1.5 11
14
mm10
mm30 3.0 22
17
mm12
mm55 5.5 40
19
mm14
mm85 8.5 61
22
mm16
mm130 13 94
Unit Read Definition Measure
mm
millimeter 10-3 meter Length
cmcentimeter 10-2 meter Length
kgkilogram 103 gram Weight
NNewton 1 kg × m/sec2Force
NmNewton meter N × m Torque
m•kgMeter kilogram m × kg Torque
PaPascal N/m2Pressure
N/mmNewton per millimeter N/mm Spring rate
LLiter — Volume or capacity
cm3Cubic centimeter — Volume or capacity
r/minRevolution per minute — Engine speed

2-21
CABLE ROUTING DIAGRAM
1. Clutch cable
2. Throttle cable (return)
3. Throttle cable (pull)
4. Cable holder
5. Clamp
6. Rectifier/regulator
7. Ignition coil
8. Ignition coil coupler
9. AC magneto coupler
10. Radiator hose 2
11. Ground lead terminal
12. Plug cap
13. Ignition coil bracket
14. Clamp (lock)
15. Clamp (clip)
16. AC magneto lead
17. ECU bracket
18. Cylinder head cover installing
boltA. Pass the clutch cable, throttle
cables, and engine stop switch
lead through the cable holder.
Pass the clutch cable through
the lower guide only.
B. Route the engine stop switch
lead to the inside of the clip.
C. Fasten the rectifier/regulator
lead and engine stop switch lead
(wire harness end).
D. Insert the projection on the en-
gine stop switch coupler into the
hole in the bracket.
E. Insert the projection on the recti-
fier/regulator coupler into the
hole in the bracket.
F. Position the ignition coil bracket
to the outside of the ignition coil,
and insert the bolts from the igni-
tion coil side.
G. Fasten the AC magneto lead to
the ignition coil bracket with a
plastic locking tie, making sure
to position the tie above the low-
er mounting portion of the brack-
et. Face the buckle of the plastic
locking tie forward, and then cut
off the excess end of the tie.
H. Route the ignition coil lead be-
tween the condenser and the ig-
nition coil.
I. Fit the clip portion of the clamp
into the ignition coil bracket and
fasten the clutch cable with the
locking portion of the clamp.
J. Route the clutch cable to the
outside of the AC magneto lead.
K. Route the throttle cables under
radiator hose 2, making sure not
to twist the cables.
L. Route the AC magneto lead to
the inside of the throttle cables
and clutch cable.
M. Install the ground lead terminal
between the ECU bracket and
the cable holder, making sure to
position the terminal between
the stoppers.
N. Push in the spark plug cap com-
pletely, making sure that there is
no gap between the cylinder
head cover and the cap.
O. Pass the high tension cord so
that it may not go right over the
cylinder head cover installing
bolt when viewed directly from
above.
P. Apply sealant to the slit and in-
ner surface of the grommet, and
then install the grommet at the
position shown.