2000 YAMAHA TTR90 engine oil

4 - 25
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 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)
lMeasure the piston inside diameter b.
lCalculate the piston pin-to-piston clear-
ance with the following formula.
Piston pin-to-piston clearance =
Bore size (piston pin) b –
Outside diameter (piston pin) a
lIf out of specification, replace the piston.
Piston pin-to-piston clearance:
0.002 ~ 0.017 mm
(0.00008 ~ 0.00067 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 - 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:
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.

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
ENGCRANKCASE AND CRANKSHAFT
CRANKCASE AND CRANKSHAFT
Extent of removal Order Part name Q’ty Remarks
CRANKCASE SEPARATION
AND CRANKSHAFT REMOVAL
Preparation for removal Seat and fuel tank
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
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.

5 - 1
CHAS

EC500000
CHASSIS
FRONT WHEEL AND REAR WHEEL
EC598000
FRONT WHEEL AND FRONT BRAKE
FRONT WHEEL AND REAR WHEEL
Extent of removal:
1
Front wheel removal
2
Wheel bearing removal
3
Brake shoe plate assembly removal and disassembly
Extent of removal Order Part name Q’ty Remarks
FRONT WHEEL REMOVAL
Preparation for removal Hold the machine by placing the
suitable stand under the engine.
1 Bolt (brake cable holder) 1 Only loosening.
2 Brake cable 1 Disconnect at the lever side.
3 Wheel axle nut 1
4 Front wheel axle 1
5 Front wheel 1
6 Collar set 1
7 Brake shoe plate assembly 1
8 Oil seal 1
9Bearing
2Refer to “REMOVAL POINTS”.
WARNING
Support the machine securely so there is nodanger of it falling over.
2
31
3

5

6 - 1
–+ELEC

ELECTRICAL COMPONENTS AND WIRING DIAGRAM
EC600000
ELECTRICAL
EC610000
ELECTRICAL COMPONENTS AND WIRING DIAGRAM
EC611000
ELECTRICAL COMPONENTS
1
CDI magneto
2
CDI unit
3
Ignition coil
4
Spark plug
5
“ENGINE STOP” switch
6
Thermo switch
7
Carburetor heater
8
Rectifier/regulator
COLOR CODE
B...................... Black
Br .................... Brown
G ..................... Green
O ..................... Orange
R ..................... Red
W..................... White
EC612000
WIRING DIAGRAM
G/WB/RW/LW/RBr G
RW
WB
Y/R
O
BO
B
B
BY/RY
WY/RB
W
Y
B
GG/W
B/W
B/W
BrB/RWWWY
OO
BBW/LY/RR
W
B
B
B
W/R
Y/R
OFF
RUN
B
Y/R
B
B
Y
Y
1
23
4
5 6
7 8

B/R ................... Black/Red
B/W .................. Black/White
G/W.................. Green/White
W/L .................. White/Blue
W/R .................. White/Red
6

–+ELEC

6 - 2
IGNITION SYSTEM
EC620000
IGNITION SYSTEM
EC621001
INSPECTION STEPS
Use the following steps for checking the possibility of the malfunctioning engine being attributable to
ignition system failure and for checking the spark plug which will not spark.
NOTE:

l
Remove the following parts before inspection.
1) Seat
2) Fuel tank
l
Use the following special tools in this inspection.
Spark gap testClean or replace
spark plug.
Check entire ignition
system for connection.Repair or replace.
Check “ENGINE STOP”
switch.Replace.
Check ignition coil. Primary coil Replace.
Secondary coilReplace.
Check CDI magneto. Pickup coil Replace.
Source coil Replace.
Replace CDI unit.
Dynamic spark tester:
YM-34487
Ignition checker:
90890-06754
Pocket tester:
YU-03112/90890-03112
No Spark
OK
OK
OK
OK
Spark
No good
No good
No good
No good
No good
No good