2000 YAMAHA YZ426F oil

4 - 26
ENG
CULASSE
ZYLINDERKOPF
PRÜFUNG
Zylinderkopf
1. Entfernen:
lÖlkohleablagerungen (im Brennraum)
Einen abgerundeten Schaber verwen-
den.
HINWEIS:
Keine scharfkantigen Gegenstände benutzen,
um Beschädigungen und Kratzer an folgenden
Stellen zu vermeiden:
lZündkerzenbohrung
lVentilsitze
2. Kontrollieren:
lZylinderkopf
Kratzer/Beschädigungen ® Erneuern.
3. Messen:
lZylinderkopf-Verzug
Grenzwert überschritten ® Planschlei-
fen.
ZUSAMMENBAU UND MONTAGE
1. Montieren:
lZylinderkopf
lSchrauben (1–4)
lSchraube (5)
lMuttern (6, 7)
lMuttern (8, 9)
HINWEIS:
Die numerierte Reihenfolge laut Abbildung befol-
gen. Schrauben und Muttern in zwei Arbeits-
schritten festziehen.
Zylinderkopf-Verzugsgrenze
unter 0,03 mm
Arbeitsschritte
lLineal und Fühlerlehre über den Zylinder-
kopf legen.
lVerzug mit der Fühlerlehre messen.
lIst die Verzugsgrenze überschritten, den
Zylinderkopf planschleifen.
lDen Zylinderkopf mit Naßschleifpapier (Kör-
nung 400–600) auf einer planen Platte in
einer Achterbewegung abschleifen.
HINWEIS:
Den Zylinderkopf mehrmals drehen, um
eine ebene Oberfläche zu gewährleisten.
T R..44 Nm (4,4 m · kg)
T R..10 Nm (1,0 m · kg)
T R..20 Nm (2,0 m · kg)
T R..10 Nm (1,0 m · kg)
CONTROLE
Culasse
1. Eliminer:
lDépôt de calamine
(de la chambre de combustion)
Utiliser un grattoir arrondi.
N.B.:
Ne pas utiliser d’instrument pointu pour éviter
d’endommager ou de rayer:
lFilets de bougies
lSièges de soupape
2. Contrôler:
lCulasse
Rayures/endommagement ® Remplacer.
3. Mesurer:
lDéformation de la culasse
Hors spécifications ® Surfacer.
ASSEMBLAGE ET MONTAGE
1. Monter:
lCulasse
lBoulon (1 à 4)
lBoulon (5)
lEcrou (6, 7)
lEcrou (8, 9)
N.B.:
Suivre l’ordre numérique montré sur l’illustration.
Serrer les boulons et les écrous en deux étapes.
Limite de déformation de la culasse:
Moins de 0,03 mm (0,002 in)
Etapes de la mesure de la limite de déforma-
tion et du surfaçage:
lPlacer une règle et une jauge d’épaisseur sur la
culasse.
lUtiliser une jauge d’épaisseur pour mesurer la
déformation.
lSi la déformation est hors spécifications, surfa-
cer la culasse.
lMettre un morceau de toile émeri n˚ 400 à 600
humide sur une plaque à surfacer et surfacer la
culasse en décrivant des “huit”.
N.B.:
Tourner la culasse plusieurs fois pour obtenir
une surface lisse.
T R..44 Nm (4,4 m · kg, 32 ft · lb)
T R..10 Nm (1,0 m · kg, 7,2 ft · lb)
T R..20 Nm (2,0 m · kg, 14 ft · lb)
T R..10 Nm (1,0 m · kg, 7,2 ft · lb)

4 - 30
ENGVALVES AND VALVE SPRINGS
3. Inspect:
lValve face
Pitting/wear ® Grind the face.
lValve stem end
Mushroom shape or diameter larger
than the body of the stem ® Replace.
4. Measure:
lMargin thickness a
Out of specification ® Replace.
5. Measure:
lRunout (valve stem)
Out of specification ® Replace.
NOTE:
lWhen installing a new valve always replace
the guide.
lIf the valve is removed or replaced always
replace the oil seal.
6. Eliminate:
lCarbon deposits
(from the valve face and valve seat)
7. Inspect:
lValve seats
Pitting/wear ® Reface the valve seat.
8. Measure:
lValve seat width a
Out of specification ® Reface the valve
seat.
Margin thickness:
Intake:
1.0 mm (0.039 in)
: 0.85 mm (0.033 in)
Exhaust:
1.0 mm (0.039 in)
: 0.85 mm (0.033 in)
Runout limit:
0.01 mm (0.0004 in)
Valve seat width:
Intake:
0.9 ~ 1.1 mm (0.0354 ~ 0.0433 in)
: 1.5 mm (0.06 in)
Exhaust:
0.9 ~ 1.1 mm (0.0354 ~ 0.0433 in)
: 1.5 mm (0.06 in)
NOTE:
After replacing the valve guide reface the
valve seat.

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