2002 YAMAHA TTR90 engine

CHAPTER 4
ENGINE
CARBURETOR ......................................... 4-1
CYLINDER HEAD ..................................... 4-8
CAMSHAFT AND ROCKER ARMS ....... 4-13
VALVES AND VALVE SPRINGS ........... 4-16
CYLINDER AND PISTON ....................... 4-21
CLUTCH .................................................. 4-27
KICK AXLE ............................................. 4-33
SHIFT SHAFT ......................................... 4-34
OIL PUMP ............................................... 4-36
CDI MAGNETO ....................................... 4-39
CRANKCASE AND CRANKSHAFT ....... 4-41
SHIFT FORK, SHIFT CAM AND
TRANSMISSION ..................................... 4-44
CHAPTER 5
CHASSIS
FRONT WHEEL AND REAR WHEEL ...... 5-1
FRONT FORK ........................................... 5-6
HANDLEBAR ............................................ 5-9
STEERING .............................................. 5-10
SWINGARM ............................................ 5-11
CHAPTER 6
ELECTRICAL
ELECTRICAL COMPONENTS AND
WIRING DIAGRAM ................................... 6-1
IGNITION SYSTEM ................................... 6-2
CARBURETOR HEATING SYSTEM ........ 6-6
MAINTENANCE RECORD ....................... 6-9

1 - 1
GEN
INFO
DESCRIPTION
EC100000
GENERAL INFORMATION
EC110000
DESCRIPTION
1“ENGINE STOP” button
2Front brake lever
3Throttle grip
4Fuel tank cap
5Kick starter
6Fuel tank
7Air cleaner
8Rear brake pedal
9Fuel cock
0Starter lever (choke)
ADrive chain
BShift pedal
CFront fork
NOTE:
lThe machine you have purchased may differ
slightly from those shown in the following.
lDesigns and specifications are subject to
change without notice.
1
1

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GEN
INFO
MACHINE IDENTIFICATION
EC120001
MACHINE IDENTIFICATION
There are two significant reasons for knowing
the serial number of your machine:
1. When ordering parts, you can give the
number to your Yamaha dealer for posi-
tive identification of the model you own.
2. If your machine is stolen, the authorities
will need the number to search for and
identify your machine.
EC121001
VEHICLE IDENTIFICATION NUMBER
The vehicle identification number 1 is
stamped on the right of the steering head pipe.
ENGINE SERIAL NUMBER
The engine serial number 1 is stamped into
the elevated part of the left-side of the engine.
EC124000
MODEL LABEL
The model label 1 is affixed to the frame
under the rider’s seat. This information will be
needed to order spare parts.
1

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GEN
INFO
IMPORTANT INFORMATION
EC132000
ALL REPLACEMENT PARTS
1. We recommend to use Yamaha genuine
parts for all replacements. Use oil and/or
grease recommended by Yamaha for
assembly and adjustment.
EC133000
GASKETS, OIL SEALS AND O-RINGS
1. All gaskets, oil seals, and O-rings should
be replaced when an engine is over-
hauled. All gasket surfaces, oil seal lips,
and O-rings must be cleaned.
2. Properly oil all mating parts and bearings
during reassembly. Apply grease to the
oil seal lips.
EC134000
LOCK WASHERS/PLATES AND COTTER
PINS
1. All lock washers/plates 1 and cotter pins
must be replaced when they are
removed. Lock tab(s) should be bent
along the bolt or nut flat(s) after the bolt
or nut has been properly tightened.
EC135001
BEARINGS AND OIL SEALS
1. Install the bearing(s) 1 and oil seal(s) 2
with their manufacturer’s marks or num-
bers facing outward. (In other words, the
stamped letters must be on the side
exposed to view.) When installing oil
seal(s), apply a light coating of light-
weight lithium base grease to the seal
lip(s). Oil the bearings liberally when
installing.
CAUTION:
Do not use compressed air to spin the
bearings dry. This causes damage to the
bearing surfaces.

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GEN
INFO
SPECIAL TOOLS
SPECIAL TOOLS
The proper special tools are necessary for complete and accurate tune-up and assembly. Using the
correct special tool will help prevent damage caused by the use of improper tools or improvised
techniques. The shape and part number used for the special tool differ by country, so two types are
provided. Refer to the list provided to avoid errors when placing an order.
NOTE:
lFor U.S.A. and Canada, use part number starting with “YM-”, “YU-”, “YS-” or “ACC-”.
lFor others, use part number starting with “90890-”.
Part number Tool name/How to use Illustration
YU-1083-A
90890-01084
90890-01085Slide hammer set
Weight
Slide hammer bolt
These tools are used when removing or installing the
rocker arm shafts.YU-1083-A 90890-01084
90890-01085
YU-1268, 90890-01268 Ring nut wrench
This tool is used when loosen the steering ring nut to
specification.YU-1268 90890-01268
YU-3112-C, 90890-03112 Pocket tester
Use this tool to inspect the coil resistance, output
voltage and amperage.YU-3112-C 90890-03112
YU-8036-B
90890-03113Inductive tachometer
Engine tachometer
This tool is needed for observing engine rpm.YU-8036-B 90890-03113
YM-4019, 90890-04019 Valve spring compressor
This tool is needed to remove and install the valve
assemblies.YM-4019 90890-04019
YM-1300
90890-01294Damper rod holder set
Damper rod holder
Use this tool to remove and install the damper rod.YM-1300 90890-01294
YU-1304, 90890-01304 Piston pin puller set
This tool is used to remove the piston pin.YU-1304 90890-01304

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GEN
INFO
CONTROL FUNCTIONS
EC150000
CONTROL FUNCTIONS
“ENGINE STOP” SWITCH
Make sure that the engine stop switch 1 is
positioned to “ ”. The engine stop switch has
been equipped to ensure safety in an emer-
gency such when the machine is up set or
trouble takes place in the throttle system. The
engine will not start or run when the engine
stop switch is turned to “ ”.
SHIFT PEDAL
The gear ratios of the constant-mesh 3 speed
transmission are ideally spaced. The gears
can be shifted by using the shift pedal 1 on
the left side of the engine.
WARNING
When starting out on the machine, shift the
transmission into 1st after pulling in the
front brake lever and closing the throttle
grip.
KICK STARTER
WARNING
Before starting the engine, be sure to shift
the transmission into neutral.
Rotate the kick starter 1 away from the
engine. Push the starter down lightly with your
foot until the gears engage, then kick smoothly
and forcefully to start the engine.
EC155001
THROTTLE GRIP
The throttle grip 1 is located on the right han-
dlebar; it accelerates or decelerates the
engine. For acceleration, turn the grip toward
you; for deceleration, turn it away from you.

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GEN
INFO
CONTROL FUNCTIONS
EC156000
FRONT BRAKE LEVER
The front brake lever 1 is located on the right
handlebar. Pull it toward the handlebar to acti-
vate the front brake.
EC157000
REAR BRAKE PEDAL
The rear brake pedal 1 is located on the right
side of the machine. Press down on the brake
pedal to activate the rear brake.
FUEL COCK
The fuel cock supplies fuel from the tank to
carburetor while filtering the fuel. The fuel cock
has the three positions:
OFF: With the lever in this position, fuel will
not flow. Always return the lever to this
position when the engine is not running.
ON: With the lever in this position, fuel flows
to the carburetor. Normal riding is done
with the lever in this position.
RES: This indicates reserve. If you run out of
fuel while riding, move the lever to this
position. FILL THE TANK AT THE
FIRST OPPORTUNITY. BE SURE TO
SET THE LEVER TO “ON” AFTER
REFUELING.
STARTER LEVER (CHOKE)
When cold, the engine requires a richer air/fuel
mixture for starting. A separate starter circuit,
which is controlled by the starter lever 1, sup-
plies this mixture.
Pull the lever out to open the circuit (for start-
ing) and push the lever in to close the circuit.

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GEN
INFO
CONTROL FUNCTIONS/FUEL
FUEL TANK CAP
Remove the fuel tank cap 1 by turning
counter-clockwise.
WARNING
Do not overfill the fuel tank. Avoid spilling
fuel on the hot engine.
FUEL
Use regular gasoline. Always use fresh, name
brand gasoline.
WARNING
Do not overfill the fuel tank. Avoid spilling
fuel on the hot engine. Do not fill the fuel
tank above the bottom of the filler tube 1
as shown in the illustration or it may over-
flow when the fuel heats up later and
expands.
aFuel level
CAUTION:
Use only unleaded gasoline. The use of
leaded gasoline will cause severe damage
to the engine internal parts such as valves,
piston rings, and exhaust system, etc.
Recommended fuel:
For USA, AUS and NZ:
Unleaded gasoline only
For CDN and EUROPE:
Regular unleaded gasoline
only
For ZA:
Regular gasoline
Fuel tank capacity:
Total:
4.2 L (0.92 lmp gal, 1.11 US gal)
Reserve:
0.5 L (0.11 lmp gal, 0.13 US gal)