2014 YAMAHA YZ250F checking oil

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 ........................................................................................ 5-66
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

CAMSHAFT
5-16
EAS1SM1212CHECKING THE DECOMPRESSION SYS-
TEM
1. Check:
• Decompression system
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a. Check that the decompressor cam “1”
moves smoothly.
b. Check that the decompressor lever pin “2”
projects from the camshaft.
▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲EAS1SM1213INSTALLING THE CAMSHAFTS
1. Install:
• Exhaust camshaft “1”
• Intake camshaft “2”
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a. Turn the crankshaft counterclockwise with a
wrench.
TIP
• Apply molybdenum disulfide oil to the cam-
shafts.
• Apply the engine oil on the decompression
system.
b. Align the top dead center (TDC) mark “a” on
the rotor with the alignment mark “b” on the
crankcase cover.c. Fit the timing chain “3” onto both camshaft
sprockets and install the camshafts on the
cylinder head.
TIP
Make sure that the alignment mark “c” on the
exhaust camshaft sprocket and the alignment
mark “d” on the intake camshaft sprocket are
aligned with the edge of the cylinder head.
ECA33DD029
NOTICE
Do not turn the crankshaft during the cam-
shaft installation. Damage or improper
valve timing will result.
d. Install the clips, the camshaft caps and the
bolts (camshaft cap).
TIP
• Before installing the clips, cover the cylinder
head with a clean cloth to prevent the clips
from coming off into the cylinder head cavity.
• Tighten the bolts to the specified torque in two
or three steps in the proper tightening se-
quence as shown.
ECA33DD030
NOTICE
The bolts (camshaft cap) must be tightened
evenly, or damage to the cylinder head,
camshaft caps, and camshaft will result.
1
2
Bolt (camshaft cap)
10 Nm (1.0 m·kgf, 7.2 ft·lbf)
b
a
dc
3
T R..

VALVES AND VALVE SPRINGS
5-25
TIP
After replacing the valve guide, reface the valve
seat.
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3. Eliminate:• Carbon deposits(from the valve face and valve seat)
4. Check: • Valve facePitting/wear  Grind the valve face.
• Valve stem end Mushroom shape or diameter larger than
the body of the valve stem  Replace the
valve.
5. Measure: • Valve margin thickness D “a”Out of specification  Replace the valve. 6. Measure:
• Valve stem runoutOut of specification  Replace the valve.
TIP
• When installing a new valve, always replace
the valve guide.
• If the valve is removed or replaced, always re-
place the oil seal.
EAS1SM1222CHECKING THE VALVE SEATS
1. Eliminate: • Carbon deposits(from the valve face and valve seat)
2. Check:
• Valve seatPitting/wear  Replace the cylinder head.
3. Measure:
• Valve seat width C “a”Out of specification  Replace the cylinder
head.
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a. Apply Mechanic’s blueing dye (Dykem) “b” onto the valve face.
Intake
Valve guide remover (ø5.0)
90890-04097
YM-04097
Valve guide installer (ø5.0) 90890-04098
YM-04098
Valve guide reamer (ø5.0) 90890-04099
YM-04099
Exhaust
Valve guide remover (ø4.5)
90890-04116
YM-04116
Valve guide installer (ø4.5)
90890-04117
YM-04117
Valve guide reamer (ø4.5)
90890-04118
YM-04118
Valve margin thickness D (intake) 1.20 mm (0.0472 in)
Valve margin thickness D (ex-
haust) 0.85 mm (0.0335 in)
Valve stem runout 0.010 mm (0.0004 in)
Valve seat width C (intake) 0.90–1.10 mm (0.0354–0.0433 in)
Valve seat width C (exhaust) 0.90–1.10 mm (0.0354–0.0433 in)

CYLINDER AND PISTON
5-31
EAS1SM1227REMOVING THE PISTON
1. Remove:
• Piston pin clip “1”
• Piston pin “2”
• Piston “3”
ECA13810
NOTICE
Do not use a hammer to drive the piston pin
out.
TIP
• Before removing the piston pin clip, cover the
crankcase opening with a cloth to prevent the
piston pin clip from falling into the crankcase.
• Before removing the piston pin, deburr the
piston pin clip’s groove and the piston pin’s
bore area. If the piston pin groove is deburred
and the piston pin is still difficult to remove,
use the piston pin puller set “4”.
2. Remove:
• Top ring
• Oil ring
TIP
When removing a piston ring, open the end gap
with your fingers and lift the opposite end gap
of the piston ring over the piston crown.
EAS1SM1228CHECKING THE CYLINDER AND PISTON
1. Check:
• Piston wall (Sidewall)
• Cylinder wall
Vertical scratches  Replace the cylinder,
and replace the piston and piston rings as a
set.
2. Measure:
• Piston-to-cylinder clearance
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a. Measure the cylinder bore with the cylinder
bore gauge.
TIP
Measure cylinder bore by taking side-to-side
and front-to-back measurements of the cylin-
der. Then, find the average of the measure-
ments. Piston pin puller set
90890-01304
Piston pin puller
YU-01304
1
Bore
77.000–77.010 mm (3.0315–
3.0319 in)
Taper limit
0.050 mm (0.0020 in)
Out of round limit
0.050 mm (0.0020 in)
Cylinder bore = maximum of D
1–D6
Taper limit = (maximum of D1or D2) - (maxi-
mum of D
5 or D6)
Out of round limit = maximum of D
1, D3 or D5
- minimum of D
2, D4 or D6

CYLINDER AND PISTON
5-32
b. If out of specification, rebore or replace the
cylinder, and replace the piston and the pis-
ton rings as a set.
c. Measure the piston outside diameter D “a” at
the measurement position H “b” with the mi-
crometer.
d. If out of specification, replace the cylinder,
the piston, and the piston rings as a set.
e. Calculate the piston-to-cylinder clearance
with the following formula.
f. If out of specification, replace the cylinder,
the piston, and the piston rings as a set.
▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲▲EAS1SM1229CHECKING THE PISTON RINGS
1. Measure:
• Piston ring side clearance
Out of specification  Replace the piston
and piston rings as a set.
TIP
Before measuring the piston ring side clear-
ance, eliminate any carbon deposits from the
piston ring grooves and piston rings.2. Install:
• Piston rings
TIP
Level the piston ring into the cylinder with the
piston.
3. Measure:
• Piston ring end gap
Out of specification  Replace the piston
ring.
TIP
The oil ring expander’s end gap cannot be
measured. If the oil ring rail’s gap is excessive,
replace all three oil rings.
EAS1SM1230
Diameter D
76.955–76.970 mm (3.0297–
3.0303 in)
Measurement position H
9.0 mm (0.35 in)
Piston-to-cylinder clearance =
Cylinder bore - Piston diameter
Piston-to-cylinder clearance
0.030–0.055 mm (0.0012–0.0022
in)
Limit
0.15 mm (0.006 in)
ba
Ring side clearance
0.030–0.065 mm (0.0012–0.0026
in)
Limit
0.120 mm (0.0047 in)
a. 10 mm (0.39 in)
Piston ring end gap
Top ring
End gap (installed)
0.15–0.25 mm (0.0059–0.0098 in)
Limit
0.50 mm (0.0197 in)
Oil ring
End gap (installed)
0.10–0.35 mm (0.0039–0.0138 in)

CYLINDER AND PISTON
5-33
CHECKING THE PISTON PIN
1. Check:
• Piston pin
Blue discoloration/grooves  Replace the
piston pin and then check the lubrication
system.
2. Measure:
• Piston pin outside diameter “a”
Out of specification  Replace the piston
pin.
3. Measure:
• Piston pin bore inside diameter “b”
Out of specification  Replace the piston.
EAS1SM1231
INSTALLING THE PISTON AND CYLINDER
1. Install:
• Oil ring expander “1”
• Lower oil ring rail “2”
• Upper oil ring rail “3”
• Top ring “4”
TIP
Be sure to install the piston ring so that the
manufacturer’s marks or numbers face up.
2. Install:
• Piston “1”
• Piston pin “2”
• Piston pin clip “3”
TIP
• Apply the engine oil to the piston pin.
• Install the piston with the F mark “a” on it
pointing to its intake (front) side.
• Before installing the piston pin clip, cover the
crankcase opening with a cloth to prevent the
clip from falling into the crankcase.
• Install the piston pin clips, so that the clip ends
are 3 mm (0.12 in) “c” or more from the cutout
in the piston. Piston pin outside diameter
15.991–16.000 mm (0.6296–
0.6299 in)
Limit
15.971 mm (0.6288 in)
Piston pin bore inside diameter
16.002–16.013 mm (0.6300–
0.6304 in)
Limit
16.043 mm (0.6316 in)b
4
New

CLUTCH
5-40
CHECKING THE PRIMARY DRIVEN GEAR
1. Check:
• Primary driven gear
Damage/wear  Replace the primary drive
and primary driven gears as a set.
Excessive noise during operation  Re-
place the primary drive and primary driven
gears as a set.
EAS1SM1244INSTALLING THE OIL SEAL
1. Install:
• Oil seal “1”
• Washer “2”
• Circlip “3”
TIP
• Apply is lithium-soap-based grease on the oil
seal lip.
• Install the oil seal in parallel with its manufac-
ture's marks or numbers facing inward.
EAS1SM1245INSTALLING THE RIGHT CRANKCASE
COVER
1. Install:
• Dowel pin “1”
• O-rings “2”
• Collar “3”
• Gasket “4”
TIP
Apply the lithium-soap-based grease on the O-
ring.2. Install:
• Right crankcase cover “1”
• Right crankcase cover bolt “2”
TIP
• Apply the engine oil on the impeller shaft end.
• Mesh the impeller shaft gear “3” with primary
drive gear “4”.
• Tighten the right crankcase cover bolts in
stages and in a crisscross pattern.
EAS1SM1246
New
New
3
2
1
LS
New
New
1
1 4
2
New
New
3
LS
Right crankcase cover bolt
10 Nm (1.0 m·kgf, 7.2 ft·lbf)
T R..
3
1
4
E
12

KICKSTATER
5-45
EAS1SM1249REMOVING THE KICK SHAFT ASSEMBLY
1. Remove:
• Kick shaft assembly “1”
TIP
Unhook the torsion spring “2” from the hole “a”
in the crankcase.
EAS1SM1250CHECKING THE KICK SHAFT AND RATCH-
ET WHEEL
1. Check:
• Ratchet wheel “1” smooth movement
Unsmooth movement  Replace.
• Kick shaft “2”
Wear/damage  Replace the kick shaft as-
sembly.
• Spring “3”
Broken  Replace.
EAS1SM1251CHECKING THE KICK GEAR, KICK IDLE
GEAR, AND RATCHET WHEEL
1. Check:
• Kick gear “1”
Wear/damage  Replace the kick shaft as-
sembly.
• Kick idle gear “2”
• Ratchet wheel “3”
• Gear teeth “a”
• Ratchet teeth “b”
Wear/damage  Replace.
EAS1SM1252INSTALLING THE KICK SHAFT ASSEMBLY
1. Install:
• Kick gear “1”
• Washer “2”
• Circlip “3”
• Ratchet wheel “4”
• Spring “5”
• Washer “6”
• Circlip “7”
(to the kick shaft “8”)
TIP
• Apply molybdenum disulfide oil to the inner
circumferences of the kick gear and ratchet
wheel.
• Align the punch mark “a” on the ratchet wheel
with the punch mark “b” on the kick shaft.
2. Install:
• Torsion spring “1”
(to the kick shaft “2”)
TIP
Make sure the stopper “a” of the torsion spring
fits into the hole “b” on the kick shaft.
31
2
a
b
3
12
New
New