Oil YAMAHA YZ250F 2002 Workshop Manual

4 - 38
ENGVALVES AND VALVE SPRINGS
9. Lap:
Valve face
Valve seat
NOTE:
After refacing the valve seat or replacing the
valve and valve guide, the valve seat and
valve face should be lapped.
Lapping steps:
Apply a coarse lapping compound to the
valve face.
CAUTION:
Do not let the compound enter the gap
between the valve stem and the guide.
Apply molybdenum disulfide oil to the
valve stem.
Install the valve into the cylinder head.
Turn the valve until the valve face and
valve seat are evenly polished, then clean
off all of the compound.
NOTE:
For best lapping results, lightly tap the valve
seat while rotating the valve back and forth
between your hands.
Apply a fine lapping compound to the
valve face and repeat the above steps.
NOTE:
After every lapping operation be sure to
clean off all of the compound from the valve
face and valve seat.
Apply Mechanic’s blueing dye (Dykem) to
the valve face.
Install the valve into the cylinder head.
Press the valve through the valve guide
and onto the valve seat to make a clear
pattern.
Measure the valve seat width again. If the
valve seat width is out of specification,
reface and relap the valve seat.

4 - 40
ENG

VALVES AND VALVE SPRINGS
Combination of cylinder head and valve lifter
1. Combination:
For this combination, match the paint color
on the cylinder head with that on the valve
lifter according to the chart below.
NOTE:

When you purchase a cylinder head, you can-
not designate its size. Choose the valve lifter
that matches the above chart.
Combination
Cylinder head mark
a
(color)Valve lifter mark
b

(color)
Red Red
Blue Blue
Yellow Yellow
Purple Black
ASSEMBLY AND INSTALLATION
Valve and valve spring
1. Apply:

Molybdenum disulfide oil
Onto the valve stem and valve stem
seal.
2. Install:

Valve
1


Valve spring seat
2


Valve stem seal
3

Valve spring
4


Valve spring retainer
5

To cylinder head.
NOTE:


Make sure that each valve is installed in its
original place, also referring to the painted
color as follows.
Intake (middle)
a
: yellow
Intake (right/left)
b
: white
Exhaust: no paint

Install the valve springs with the larger pitch
c
facing upward.
d
Smaller pitch

4 - 41
ENGVALVES AND VALVE SPRINGS
3. Install:
Valve 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-4019/90890-04019
5. Install:
Adjusting pad 1
Valve lifter 2
NOTE:
Apply the molybdenum disulfied oil on the
valve stem end.
Apply the engine oil on the valve lifters.
Valve lifter must turn smoothly when rotated
with a finger.
Be careful to reinstall valve lifters and pads
in their original place.

4 - 45
ENGCYLINDER AND PISTON
Piston ring
1. Measure:
Ring side clearance
Use a feeler gauge 1.
Out of specification → Replace the pis-
ton and rings as a set.
NOTE:
Clean carbon from the piston ring grooves and
rings before measuring the side clearance.
2. Position:
Piston ring
(in cylinder)
NOTE:
Insert a ring into the cylinder and push it
approximately 10 mm (0.39 in) into the cylin-
der. Push the ring with the piston crown so that
the ring will be at a right angle to the cylinder
bore.
a10 mm (0.39 in)
Side clearance:
Standard
Top ring0.030 ~ 0.065 mm
(0.0012 ~ 0.0026 in)0.12 mm
(0.005 in)
2nd ring0.020 ~ 0.055 mm
(0.0008 ~ 0.0022 in)0.12 mm
(0.005 in)
3. Measure:
Ring end gap
Out of specification → Replace.
NOTE:
You cannot measure the end gap on the
expander spacer of the oil control ring. If the oil
control ring rails show excessive gap, replace
all three rings.
End gap:
Standard
Top ring0.15 ~ 0.25 mm
(0.006 ~ 0.010 in)0.50 mm
(0.020 in)
2nd ring0.30 ~ 0.45 mm
(0.012 ~ 0.018 in)0.80 mm
(0.031 in)
Oil ring0.10 ~ 0.40 mm
(0.004 ~ 0.016 in)—

4 - 46
ENGCYLINDER AND PISTON
Piston pin
1. Inspect:
Piston pin
Blue discoloration/grooves → Replace,
then inspect the lubrication system.
2. Measure:
Piston pin-to-piston clearance
ASSEMBLY AND INSTALLATION
Piston ring and piston
1. Install:
Piston ring
Onto the piston.
NOTE:
Be sure to install the piston rings so that the
manufacturer’s marks or numbers are
located on the upper side of the rings.
Lubricate the piston and piston rings liberally
with engine oil. Measurement steps:
Measure 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)
Measure the inside diameter (piston) b.
Inside diameter (piston):
16.002 ~ 16.013 mm
(0.6300 ~ 0.6304 in)
Calculate 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
If 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 - 47
ENG

CYLINDER AND PISTON
2. Position:

Top ring

2nd ring

Oil ring
Offset the piston ring end gaps as
shown.
a
Top ring end
b
2nd ring end
c
Oil ring end (upper)
d
Oil ring
e
Oil 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

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

ENG
4 - 52
EMBRAYAGE
KUPPLUNG
FRIZIONE
Reibscheiben
1. Messen:
Reibscheibenstärke
Unvorschriftsmäßig → Die
Reibscheiben im Satz
erneuern.
Die Reibscheiben an vier
Stellen messen.
Kupplungsscheiben
1. Messen:
Verzug der Kupplungsschei-
ben
Unvorschriftsmäßig →
Kupplungsscheiben im Satz
erneuern.
Eine Richtplatte 1 und eine
Fühlerlehre 2 verwenden.
Reibscheibenstärke
2,9–3,1 mm
2,7 mm
Verzugsgrenze
0,1 mm
Druckhebel
1. Kontrollieren:
Druckhebelwelle 1
Verschleiß/Beschädigung →
Erneuern.
Druckstangen
1. Kontrollieren:
Druckstange 1 1
Lager 2
Unterlegscheibe 3
Druckstange 2 4
Kugel 5
Verschleiß/Beschädigung/
Verbiegung → Erneuern. Disque de friction
1. Mesurer:
Epaisseur de disque de friction
Hors-spécification → Changer
tous les disques de friction.
Mesurer chaque disque en qua-
tre endroits.
Disque d’embrayage
1. Mesurer:
Voile de disque d’embrayage
Hors spécification → Rampla-
cer tous les disques
d’embrayage.
Utiliser une plaque à surfacer
1 et une jauge d’épaisseur 2.
Epaisseur de disque de
friction:
2,9 à 3,1 mm
(0,114 à 0,122 in)
: 2,7 mm
(0,106 in)
Limite de déformation:
0,1 mm (0,004 in)
Levier de poussée
1. Contrôler:
Arbre de levier de poussée 1
Usure/endommagement →
Ramplacer.
Tige de poussée
1. Contrôler:
Tige de poussée 1 1
Roulement 2
Rondelle 3
Tige de poussée 2 4
Bille 5
Usure/endommagement/défor-
mation → Ramplacer.Disco conduttore
1. Misurare:
Spessore del disco conduttore
Fuori specifica → Sostituire in
blocco il disco conduttore.
Misurare tutti i quattro punti.
Disco condotto
1. Misurare:
Deformazione del disco con-
dotto
Fuori specifica → Sostituire in
blocco il disco condotto.
Utilizzare un piano di riscon-
tro 1 ed uno spessimetro 2.
Spessore del disco condut-
tore:
2,9 ~ 3,1 mm
(0,114 ~ 0,122 in)
: 2,7 mm
(0,106 in)
Limite di deformazione:
0,1 mm (0,004 in)
Alberino della leva spingente
1. Ispezionare:
Alberino della leva spingente
1
Usura/danno → Sostituire.
Asta di punteria
1. Ispezionare:
Asta di punteria 1 1
Cuscinetto 2
Rondella 3
Asta di punteria 2 4
Sfera 5
Usura/danno/flessioni → Sosti-
tuire.

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).
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.
Å
For USA and CDN
ı
Except 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 attenion to the differ-
ence 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