2015 YAMAHA YZ450F Chain

CHAIN DRIVE
4-65
4. Check:
• Drive chain rollers “1”
Damage/wear  Replace the drive chain.
• Drive chain side plates “2”
Damage/wear  Replace the drive chain.
5. Lubricate:
•Drive chain
EAS1SL5193CHECKING THE DRIVE SPROCKET
1. Check:
• Drive sprocket
More than 1/4 tooth wear “a”  Replace the
drive sprocket and the rear wheel sprocket
as a set.
Bent tooth  Replace the drive sprocket
and the rear wheel sprocket as a set.
EAS1SL5194CHECKING THE REAR WHEEL SPROCKET
Refer to “CHECKING AND REPLACING THE
REAR WHEEL SPROCKET” on page 4-8.
EAS1SL5195INSTALLING THE DRIVE CHAIN
1. Install:
• Drive chain “1”
• Drive chain joint “2”
• Joint clip “3”
EWA
WARNING
When installing the joint clip, always keep
the direction as shown in the figure.2. Lubricate:
•Drive chain
3. Install:
• Drive sprocket
• Lock washer
• Drive sprocket nut
Refer to “ENGINE REMOVAL” on page 5-1.
ECA1DX1014
NOTICE
Never install a new drive chain onto worn
drive sprockets; this will dramatically short-
en the drive chain’s life.
4. Adjust:
• Drive chain slack
Refer to “ADJUSTING THE DRIVE CHAIN
SLACK” on page 3-27.
ECA13550
NOTICE
A drive chain that is too tight will overload
the engine and other vital parts, and one
that is too loose can skip and damage the
swingarm or cause an accident. Therefore,
keep the drive chain slack within the speci-
fied limits.
b. Correct
1. Drive chain roller
2. Drive sprocket
New
Drive sprocket nut
75 Nm (7.5 m·kgf, 54 ft·lbf)
Drive chain slack
50–60 mm (1.97–2.36 in)
New
T R..

CHAIN DRIVE
4-66

5
ENGINE
ENGINE REMOVAL......................................................................................... 5-1
REMOVING THE SILENCER ..................................................................... 5-6
REMOVING THE EXHAUST PIPE 2.......................................................... 5-6
REMOVING THE DRIVE SPROCKET ....................................................... 5-6
REMOVING THE ENGINE ......................................................................... 5-7
CHECKING THE SILENCER AND EXHAUST PIPE.................................. 5-7
CHANGING THE SILENCER FIBER ......................................................... 5-7
INSTALLING THE ENGINE........................................................................ 5-8
INSTALLING THE BRAKE PEDAL ............................................................ 5-9
INSTALLING THE DRIVE SPROCKET...................................................... 5-9
INSTALLING THE EXHAUST PIPE AND MUFFLER............................... 5-10
CAMSHAFT.................................................................................................... 5-11
REMOVING THE CAMSHAFT ................................................................. 5-13
CHECKING THE CAMSHAFT.................................................................. 5-14
CHECKING THE TIMING CHAIN AND CAMSHAFT SPROCKET .......... 5-15
CHECKING THE TIMING CHAIN TENSIONERS .................................... 5-15
CHECKING THE DECOMPRESSION SYSTEM...................................... 5-16
INSTALLING THE CAMSHAFTS ............................................................. 5-16
CYLINDER HEAD........................................................................................... 5-19
REMOVING THE CYLINDER HEAD........................................................ 5-21
CHECKING THE TIMING CHAIN GUIDE (INTAKE SIDE) ...................... 5-21
CHECKING THE CYLINDER HEAD ........................................................ 5-21
INSTALLING THE CYLINDER HEAD ...................................................... 5-22
VALVES AND VALVE SPRINGS................................................................... 5-24
REMOVING THE VALVES ....................................................................... 5-25
CHECKING THE VALVES AND VALVE GUIDES ................................... 5-26
CHECKING THE VALVE SEATS ............................................................. 5-27
CHECKING THE VALVE SPRINGS......................................................... 5-29
CHECKING THE VALVE LIFTERS .......................................................... 5-29
INSTALLING THE VALVES ..................................................................... 5-30
CYLINDER AND PISTON............................................................................... 5-32
REMOVING THE PISTON ....................................................................... 5-33
CHECKING THE CYLINDER AND PISTON ............................................ 5-33
CHECKING THE PISTON RINGS............................................................ 5-34
CHECKING THE PISTON PIN ................................................................. 5-35
INSTALLING THE PISTON AND CYLINDER .......................................... 5-35

AC MAGNETO................................................................................................ 5-59
REMOVING THE AC MAGNETO............................................................. 5-60
CHECKING THE AC MAGNETO ............................................................. 5-60
CHECKING THE WOODRUFF KEY ........................................................ 5-60
INSTALLING THE AC MAGNETO ........................................................... 5-60
CRANKCASE................................................................................................. 5-62
DISASSEMBLING THE CRANKCASE..................................................... 5-65
REMOVING THE CRANKCASE BEARING ............................................. 5-65
CHECKING THE TIMING CHAIN, TIMING CHAIN GUIDE,
OIL STRAINER ........................................................................................ 5-65
CHECKING THE CRANKCASE ............................................................... 5-65
ASSEMBLING THE CRANKCASE........................................................... 5-66
CRANKSHAFT ASSEMBLY AND BALANCER SHAFT............................... 5-67
REMOVING THE BALANCER SHAFT..................................................... 5-68
REMOVING THE CRANKSHAFT ASSEMBLY ........................................ 5-68
CHECKING THE CRANKSHAFT ASSEMBLY......................................... 5-68
INSTALLING THE CRANKSHAFT ASSEMBLY....................................... 5-69
TRANSMISSION............................................................................................. 5-70
REMOVING THE TRANSMISSION ......................................................... 5-71
CHECKING THE SHIFT FORKS.............................................................. 5-71
CHECKING THE SHIFT DRUM ASSEMBLY ........................................... 5-72
CHECKING THE TRANSMISSION .......................................................... 5-72
INSTALLING THE TRANSMISSION ........................................................ 5-72

ENGINE REMOVAL
5-4
Removing the engine
Order Part name Q’ty Remarks
Use a suitable stand to raise the front wheel
off the ground.
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.
Rear fender 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.
Air filter case Refer to “THROTTLE BODY” on page 7-5.
Throttle body Refer to “THROTTLE BODY” on page 7-5.
Clutch cable Refer to “CLUTCH” on page 5-37.
Shift pedal Refer to “SHIFT SHAFT” on page 5-49.
1 Engine guard 1
2 Brake pedal 1
3Spring 1
4 Cylinder head breather hose 1
5 Drive sprocket cover 1
6 Drive chain guide 1
New
New
LS
M
8
8
7
6
11
45
New
1 10
3
2

ENGINE REMOVAL
5-6
EAS1SL5198REMOVING THE SILENCER
1. Remove:
• Rear shock absorber assembly lower bolt
“1”
• Connecting arm bolt (frame side) “2”
• Silencer “3”
TIP
Move the rear shock absorber to the left side of
the chassis, and remove the silencer.
EAS1SL5199REMOVING THE EXHAUST PIPE 2
1. Remove:
• Exhaust pipe 2
TIP
Put the Exhaust pipe 2 into the state as shown
by moving this, and then remove it.
EAS1SL5200REMOVING THE DRIVE SPROCKET
1. Straighten the lock washer tab.
2. Remove:
• Nut (drive sprocket) “1”
• Lock washer “2”
TIP
Loosen the nut while applying the rear brake.
3. Remove:
• Drive sprocket “1”
• Drive chain “2”
TIP
Remove the drive sprocket together with the
drive chain.
1 2
3

ENGINE REMOVAL
5-9
EAS1SL5205INSTALLING THE BRAKE PEDAL
1. Install:
• Spring “1”
• Brake pedal “2”
• O-rings “3”
• Bolt (brake pedal) “4”
•Clip “5”
TIP
Apply the lithium soap base grease on the bolt,
O-rings and brake pedal bracket.
EAS1SL5206INSTALLING THE DRIVE SPROCKET
1. Install:
• Drive sprocket “1”
• Drive chain “2”
TIP
Install the drive sprocket together with the drive
chain.2. Install:
• Lock washer “1”
• Nut (drive sprocket) “2”
TIP
Tighten the nut while applying the rear brake.
ECA33DD040
NOTICE
Make sure to tighten to specification; other-
wise, it may damage the other part that is
fastened together.
3. Bend the lock washer tab to lock the nut.
4. Install:
• Drive sprocket guide
• Drive sprocket cover “1”
• Bolt (drive sprocket cover) “2” Bolt (brake pedal)
26 Nm (2.6 m·kgf, 19 ft·lbf)
M
78
9
9 8
7
4 1
2
43
5
56
New
T R..
1 2
3
45
LS
Nut (drive sprocket)
75 Nm (7.5 m·kgf, 54 ft·lbf)
Bolt (drive sprocket cover)
7 Nm (0.7 m·kgf, 5.1 ft·lbf)
New
T R..
T R..
21

CAMSHAFT
5-11
EAS1SL5208
CAMSHAFT
Removing the cylinder head cover
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.
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
For installation, reverse the removal proce-
dure.
31
4
6
5 3
2
3
10 Nm (1.0 mkgf, 7.2 ftIbf)T.R
.
13 Nm (1.3 mkgf, 9.4 ftIbf)T.R
.