oil YAMAHA YZ426F 2000 Workshop Manual

4 - 31
ENGVALVES AND VALVE SPRINGS
Measurement steps:
lApply Mechanic’s blueing dye (Dykem) b
to the valve face.
lInstall the valve into the cylinder head.
lPress the valve through the valve guide
and onto the valve seat to make a clear
pattern.
lMeasure the valve seat width. Where the
valve seat and valve face made contact,
blueing will have been removed.
lIf the valve seat is too wide, too narrow, or
the seat is not centered, the valve seat
must be refaced.
9. Lap:
lValve face
lValve 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:
lApply a coarse lapping compound to the
valve face.
lApply molybdenum disulfide oil to the
valve stem.
lInstall the valve into the cylinder head.
lTurn the valve until the valve face and
valve seat are evenly polished, then clean
off all of the compound.
lApply a fine lapping compound to the
valve face and repeat the above steps.
CAUTION:
Do not let the compound enter the gap
between the valve stem and the guide.
NOTE:
For best lapping results, lightly tap the valve
seat while rotating the valve back and forth
between your hands.

4 - 33
ENGVALVES AND VALVE SPRINGS
Valve lifter
1. Inspect:
lValve lifter
Scratches/damage ® Replace both lift-
ers and cylinder head.
ASSEMBLY AND INSTALLATION
1. Apply:
lMolybdenum disulfide oil
Onto the valve stem and valve stem
seal.
2. Install:
lValves 1
lValve spring seats 2
lValve stem seals 3
lValve springs 4
lValve spring retainers 5
NOTE:
lMake sure that each valve is installed in its
original place, also referring to the embossed
mark as follows.
Intake (right/left): “5BE”
Intake (middle): “5BE”
Exhaust: “5BE”
lInstall the valve springs with the larger pitch
a facing upwards.
bSmaller pitch
3. Install:
lValve cotters
NOTE:
While compressing the valve spring with a
valve spring compressor 1 and attachment 2
install the valve cotters.
Valve spring compressor:
YM-04019/90890-04019
Attachment:
YM-04108/90890-04108
New

4 - 34
ENGVALVES AND VALVE SPRINGS
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.
5. Install:
lAdjusting pad 1
lValve lifter 2
NOTE:
lLubricate the valve lifters and pads with
molybdenum disulfide oil.
lValve lifter must turn smoothly when rotated
with a finger.
lBe careful to reinstall valve lifters and pads
in their original place.

4 - 38
ENGCYLINDER AND PISTON
Piston ring
1. Measure:
lRing 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:
lPiston 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)
3. Measure:
lRing 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.
Side clearance:
Standard
Top
ring0.030 ~ 0.065 mm
(0.0012 ~ 0.0026 in)0.13 mm
(0.005 in)
2nd
ring0.020 ~ 0.055 mm
(0.0008 ~ 0.0022 in)0.13 mm
(0.005 in)
End gap:
Standard
Top
ring0.20 ~ 0.30 mm
(0.008 ~ 0.012 in)0.55 mm
(0.022 in)
2nd
ring0.35 ~ 0.50 mm
(0.014 ~ 0.020 in)0.85 mm
(0.033 in)
Oil
ring0.20 ~ 0.50 mm
(0.01 ~ 0.02 in)—

4 - 39
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
Measurement steps:
lMeasure the outside diameter (piston pin)
a.
If out of specification, replace the piston
pin
Outside diameter (piston pin):
18.991 ~ 19.000 mm
(0.7477 ~ 0.7480 in)
lMeasure the inside diameter (piston) b.
Inside diameter (piston):
19.004 ~ 19.015 mm
(0.7482 ~ 0.7486 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:
0.009 ~ 0.025 mm
(0.00035 ~ 0.00098 in)
: 0.07 mm (0.003 in)
ASSEMBLY AND INSTALLATION
Piston
1. Install:
lPiston rings
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.

4 - 40
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 clips 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.
4. Lubricate:
lPiston
lPiston rings
lCylinder
NOTE:
Apply a liberal coating of engine oil.
New
Cylinder
1. Install:
lGasket 1
lCylinder 2
NOTE:
Install the cylinder with one hand while com-
pressing the piston rings with the other hand.
CAUTION:
lPass the timing chain 3 through the tim-
ing chain cavity.
lBe careful not to damage the timing chain
damper 4 during installation.
New

ENG

4 - 41
CLUTCH
CLUTCH
CLUTCH
Extent of removal:
1
Push rod and push lever removal
2
Push pod 1 disassembly
3
Friction plate and clutch plate removal
4
Clutch housing 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 Gasket 1
3 Dowel pin 2
4 Clutch spring 6
5 Pressure plate 1
6 Push rod 1 1
7 Circlip 1
8 Plain washer 1
9 Bearing 1
10 Push rod 2 1
4
1
1
2
3

4 - 44
ENG

CLUTCH
EC484500
Friction plate
1. Measure:
l
Friction plate thickness
Out of specification
®
Replace friction
plate as a set.
Measure at all four points.
EC484600
Clutch plate
1. Measure:
l
Clutch plate warpage
Out of specification
®
Replace clutch
plate as a set.
Use a surface plate
1
and thickness
gauge
2
.
Push lever
1. Inspect:
l
Push lever
1

Wear/damage
®
Replace.
Friction plate thickness:
2.9 ~ 3.1 mm
(0.114 ~ 0.122 in)
: 2.7 mm (0.106 in)
Warp limit:
0.1 mm (0.004 in)
EC484810
Push rod
1. Inspect:
l
Push rod 1
1

l
Bearing
2

l
Plain washer
3

l
Push rod 2
4

Wear/damage/bend
®
Replace.
EC495000
ASSEMBLY AND INSTALLATION
Push lever
1. Install:
l
Push lever
1

NOTE:

Apply the engine oil on the oil seal lip and push
lever.

4 - 44
ENG
EMBRAYAGE
KUPPLUNG
Reibscheiben
1. Messen:
lReibscheibenstärke
Unvorschriftsmäßig ® Die Reibschei-
ben im Satz erneuern.
Die Reibscheiben an vier Stellen mes-
sen.
Kupplungsscheiben
1. Messen:
lVerzug der Kupplungsscheiben
Unvorschriftsmäßig ® Kupplungsschei-
ben im Satz erneuern.
Eine Richtplatte 1 und eine Fühlerleh-
re 2 verwenden.
Druckhebel
1. Kontrollieren:
lDruckhebel 1
Verschleiß/Beschädigung ® Erneuern.
Reibscheibenstärke
2,9–3,1 mm
2,7 mm
Verzugsgrenze
0,1 mm
Druckstangen
1. Kontrollieren:
lDruckstange 1 1
lLager 2
lBeilagscheibe 3
lDruckstange 2 4
Verschleiß/Beschädigung/Verbiegung
® Erneuern.
ZUSAMMENBAU UND MONTAGE
Druckhebel
1. Montieren:
lDruckhebel 1
HINWEIS:
Lithiumfett auf Dichtringlippe und Druckhebel
auftragen. Disque de friction
1. Mesurer:
lEpaisseur de disque de friction
Hors-spécification ® Changer tous les dis-
ques de friction.
Mesurer chaque disque en quatre endroits.
Disque d’embrayage
1. Mesurer:
lVoile de disque d’embrayage
Hors-spécification ® Changer tous les dis-
ques d’embrayage.
Utiliser une plaque à surfacer 1 et une
jauge d’épaisseur 2.
Levier de poussée
1. Contrôler:
lLevier de poussée 1
Usure/endommagement ® Changer.
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)
Tige de poussée
1. Contrôler:
lTige de poussée 1 1
lRoulement 2
lRondelle ordinaire 3
lTige de poussée 2 4
Usure/endommagement/déformation ®
Changer.
ASSEMBLAGE ET MONTAGE
Levier de poussée
1. Monter:
lLevier de poussée 1
N.B.:
Appliquer de la graisse à base de savon de lithium
sur le joint à lèvre et le levier de poussée.

4 - 45
ENG

CLUTCH
EC495221
Clutch
1. 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
New
T R..75 Nm (7.5 m · kg, 54 ft · lb)
õ
2. Bend the lock washer 1 tab.
3. Install:
lFriction plate 1
lClutch plate 2
NOTE:
lInstall the clutch plates and friction plates
alternately on the clutch boss, starting with a
friction plate and ending with a friction plate.
lApply the engine oil on the friction plates and
clutch plates.
4. Install:
lBearing 1
lPlain washer 2
lCirclip 3
To push rod 1 4.
NOTE:
Apply the engine oil on the bearing and plain
washer.
New