engine YAMAHA YZ250F 2003 Repair Manual

4 - 47
ENGCYLINDER AND PISTON
2. Position:
Top ring
2nd ring
Oil ring
Offset the piston ring end gaps as
shown.
aTop ring end
b2nd ring end
cOil ring end (upper)
dOil ring
eOil ring end (lower)
3. Install:
Piston 1
Piston pin 2
Piston pin clip 3
NOTE:
Apply engine oil onto the piston pin and pis-
ton.
Be sure that the arrow mark a on the piston
points to the exhaust side of the engine.
Before installing the piston pin clip, cover the
crankcase with a clean rag to prevent the
piston pin clip from falling into the crankcase.
Install the piston pin clips with their ends fac-
ing downward.
45°
135°135°
a
b ced
3New
Cylinder
1. Lubricate:
Piston
Piston ring
Cylinder
NOTE:
Apply a liberal coating of engine oil.
2. Install:
Dowel pin 1
O-ring 2
NOTE:
Apply the lithium soap base grease on the O-
ring.

4 - 49
ENGCLUTCH
EC4A0000
CLUTCH
Extent of removal:1 Push rod 1, 2 and push lever shaft removal2 Push pod 1 disassembly
3 Friction plate and clutch plate removal4 Primary driven gear removal
Extent of removal Order Part name Q’ty Remarks
CLUTCH REMOVAL
Preparation for removal Drain the engine oil. Refer to “ENGINE OIL REPLACEMENT”
section in the CHAPTER 3.
Brake pedal Refer to “ENGINE REMOVAL” section.
Clutch cable Disconnect at engine side.
1 Clutch cover 1
2 Clutch spring 5
3 Pressure plate 1
4 Push rod 1 1
5 Circlip 1
6 Washer 1
7 Bearing 1
8 Ball 1
9Push rod 2
1
4
1
12
3

4 - 53
ENG

CLUTCH
EC4A5000
ASSEMBLY AND INSTALLATION
Push lever shaft
1. Install:

Push lever shaft
1


Bolt (push lever shaft)
2

NOTE:


Apply the lithium soap base grease on the oil
seal lip.

Apply the engine oil on the push lever shaft.

Fit the seat plate
3
in the groove
a
of the
push lever shaft and tighten the bolt (seat
plate).
3
1a2
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)

Clutch
1. Install:

Primary driven gear 1
Thrust washer 2
Clutch boss 3
NOTE:
Apply the engine oil on the primary driven gear
inner circumference.
2. Install:
Lock washer 1
Nut (clutch boss) 2
NOTE:
Use the clutch holding tool 3 to hold the clutch
boss.
ÅFor USA and CDN
ıExcept for USA and CDN
Clutch holding tool:
YM-91042/90890-04086
T R..60 Nm (6.0 m · kg, 43 ft · lb)
Å
ı

4 - 54
ENG
3. Bend the lock washer 1 tab.
4. Install:
Seat plate 1
Cushion spring 2
NOTE:
Install the seat plate with its chamfered por-
tion a facing the clutch boss 3.
Install the seat plate so that it is not caught
on the step b.
Install the cushion spring with the paint c
facing out.
1
2
c
3
a
b
5. Install:
Friction plate 1 1
Clutch plate 1 2
Friction plate 2 3
Clutch plate 2 4
NOTE:
Install the clutch plates and friction plates
alternately on the clutch boss, starting with a
friction plate and ending with a friction plate.
Use the friction plates 1 for the first and final
while paying attention to the difference in
surface pattern.
Apply the engine oil on the friction plates and
clutch plates.
Unlike the clutch plate 2, the clutch plate 1
has no surface gloss. Use the clutch plate 1
for the first while paying attention to the dif-
ference in surface gloss.
6. Install:
Bearing 1
Washer 2
Circlip 3
To push rod 1 4.
NOTE:
Apply the engine oil on the bearing and
washer.
CLUTCH

4 - 55
ENGCLUTCH
7. Install:
Push rod 2 1
Ball 2
Push rod 1 3
NOTE:
Apply the engine oil on the push rod 1, 2 and
ball.
8. Install:
Pressure plate 1
9. Install:
Clutch spring 1
Bolt (clutch spring) 2
NOTE:
Tighten the bolts in stage, using a crisscross
pattern.
T R..8 Nm (0.8 m · kg, 5.8 ft · lb)
10. Install:
Dowel pin 1
Gasket (clutch cover) 2
11. Install:
Clutch cover 1
Bolt (clutch cover)
NOTE:
Tighten the bolts in stage, using a crisscross
pattern.
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)

4 - 56
ENG
OIL FILTER ELEMENT, WATER PUMP AND RIGHT
CRANKCASE COVER
OIL FILTER ELEMENT, WATER PUMP AND RIGHT
CRANKCASE COVER
Extent of removal:1 Oil filter element removal2 Water pump removal
3 Right crankcase cover removal
Extent of removal Order Part name Q’ty Remarks
OIL FILTER ELEMENT, WATER
PUMP AND RIGHT CRANK-
CASE COVER REMOVAL
Preparation for removal Drain the engine oil. Refer to “ENGINE OIL REPLACEMENT”
section in the CHAPTER 3.
Drain the coolant. Refer to “COOLANT REPLACEMENT”
section in the CHAPTER 3.
Radiator hose 3 Disconnect at water pump side.
Exhaust pipe Refer to “EXHAUST PIPE AND
SILENCER” section.
Brake pedal Refer to “ENGINE REMOVAL” section.
Right engine guard
1 Oil filter element cover 1
2 Oil filter element 1
13

4 - 61
ENG
OIL FILTER ELEMENT, WATER PUMP AND RIGHT
CRANKCASE COVER
2. Install:
Right crankcase cover 1
Bolt (right crankcase cover) 2
NOTE:
Apply the engine oil on the impeller shaft
end.
Mesh the impeller shaft gear 3 with primary
drive gear 4.
Tighten the bolts in stage, using a crisscross
pattern.
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
Kickstarter crank
1. Install:
Kickstarter crank 1
Washer 2
Bolt (kickstarter crank) 3
NOTE:
Install the kickstarter crank so that the kick-
starter crank is as vertical as possible with the
distance a between the kickstarter crank and
the frame being 8 mm (0.31 in) or more.
2. Install:
Oil hose 1
Bolt (oil hose) 2
T R..33 Nm (3.3 m · kg, 24 ft · lb)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
3. Install:
Copper washer 1
Oil delivery pipe 2
Union bolt (M8) 3
Union bolt (M10) 4
T R..18 Nm (1.8 m · kg, 13 ft · lb)
T R..20 Nm (2.0 m · kg, 14 ft · lb)

4 - 65
ENGBALANCER
ASSEMBLY AND INSTALLATION
Balancer shaft, balancer shaft drive gear
and balancer shaft driven gear
1. Install:
Balancer shaft 1
NOTE:
Apply the engine oil on the bearing.
When installing the balancer shaft, align the
center a of the balancer shaft weight along
the line connecting the centers of the crank-
shaft and balancer shaft.
2. Install:
Balancer shaft driven gear 1
NOTE:
Install the balancer shaft driven gear onto the
balancer shaft while aligning the punch mark
a on the balancer shaft driven gear with the
lower spline b on the balancer shaft end.
3. Install:
Balancer shaft drive gear 1
NOTE:
Align the punched mark a on the balancer
shaft drive gear with the punched mark b on
the balancer shaft driven gear 2.
Align the punched mark c on the balancer
shaft drive gear with the lower spline d on
the crankshaft end.
4. Install:
Lock washer 1
Nut (balancer shaft driven gear) 2
Primary drive gear 3
Nut (primary drive gear) 4
NOTE:
Install the primary drive gear with its stepped
side a facing the engine.
Place an aluminum plate b between the
teeth of the balancer shaft drive gear 5 and
driven gear 6.
5. Bend the lock washer tab.
T R..50 Nm (5.0 m · kg, 36 ft · lb)
T R..75 Nm (7.5 m · kg, 54 ft · lb)

4 - 69
ENGOIL PUMP
ASSEMBLY AND INSTALLATION
Oil pump
1. Install:
Oil pump drive shaft 1
Washer 2
Dowel pin 3
Inner rotor 1 4
NOTE:
Apply the engine oil on the oil pump drive
shaft and inner rotor 1.
Fit the dowel pin into the groove in the inner
rotor 1.
2. Install:
Outer rotor 1 1
NOTE:
Apply the engine oil on the outer rotor 1.
3. Install:
Oil pump cover 1
Screw (oil pump cover) 2
Dowel pin 3
Inner rotor 2 4
Circlip 5
NOTE:
Apply the engine oil on the inner rotor 2.
Fit the dowel pin into the groove in the inner
rotor 2.
T R..2 Nm (0.2 m · kg, 1.4 ft · lb)

4 - 70
ENG
4. Install:
Outer rotor 2 1
Dowel pin 2
Oil pump assembly 3
Bolt (oil pump assembly)
[L = 25 mm (0.94 in)] 4
Bolt (oil pump assembly)
[L = 30 mm (1.18 in)] 5
NOTE:
Apply the engine oil on the outer rotor 2.
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
5. Install:
Oil pump drive gear 1
Washer 2
Circlip 3
NOTE:
Apply the engine oil on the oil pump drive gear
inner circumference.
OIL PUMP