engine YAMAHA YZ250F 2003 Manual PDF

4 - 75
ENGKICK SHAFT AND SHIFT SHAFT
EC4B5111
Stopper lever
1. Install:
Torsion spring 1
Stopper lever 2
Bolt (stopper lever) 3
NOTE:
Align the stopper lever roller with the slot on
segment.
Shift guide and shift lever assembly
1. Install:
Spring 1
Pawl pin 2
Pawl 3
To shift lever 4.
NOTE:
Apply the engine oil on the spring, pawl pin
and pawl.
2. Install:
Shift lever assembly 1
To shift guide 2.
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
3. Install:
Shift lever assembly 1
Shift guide 2
NOTE:
The shift lever assembly is installed at the
same time as the shift guide.
Apply the engine oil on the bolt (segment)
shaft.
4. Install:
Bolt (shift guide) 1
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)

4 - 76
ENGKICK SHAFT AND SHIFT SHAFT
Shift shaft
1. Install:
Roller 1
Collar 2
Torsion spring 3
Shift shaft 4
NOTE:
Apply the engine oil on the roller and shift
shaft.
2. Install:
Shift pedal 1
Bolt (shift pedal) 2
NOTE:
When installing the shift pedal onto the shift
shaft, be sure that the center of the shift pedal
is about 1 mm (0.04 in) a above the top of the
footrest.
T R..12 Nm (1.2 m · kg, 8.7 ft · lb)
Kick shaft assembly
1. Install:
Kick gear 1
Washer 2
Circlip 3
Ratchet wheel 4
Spring 5
Washer 6
Circlip 7
To kick shaft 8.
NOTE:
Apply the molybdenum disulfide oil on 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 kick shaft 2.
NOTE:
Make sure the stopper a of the torsion spring
fits into the hole b on the kick shaft.

4 - 77
ENGKICK SHAFT AND SHIFT SHAFT
3. Install:
Spring guide 1
NOTE:
Slide the spring guide into the kick shaft, make
sure the groove a in the spring guide fits on
the stopper of the torsion spring.
4. Install:
Kick shaft assembly 1
Washer 2
NOTE:
Apply the molybdenum disulfide grease on
the contacting surfaces of the kick shaft stop-
per a and stopper plate 3.
Apply the engine oil on the kick shaft.
Slide the kick shaft assembly into the crank-
case and make sure the kick shaft stopper a
fits into the stopper plate.
5. Hook:
Torsion spring 1
NOTE:
Turn the torsion spring clockwise and hook
into the proper hole a in the crankcase.
Kick idle gear
1. Install:
Kick idle gear 1
Washer 2
Circlip 3
NOTE:
Apply the engine oil on the kick idle gear
inner circumference.
Install the kick idle gear with its depressed
side a toward you.

4 - 82
ENGENGINE REMOVAL
EC4M0000
ENGINE REMOVAL
Extent of removal Order Part name Q’ty Remarks
ENGINE REMOVAL
Preparation for removal Hold the machine by placing the
suitable stand under the frame.
WARNING
Support the machine securely so there is no
danger of it falling over.
Seat and fuel tank Refer to “SEAT, FUEL TANK AND SIDE
COVERS” section.
Carburetor Refer to “CARBURETOR” section.
Exhaust pipe and silencer Refer to “EXHAUST PIPE AND
SILENCER” section.
Clutch cable Disconnect at engine side.
Radiator Refer to “RADIATOR” section.
Shift pedal Refer to “KICK SHAFT AND SHIFT
SHAFT” section.
Cylinder head breather hose and
oil tank breather hoseRefer to “CAMSHAFTS” section.
Drain the engine oil Refer to “ENGINE OIL REPLACEMENT”
section in the CHAPTER 3.

4 - 83
ENGENGINE REMOVAL
Extent of removal:1 Engine removal
Extent of removal Order Part name Q’ty Remarks
Ignition coil
Disconnect the CDI magneto lead.
Right engine guard
1 Lower engine guard 1
2 Neutral switch 1
3 Bolt (oil hose) 2
4 Drive chain sprocket cover 1
5 Nut (drive sprocket) 1
Refer to “REMOVAL POINTS”. 6 Lock washer 1
7 Drive sprocket 1
8 Clip 1
9 Bolt (brake pedal) 1
10 Brake pedal 1
11 Upper engine bracket 2
12 Lower engine bracket 2
13 Engine mounting bolt 3
14 Pivot shaft 1
Refer to “REMOVAL POINTS”.
15 Engine 1
1

4 - 84
ENGENGINE REMOVAL
EC4M3000
REMOVAL POINTS
EC4F3100
Drive sprocket
1. Remove:
Nut (drive sprocket) 1
Lock washer 2
NOTE:
Straighten the lock washer tab.
Loosen the nut while applying the rear brake.
2. Remove:
Drive sprocket 1
Drive chain 2
NOTE:
Remove the drive sprocket together with the
drive chain.
EC4M3301
Engine removal
1. Remove:
Pivot shaft 1
NOTE:
If the pivot shaft is pulled all the way out, the
swingarm will come loose. If possible, insert a
shaft of similar diameter into the other side of
the swingarm to support it.
2. Remove:
Engine 1
From right side.
NOTE:
Make sure that the couplers, hoses and cables
are disconnected.
1

4 - 85
ENGENGINE REMOVAL
EC4M5000
ASSEMBLY AND INSTALLATION
Engine installation
1. Install:
Engine 1
Install the engine from right side.
Pivot shaft 2
Engine mounting bolt (lower) 3
Lower engine bracket 4
Bolt (engine bracket) 5
Engine mounting bolt (front) 6
Upper engine bracket 7
Engine mounting bolt (upper) 8
Lower engine guard 9
Bolt (lower engine guard) 0
NOTE:
Apply the molybdenum disulfide grease on the
pivot shaft.
EC4M5211
Brake pedal
1. Install:
Spring 1
Brake pedal 2
O-ring 3
Bolt (brake pedal) 4
Clip 5
NOTE:
Apply the lithium soap base grease on the
bolt, O-rings and brake pedal bracket.
Install the clip with its stopper portion a fac-
ing inward.
T R..85 Nm (8.5 m · kg, 61 ft · lb)
T R..69 Nm (6.9 m · kg, 50 ft · lb)
T R..34 Nm (3.4 m · kg, 24 ft · lb)
T R..69 Nm (6.9 m · kg, 50 ft · lb)
T R..55 Nm (5.5 m · kg, 40 ft · lb)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
T R..26 Nm (2.6 m · kg, 19 ft · lb)
Drive sprocket
1. Install:
Drive sprocket 1
Drive chain 2
NOTE:
Install the drive sprocket together with the
drive chain.

4 - 86
ENGENGINE REMOVAL
2. Install:
Lock washer 1
Nut (drive sprocket) 2
NOTE:
Tighten the nut while applying the rear brake.
T R..75 Nm (7.5 m · kg, 54 ft · lb)
3. Bend the lock washer tab to lock the nut.
4. Install:
Drive chain sprocket guide 1
Drive chain sprocket cover 2
Screw (drive chain sprocket cover) 3
T R..8 Nm (0.8 m · kg, 5.8 ft · lb)
Oil hose and neutral switch
1. Install:
O-ring 1
Dowel pin 2
Oil hose 3
Bolt (oil hose) 4
NOTE:
Apply the lithium soap base grease on the O-
ring.
2. Install:
Spring 1
Pin 2
O-ring 3
Neutral switch 4
Screw (neutral switch) 5
NOTE:
Apply the lithium soap base grease on the O-
ring.
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
T R..4 Nm (0.4 m · kg, 2.9 ft · lb)

4 - 87
ENGCRANKCASE AND CRANKSHAFT
CRANKCASE AND CRANKSHAFT
Extent of removal:1 Crankcase separation2 Crankshaft removal
Extent of removal Order Part name Q’ty Remarks
CRANKCASE AND CRANK-
SHAFT REMOVAL
Preparation for removal Engine Refer to “ENGINE REMOVAL” section.
Piston Refer to “CYLINDER AND PISTON” sec-
tion.
Kick shaft assembly
Refer to “KICK SHAFT AND SHIFT
SHAFT” section.
Segment
Stator Refer to “CDI MAGNETO” section.
Balancer shaft Refer to “BALANCER” section.
1 Timing chain guide (intake side) 1
2 Timing chain 1
3Oil delivery pipe 2
1
21

4 - 90
ENGCRANKCASE AND CRANKSHAFT
REMOVAL POINTS
Crankcase
1. Separate:
Right crankcase
Left crankcase
Separation steps:
Remove the crankcase bolts 1, hose
guide 2 and clutch cable holder 3.
NOTE:
Loosen each bolt 1/4 of a turn at a time and
after all the bolts are loosened, remove
them.
Remove the right crankcase 4.
NOTE:
Place the crankcase with its left side
downward and split it by inserting a screw-
driver tip into the splitting slit a in the
crankcase.
Lift the right crankcase horizontally while
lightly patting the case splitting slit and
engine mounting boss using a soft ham-
mer, and leave the crankshaft and trans-
mission with the left crankcase.
CAUTION:
Use soft hammer to tap on the case half.
Tap only on reinforced portions of case.
Do not tap on gasket mating surface.
Work slowly and carefully. Make sure the
case halves separate evenly. If one end
“hangs up”, take pressure off the push
screw, realign, and start over. If the
cases do not separate, check for a
remaining case screw or fitting. Do not
force.
Remove the dowel pins and O-ring.
a
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