engine YAMAHA YZ250F 2001 Repair Manual

4 - 40
ENGVALVES AND VALVE SPRINGS
3. Install:
lValve cotter
NOTE:
While compressing the valve spring with a
valve spring compressor 1 install the valve
cotters.
4. To secure the valve cotters onto the
valve stem, lightly tap the valve tip with a
piece of wood.
CAUTION:
Hitting the valve tip with excessive force
could damage the valve.
Valve spring compressor:
YM-04019/90890-04019
5. Install:
lAdjusting pad 1
lValve lifter 2
NOTE:
lApply the molybdenum disulfied oil on the
valve stem end.
lApply the engine oil on the valve lifters.
lValve lifter must turn smoothly when rotated
with a finger.
lBe careful to reinstall valve lifters and pads
in their original place.

4 - 45
ENGCYLINDER AND PISTON
Piston pin
1. Inspect:
lPiston pin
Blue discoloration/grooves ® Replace,
then inspect the lubrication system.
2. Measure:
lPiston pin-to-piston clearance
ASSEMBLY AND INSTALLATION
Piston ring and piston
1. Install:
lPiston ring
Onto the piston.
NOTE:
lBe sure to install the piston rings so that the
manufacturer’s marks or numbers are
located on the upper side of the rings.
lLubricate the piston and piston rings liberally
with engine oil. Measurement steps:
lMeasure the outside diameter (piston pin)
a.
If out of specification, replace the piston
pin.
Outside diameter (piston pin):
15.991 ~ 16.000 mm
(0.6296 ~ 0.6299 in)
lMeasure the inside diameter (piston) b.
Inside diameter (piston):
16.002 ~ 16.013 mm
(0.6300 ~ 0.6304 in)
lCalculate the piston pin-to-piston clear-
ance with the following formula.
Piston pin-to-piston clearance =
Inside diameter (piston) b –
Outside diameter (piston pin) a
lIf out of specification, replace the piston.
Piston pin-to-piston clearance:
0.002 ~ 0.022 mm
(0.0001 ~ 0.0009 in)
: 0.07 mm (0.003 in)

4 - 46
ENGCYLINDER AND PISTON
2. Position:
lTop ring
l2nd ring
lOil 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:
lPiston 1
lPiston pin 2
lPiston pin clip 3
NOTE:
lApply engine oil onto the piston pin and pis-
ton.
lBe sure that the arrow mark a on the piston
points to the exhaust side of the engine.
lBefore installing the piston pin clip, cover the
crankcase with a clean rag to prevent the
piston pin clip from falling into the crankcase.
lInstall the piston pin clips with their ends fac-
ing downward.
45¡
135¡135¡
a
b ced
3New
Cylinder
1. Lubricate:
lPiston
lPiston ring
lCylinder
NOTE:
Apply a liberal coating of engine oil.
2. Install:
lDowel pin 1
lO-ring 2
NOTE:
Apply the lithium soap base grease on the O-
ring.

4 - 48
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 - 52
ENGCLUTCH
EC4A5000
ASSEMBLY AND INSTALLATION
Push lever shaft
1. Install:
lPush lever shaft 1
lBolt (push lever shaft) 2
NOTE:
lApply the lithium soap base grease on the oil
seal lip.
lApply the engine oil on the push lever shaft.
lFit the seat plate 3 in the groove a of the
push lever shaft and tighten the bolt (seat
plate).
3
1
a2
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
Clutch
1. Install:
lPrimary driven gear 1
lThrust washer 2
lClutch boss 3
NOTE:
Apply the engine oil on the primary driven gear
inner circumference.
2. Install:
lLock washer 1
lNut (clutch boss) 2
NOTE:
Use the clutch holding tool 3 to hold the clutch
boss.
For USA and CDN
õExcept for USA and CDN
Clutch holding tool:
YM-91042/90890-04086
T R..60 Nm (6.0 m · kg, 43 ft · lb)

õ

4 - 53
ENGCLUTCH
3. Bend the lock washer 1 tab.
4. Install:
lSeat plate 1
lCushion spring 2
NOTE:
lInstall the seat plate with its chamfered por-
tion a facing the clutch boss 3.
lInstall the cushion spring with the paint b
facing out.
1
2 1
2 3
a
b
5. Install:
lFriction plate 1 1
lClutch plate 1 2
lFriction plate 2 3
lClutch plate 2 4
NOTE:
lInstall the clutch plates and friction plates
alternately on the clutch boss, starting with a
friction plate and ending with a friction plate.
lUse the friction plates 1 for the first and final
while paying attention to the difference in
surface pattern.
lApply the engine oil on the friction plates and
clutch plates.
lUnlike the clutch plate 2, the clutch plate 1
has no surface gloss. Use the clutch plate 1
for the first while paying attenion to the differ-
ence in surface gloss.
1
2
6. Install:
lBearing 1
lWasher 2
lCirclip 3
To push rod 1 4.
NOTE:
Apply the engine oil on the bearing and
washer.

4 - 54
ENGCLUTCH
7. Install:
lPush rod 2 1
lBall 2
lPush rod 1 3
NOTE:
Apply the engine oil on the push rod 1, 2 and
ball.
8. Install:
lPressure plate 1
9. Install:
lClutch spring 1
lBolt (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:
lDowel pin 1
lGasket (clutch cover) 2
11. Install:
lClutch cover 1
lBolt (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 - 55
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 - 60
ENG
OIL FILTER ELEMENT, WATER PUMP AND RIGHT
CRANKCASE COVER
2. Install:
lRight crankcase cover 1
lBolt (right crankcase cover) 2
NOTE:
lApply the engine oil on the impeller shaft
end.
lMesh the impeller shaft gear 3 with primary
drive gear 4.
lTighten the bolts in stage, using a crisscross
pattern.
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)
Kickstarter crank
1. Install:
lKickstarter crank 1
lWasher 2
lBolt (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:
lOil hose 1
lBolt (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:
lCopper washer 1
lOil delivery pipe 2
lUnion bolt (M8) 3
lUnion 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 - 64
ENGBALANCER
ASSEMBLY AND INSTALLATION
Balancer shaft, balancer shaft drive gear
and balancer shaft driven gear
1. Install:
lBalancer shaft 1
NOTE:
lApply the engine oil on the bearing.
lWhen 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:
lBalancer 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:
lBalancer shaft drive gear 1
NOTE:
lAlign the punched mark a on the balancer
shaft drive gear with the punched mark b on
the balancer shaft driven gear 2.
lAlign the punched mark c on the balancer
shaft drive gear with the lower spline d on
the crankshaft end.
4. Install:
lLock washer 1
lNut (balancer shaft driven gear) 2
lPrimary drive gear 3
lNut (primary drive gear) 4
NOTE:
lInstall the primary drive gear with its stepped
side a facing the engine.
lPlace 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, 3.6 ft · lb)
T R..75 Nm (7.5 m · kg, 54 ft · lb)