2002 YAMAHA TTR90 oil

4 - 15
ENGCAMSHAFT AND ROCKER ARMS
3. Apply:
lMolybdenum disulfide oil
(onto the rocker arm and rocker arm
shaft)
4. Install:
lRocker arm 1
lRocker arm shaft 2

4 - 19
ENGVALVES AND VALVE SPRINGS
2. 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.
CAUTION:
Do not let the compound enter the gap
between the valve stem and the guide.
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.
NOTE:
For best lapping results, lightly tap the valve
seat while rotating the valve back and forth
between your hands.
lApply 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.
lApply Mechanic’s blueing dye (Dykem) 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 again. If the
valve seat width is out of specification,
reface and relap the valve seat.

4 - 20
ENGVALVES AND VALVE SPRINGS
ASSEMBLY AND INSTALLATION
1. Apply:
lMolybdenum disulfide oil
(onto the valve stem and valve stem
seal)
2. Install:
lValve stem seats
lValves
lValve springs
lValve spring retainers
NOTE:
lMake sure that each valve is installed in its
original place, also referring to the embossed
mark as follows.
Intake: “G”
Exhaust: “L”
lInstall the valve springs with the larger pitch
a facing upwards.
bSmaller pitch
New
3. Install:
lValve cotters
NOTE:
While compressing the valve spring with a
valve spring compressor and attachment 1
install the valve cotters.
Valve spring compressor:
YM-4019/90890-04019
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.

4 - 24
ENGCYLINDER AND PISTON
Piston ring
1. Measure:
lRing side clearance
Use a feeler gauge.
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 5 mm (0.20 in) into the cylinder.
Push the ring with the piston crown so that the
ring will be at a right angle to the cylinder bore.
a5 mm (0.20 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 Limit
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)
End gap
Standard Limit
Top ring0.10 ~ 0.25 mm
(0.004 ~ 0.010 in)0.4 mm
(0.016 in)
2nd ring0.10 ~ 0.25 mm
(0.004 ~ 0.010 in)0.4 mm
(0.016 in)
Oil ring0.2 ~ 0.7 mm
(0.01 ~ 0.03 in)—

4 - 25
ENGCYLINDER AND PISTON
Piston pin
1. Inspect:
lPiston pin
Blue discoloration/grooves ®
Replace, then inspect the lubrication
system.
2. Measure:
lPiston pin outside diameter
lPiston pin bore inside diameter
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. Measurement steps:
lMeasure the piston pin outside diameter
a.
If out of specification, replace the piston
pin
Outside diameter (piston pin):
12.996 ~ 13.000 mm
(0.5117 ~ 0.5118 in)
:12.976 mm (0.5109 in)
lMeasure the piston inside diameter b.
If out of specification, replace the piston.
Inside diameter (piston):
13.002 ~ 13.013 mm
(0.5119 ~ 0.5123 in)
: 13.045 mm (0.5136 in)

4 - 26
ENGCYLINDER AND PISTON
2. Position:
lTop ring
l2nd ring
lOil ring
Offset the piston ring end gaps as
shown.
aTop ring end
bOil ring end (lower)
cOil ring end (upper)
d2nd ring end
3. Install:
lPiston 1
lPiston pin 2
lPiston pin clips 3
NOTE:
lApply engine oil onto the piston pin, piston
ring and piston.
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:
lDowel pins
lGasket
lCylinder 1
NOTE:
Install the cylinder with one hand while com-
pressing the piston rings with the other hand.
CAUTION:
lBe careful not to damage the timing chain
damper during installation.
lPass the timing chain through the timing
chain cavity.
New

4 - 27
ENGCLUTCH
CLUTCH
CRANKCASE COVER (LEFT AND RIGHT)
Extent of removal:1 Crankcase cover (left) removal2 Crankcase cover (right) removal
Extent of removal Order Part name Q’ty Remarks
CRANKCASE COVER (LEFT
AND RIGHT) REMOVAL
Preparation for removal Drain the engine oil. Refer to “ENGINE OIL REPLACEMENT”
section in the CHAPTER 3.
1 Shift pedal 1
2 Drive sprocket cover 1
3 Crankcase cover (left) 1
4 Gasket 1
5 Dowel pin 2
6 Clutch adjusting screw 1
7 Kick crank 1
8 Crankcase cover (right) 1
9 Gasket 1
10 Dowel pin 2
1
2

4 - 31
ENG
EMBRAYAGE
KUPPLUNG
Kupplungsscheiben
1. Messen:
lVerzug der Kupplungsscheiben
Unvorschriftsmäßig ® Kupplungsschei-
ben im Satz erneuern.
Eine Richtplatte 1 und eine Fühlerleh-
re 2 verwenden.
Kupplungsfeder
1. Messen:
lUngespannte Länge der Kupplungsfe-
der a
Unvorschriftsmäßig ® Die Feder im
Satz erneuern.
Druckstange
1. Messen:
lVerzug (Druckstange Nr. 2)
Unvorschriftsmäßig ® Erneuern.
Grenzwert
0,2 mm
Ungespannte Länge der Kupp-
lungsfeder
Standard Grenzwert
26,2 mm 24,2 mm
Druckstangen-Verzugsgrenze
0,5 mm
Primärkupplung
1. Messen:
lPrimärkupplungsgehäuse-Innendurch-
messer
Unvorschriftsmäßig ® Erneuern.
Primärkupplungsgehäuse-Innen-
durchmesser
105 mm
106 mm
2. Messen:
lTiefe a der Kupplungsbelag-Nut
Unvorschriftsmäßig ® Erneuern.
Tiefe der Kupplungsbelag-Nut
1,0–1,3 mm
0,1 mm
Disques 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.
Ressorts d’embrayage
1. Mesurer:
lLongueur libre de ressort d’embrayage a
Hors spécification ® Changer tous les res-
sorts.
Tige de commande
1. Mesurer:
lDéformation (tige de commande n˚2)
Hors spécifications ® Remplacer.
Limite de déformation:
0,2 mm (0,008 in)
Longueur libre de ressort
d’embrayage
Standard Limite
26,2 mm
(1,03 in)24,2 mm
(0,95 in)
Limite de déformation:
0,5 mm (0,02 in)
Embrayage primaire
1. Mesurer:
lDiamètre intérieur de cloche d’embrayage
primaire
Hors spécifications ® Remplacer.
Diamètre intérieur de cloche
d’embrayage primaire:
105 mm (4,13 in)
: 106 mm (4,17 in)
2. Mesurer:
lProfondeur de gorge de garniture d’embra-
yage a
Hors spécifications ® Remplacer.
Profondeur de gorge de garniture
d’embrayage:
1,0 à 1,3 mm (0,039 à 0,051 in)
: 0,1 mm (0,004 in)