2001 YAMAHA TTR90 engine

4 - 11
ENG

CYLINDER HEAD
4. Remove:
l
Cylinder head
NOTE:

l
Loosen the bolts and nuts in their proper
loosening sequence.
l
Start by loosening each bolt and nut 1/2 turn
until all are loose.
ASSEMBLY AND INSTALLATION
1. Install:
l
Cylinder head
2. Tighten:
l
Nuts
l
Bolts
NOTE:

l
Apply the engine oil on the contact surfaces
of the nuts, bolts and copper washers.
l
Follow the numerical order shown in the illus-
tration. Tighten the bolts and nuts in two
stages.
T R..22 Nm (2.2 m · kg, 16 ft · lb)
T R..10 Nm (1.0 m · kg, 7.2 ft · lb)

3. Install:
l
Camshaft sprocket
1

Installation steps:
l
Turn the crankshaft counterclockwise until
the “I” mark
a
on the rotor is aligned with
the stationary pointer
b
on the crankcase
cover.
l
Align the “I” mark
c
on the camshaft
sprocket with the stationary pointer
d
on
the cylinder head.
l
Fit the timing chain
2
onto camshaft
sprocket and install the camshaft sprocket
on the camshaft.
NOTE:
When installing the camshaft sprocket,
keep the timing chain as tense as possible
on the exhaust side.

4 - 14
ENGCAMSHAFT AND ROCKER ARMS
REMOVAL POINTS
Rocker arm shaft
1.Remove:
lRocker arm shafts
NOTE:
Use a slide hammer bolt 1 and weight 2 to
slide out the rocker arm shafts.
Slide hammer set:
YU-1083-A
Slide hammer bolt:
90890-01085
Weight:
90890-01084
INSPECTION
Camshaft
1.Measure:
lCam lobes length a and b
Out of specification ® Replace.
Cam lobes length limit:
Intake:
a 25.328 mm (0.9972 in)
b 20.934 mm (0.8242 in)
Exhaust:
a 25.186 mm (0.9916 in)
b 20.947 mm (0.8247 in)
ASSEMBLY AND INSTALLATION
1.Apply:
lMolybdenum disulfide oil
(onto the camshaft cam lobe)
lEngine oil
(onto the camshaft bearing)
2.Install:
lCamshaft 1

4 - 25
ENG

CYLINDER AND PISTON
Piston pin
1. Inspect:
l
Piston pin
Blue discoloration/grooves
®

Replace, then inspect the lubrication
system.
2. Measure:
l
Piston pin outside diameter
l
Piston pin bore inside diameter
Measurement steps:
l
Measure 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)
l
Measure 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)
ASSEMBLY AND INSTALLATION
Piston
1. Install:
l
Piston rings
(onto the piston)
NOTE:

l
Be sure to install the piston rings so that the
manufacturer’s marks or numbers are
located on the upper side of the rings.
l
Lubricate the piston and piston rings liberally
with engine oil.

4 - 26
ENG

CYLINDER AND PISTON
2. Position:
l
Top ring
l
2nd ring
l
Oil ring
Offset the piston ring end gaps as
shown.
a
Top ring end
b
Oil ring end (lower)
c
Oil ring end (upper)
d
2nd ring end
3. Install:
l
Piston
1

l
Piston 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 - 41
ENG

CRANKCASE AND CRANKSHAFT
CRANKCASE AND CRANKSHAFT
Extent of removal Order Part name Q’ty Remarks
CRANKCASE SEPARATION
AND CRANKSHAFT REMOVAL
Preparation for removal Seat, fuel tank and rear fender
Exhaust pipe
Air filter case
Carburetor Refer to “CARBURETOR” section.
Drain the engine oil Refer to “ENGINE OIL REPLACEMENT”
section in the CHAPTER 3.
Engine guard and drive sprocket
Engine assembly From the chassis.
Cylinder head Refer to “CYLINDER HEAD” section.
Cylinder and piston Refer to “CYLINDER AND PISTON” sec-
tion.
Clutch housing and clutch carrier Refer to “CLUTCH” section.
Kick axle assembly Refer to “KICK AXLE” section.

4 - 44
ENG

SHIFT FORK, SHIFT CAM AND TRANSMISSION
SHIFT FORK, SHIFT CAM AND TRANSMISSION
Extent of removal:
1
Shift fork, shift cam, main axle and drive axle removal
2
Main axle disassembly
3
Drive axle disassembly
Extent of removal Order Part name Q’ty Remarks
SHIFT FORK, SHIFT CAM
TRANSMISSION REMOVAL
Preparation for removal Engine assembly
Separate the crankcase. Refer to “CRANKCASE AND CRANK-
SHAFT” section.
1 Guide bar 1
2 Shift cam 1
Refer to “REMOVAL POINTS”. 3 Shift fork 2 “R” 1
4 Shift fork 1 “L” 1
5 Drive axle assembly 1
6 Main axle assembly 1
7 2nd pinion gear 1
8 Circlip 1
9 Washer 1
1
2

4 - 46
ENG

SHIFT FORK, SHIFT CAM AND TRANSMISSION
EC4H3000
REMOVAL POINTS
Shift fork, shift cam and transmission
1. Remove:
l
Shift forks
l
Shift cam
l
Drive axle assembly
l
Main axle assembly
NOTE:

l
Tap lightly on the transmission drive axle and
shift cam with a soft hammer to remove.
l
Remove assembly carefully. Note the posi-
tion of each part. Pay particular attention to
the location and direction of shift forks.
ASSEMBLY AND INSTALLATION
Transmission, shift cam shift fork
1. Install:
l
Main axle assembly
1

l
Drive axle assembly
2

2. Install:
l
Shift fork 1 “L”
1

l
Shift fork 2 “R”
2

l
Shift cam
3

l
Guide bar
4

NOTE:

The embossed marks on the shift forks should
face towards the right side of the engine and
be in the following sequence: “R”, “L”.
3. Check:
l
Shifter operation
l
Transmission operation
Unsmooth operation
®
Repair.