2015 YAMAHA YZ250F key

EAS1SM5003
INTRODUCTION
Congratulations on your purchase of a Yamaha YZ series. This model is the culmination of Yamaha’s
vast experience in the production of pacesetting racing machines. It represents the highest grade of
craftsmanship and reliability that have made Yamaha a leader.
This manual explains operation, inspection, basic maintenance and tuning of your machine. If you
have any questions about this manual or your machine, please contact your Yamaha dealer.
TIP
Yamaha continually seeks advancements in product design and quality. Therefore, while this manual
contains the most current product information available at the time of printing, there may be minor
discrepancies between your machine and this manual. If you have any questions concerning this
manual, please consult your Yamaha dealer.
EWA1DX0001
WARNING
PLEASE READ THIS MANUAL CAREFULLY AND COMPLETELY BEFORE OPERATING THIS
MACHINE. DO NOT ATTEMPT TO OPERATE THIS MACHINE UNTIL YOU HAVE ATTAINED A
SATISFACTORY KNOWLEDGE OF ITS CONTROLS AND OPERATING FEATURES AND UNTIL
YOU HAVE BEEN TRAINED IN SAFE AND PROPER RIDING TECHNIQUES. REGULAR INSPEC-
TIONS AND CAREFUL MAINTENANCE, ALONG WITH GOOD RIDING SKILLS, WILL ENSURE
THAT YOU SAFETY ENJOY THE CAPABILITIES AND THE RELIABILITY OF THIS MACHINE.
EAS1SM5004
IMPORTANT MANUAL INFORMATION
Particularly important information is distinguished in this manual by the following notations.
This is the safety alert symbol. It is used to alert you to potential personal
injury hazards. Obey all safety messages that follow this symbol to avoid
possible injury or death.
A WARNING indicates a hazardous situation which, if not avoided, could
result in death or serious injury.
A NOTICE indicates special precautions that must be taken to avoid
damage to the vehicle or other property.
A TIP provides key information to make procedures easier or clearer.
WARNING
NOTICE
TIP

AC MAGNETO................................................................................................ 5-58
REMOVING THE AC MAGNETO............................................................. 5-59
CHECKING THE AC MAGNETO ............................................................. 5-59
CHECKING THE WOODRUFF KEY ........................................................ 5-59
INSTALLING THE AC MAGNETO ........................................................... 5-59
CRANKCASE................................................................................................. 5-61
DISASSEMBLING THE CRANKCASE..................................................... 5-64
REMOVING THE CRANKCASE BEARING ............................................. 5-64
CHECKING THE TIMING CHAIN, TIMING CHAIN GUIDE,
OIL STRAINER ........................................................................................ 5-64
CHECKING THE CRANKCASE ............................................................... 5-64
INSTALLING THE OIL SEAL................................................................... 5-65
ASSEMBLING THE CRANKCASE........................................................... 5-65
CRANKSHAFT ASSEMBLY AND BALANCER SHAFT............................... 5-66
REMOVING THE CRANKSHAFT ASSEMBLY ........................................ 5-67
CHECKING THE CRANKSHAFT ASSEMBLY......................................... 5-67
INSTALLING THE CRANKSHAFT ASSEMBLY....................................... 5-68
INSTALLING THE BALANCER SHAFT ................................................... 5-68
TRANSMISSION............................................................................................. 5-69
REMOVING THE TRANSMISSION ......................................................... 5-70
CHECKING THE SHIFT FORKS.............................................................. 5-70
CHECKING THE SHIFT DRUM ASSEMBLY ........................................... 5-71
CHECKING THE TRANSMISSION .......................................................... 5-71
INSTALLING THE TRANSMISSION ........................................................ 5-71

AC MAGNETO
5-58
EAS1SM5273
AC MAGNETO
Removing the AC magneto
Order Part name Q’ty Remarks
Engine oilDrain.
Refer to “CHANGING THE ENGINE OIL” on
page 3-15.
Seat Refer to “GENERAL CHASSIS” on page 4-1.
Air scoop (left) Refer to “GENERAL CHASSIS” on page 4-1.
1 AC magneto coupler Disconnect.
2 Crankshaft position sensor coupler 1 Disconnect.
3 Shift pedal 1
4 Left crankcase cover 1
5 Gaskets 1
6 Dowel pin 2
7Holder 1
8 Stator assembly 1
9 Rotor 1
10 Woodruff key 1
For installation, reverse the removal proce-
dure.
110
2
4 7 5 8 3
96
8 Nm (0.8 mkgf, 5.8 ftIbf)T.R.
8 Nm (0.8 mkgf, 5.8 ftIbf)T.R.
10 Nm (1.0 mkgf, 7.2 ftIbf)T.R.
10 Nm (1.0 mkgf, 7.2 ftIbf)T.R.
65 Nm (6.5 mkgf, 47 ftIbf)T.R.
New
LT
6
LT
LT
12 Nm (1.2 mkgf, 8.7 ftIbf)T.R.

AC MAGNETO
5-59
EAS1SM5274REMOVING THE AC MAGNETO
1. Remove:
• Nut (rotor) “1”
• Washers
2. Remove:
• Rotor “1”
Use the rotor puller “2” to remove the rotor.
• Woodruff key
EAS1SM5275CHECKING THE AC MAGNETO
1. Check:
• Rotor inner surface “a”
• Stator outer surface “b”
Damage  Inspect the crankshaft runout
and crankshaft bearing.
EAS1SM5276
CHECKING THE WOODRUFF KEY
1. Check:
• Woodruff key “1”
Damage  Replace.
EAS1SM5277INSTALLING THE AC MAGNETO
1. Install:
• Stator “1”
• Screw (stator) “2”
• Crankshaft position sensor “3”
• Bolt (crankshaft position sensor) “4”
• Holder “5”
• Bolt (holder) “6”
TIP
• Apply the sealant to the grommet of the AC
magneto lead.
• Tighten the stator screws using the T25 bit.
• Pass the AC magneto lead “a” through the
crankcase cover side. Rotor puller
90890-04151
YM-04151
1
ab
Screw (stator)
8 Nm (0.8 m·kgf, 5.8ft·lbf)
LOCTITE®
Bolt (crankshaft position sensor)
10 Nm (1.0 m·kgf, 7.2 ft·lbf)
LOCTITE®
Holder
8 Nm (0.8 m·kgf, 5.8 ft·lbf)
LOCTITE®
Three Bond No.1215®
90890-85505
T R..
T R..
26
5
4
3
4a
1
LT
LT

AC MAGNETO
5-60
2. Install:
• Woodruff key “1”
• Rotor “2”
TIP
• Clean the contact surfaces of the tapered por-
tions of the crankshaft and rotor.
• When installing the woodruff key, make sure
that its flat surface “a” is in parallel with the
crankshaft center line “b”.
• When installing the rotor, align the keyway “c”
of the rotor with the woodruff key.
3. Install:
• Washers
• Nut (rotor) “1”
4. Install:
• Dowel pin “1”
• Gasket (left crankcase cover) “2”
• Left crankcase cover “3”
• Lead holder “4”
• Bolt (left crankcase cover) “5”
TIP
Tighten the bolts in stages and in a crisscross
pattern.5. Connect:
• AC magneto lead
Refer to “CABLE ROUTING DIAGRAM” on
page 2-31.
Nut (rotor)
65 Nm (6.5 m·kgf, 47 ft·lbf)
Bolt (left crankcase cover)
10 Nm (1.0 m·kgf, 7.2 ft·lbf)
b11
c
2 a
T R..
1
New
T R..
1
1
2
3
5
5
5
5
4
45

TROUBLESHOOTING
9-1
EAS1SM5351
TROUBLESHOOTING
EAS1SM5352GENERAL INFORMATION
TIP
The following guide for troubleshooting does
not cover all the possible causes of trouble. It
should be helpful, however, as a guide to basic
troubleshooting. Refer to the relative procedure
in this manual for checks, adjustments, and re-
placement of parts.
EAS1SM5353STARTING FAILURES
Engine
1. Cylinder and cylinder head
• Loose spark plug
• Loose cylinder head or cylinder
• Damaged cylinder head gasket
• Damaged cylinder gasket
• Worn or damaged cylinder
• Incorrect valve clearance
• Improperly sealed valve
• Incorrect valve-to-valve-seat contact
• Incorrect valve timing
• Faulty valve spring
• Seized valve
2. Piston and piston ring(s)
• Improperly installed piston ring
• Damaged, worn or fatigued piston ring
• Seized piston ring
• Seized or damaged piston
3. Air filter
• Improperly installed air filter
• Clogged air filter element
4. Crankcase and crankshaft
• Improperly assembled crankcase
• Seized crankshaft
Fuel system
1. Fuel tank
• Empty fuel tank
• Clogged fuel tank breather hose
• Deteriorated or contaminated fuel
• Clogged or damaged fuel hose
2. Fuel pump
• Faulty fuel pump
3. Throttle body
• Deteriorated or contaminated fuel
• Sucked-in airElectrical system
1. Spark plug
• Incorrect spark plug gap
• Incorrect spark plug heat range
• Fouled spark plug
• Worn or damaged electrode
• Worn or damaged insulator
2. Ignition coil
• Cracked or broken ignition coil body
• Broken or shorted primary or secondary
coils
3. Ignition system
• Faulty ECU
• Faulty crankshaft position sensor
• Broken generator rotor woodruff key
4. Switches and wiring
• Faulty ECU
• Faulty engine stop switch
• Broken or shorted wiring
• Faulty neutral switch
• Improperly grounded circuit
• Loose connections
EAS1SM5354INCORRECT ENGINE IDLING SPEED
Engine
1. Cylinder and cylinder head
• Incorrect valve clearance
• Damaged valve train components
2. Air filter
• Clogged air filter element
Fuel system
1. Throttle body
• Damaged or loose throttle body joint
• Improperly synchronized throttle bodies
• Improper throttle cable free play
• Flooded throttle body
Electrical system
1. Spark plug
• Incorrect spark plug gap
• Incorrect spark plug heat range
• Fouled spark plug
• Worn or damaged electrode
• Worn or damaged insulator
• Faulty spark plug cap
2. Ignition coil
• Broken or shorted primary or secondary
coils
• Cracked or broken ignition coil

TROUBLESHOOTING
9-2
3. Ignition system
• Faulty ECU
• Faulty crankshaft position sensor
• Broken generator rotor woodruff key
EAS1SM5355POOR MEDIUM-AND-HIGH-SPEED PER-
FORMANCE
Refer to “STARTING FAILURES” on page 9-1.
Engine
1. Air filter
• Clogged air filter element
Fuel system
1. Fuel pump
• Faulty fuel pump
2. Throttle body
• Defective throttle body
3. ECU
• Faulty ECU
EAS1SM5356FAULTY GEAR SHIFTING
Shifting is difficult
Refer to “CLUTCH” on page 5-35.
EAS1SM5357SHIFT PEDAL DOES NOT MOVE
Shift shaft
• Bent shift shaft
Shift drum and shift forks
• Foreign object in a shift drum groove
• Seized shift fork
• Bent shift fork guide bar
Transmission
• Seized transmission gear
• Foreign object between transmission gears
• Improperly assembled transmission
EAS1SM5358JUMPS OUT OF GEAR
Shift shaft
• Incorrect shift pedal position
• Improperly returned stopper lever
Shift forks
• Worn shift fork
Shift drum
• Incorrect axial play
• Worn shift drum groove
Transmission
• Worn gear dog
EAS1SM5359FAULTY CLUTCH
Clutch slips
1. Clutch
• Improperly assembled clutch
• Loose or fatigued clutch spring
• Worn friction plate
• Worn clutch plate
2. Engine oil
• Incorrect oil level
• Incorrect oil viscosity (low)
• Deteriorated oil
Clutch drags
1. Clutch
• Unevenly tensioned clutch springs
• Warped pressure plate
• Bent clutch plate
• Swollen friction plate
• Bent clutch push rod
• Damaged clutch boss
• Burnt primary driven gear bushing
2. Engine oil
• Incorrect oil level
• Incorrect oil viscosity (high)
• Deteriorated oil
EAS1SM5360OVERHEATING
Engine
1. Cylinder head and piston
• Heavy carbon buildup
• Clogged coolant passages
2. Engine oil
• Incorrect oil level
• Incorrect oil viscosity
• Inferior oil quality
Cooling system
1. Coolant
• Low coolant level
2. Radiator
• Damaged or leaking radiator
• Faulty radiator cap
• Bent or damaged radiator fin
3. Water pump
• Damaged or faulty water pump
• Damaged hose
• Improperly connected hose
• Damaged pipe
• Improperly connected pipe