2003 YAMAHA TTR90 oil

4 - 11
ENGCYLINDER HEAD
4. Remove:
Cylinder head
NOTE:
Loosen the bolts and nuts in their proper
loosening sequence.
Start by loosening each bolt and nut 1/2 turn
until all are loose.
ASSEMBLY AND INSTALLATION
1. Install:
Cylinder head
2. Tighten:
Nuts
Bolts
NOTE:
Apply the engine oil on the contact surfaces
of the nuts, bolts and copper washers.
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:
Camshaft sprocket 1
Installation steps:
Turn the crankshaft counterclockwise until
the “I” mark a on the rotor is aligned with
the stationary pointer b on the crankcase
cover.
Align the “I” mark c on the camshaft
sprocket with the stationary pointer d on
the cylinder head.
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.

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ENGCAMSHAFT AND ROCKER ARMS
REMOVAL POINTS
Rocker arm shaft
1. Remove:
Rocker 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:
Cam lobes length a and b
Out of specification → Replace.
Cam lobes length limit:
Intake:
a 25.398 mm (0.9999 in)
b 21.004 mm (0.8269 in)
Exhaust:
a 25.256 mm (0.9943 in)
b 21.017 mm (0.8274 in)
ASSEMBLY AND INSTALLATION
1. Apply:
Molybdenum disulfide oil
(onto the camshaft cam lobe)
Engine oil
(onto the camshaft bearing)
2. Install:
Camshaft 1

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ENGCAMSHAFT AND ROCKER ARMS
3. Apply:
Molybdenum disulfide oil
(onto the rocker arm and rocker arm
shaft)
4. Install:
Rocker arm 1
Rocker arm shaft 2

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ENGVALVES AND VALVE SPRINGS
2. Lap:
Valve face
Valve 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:
Apply a coarse lapping compound to the
valve face.
CAUTION:
Do not let the compound enter the gap
between the valve stem and the guide.
Apply molybdenum disulfide oil to the
valve stem.
Install the valve into the cylinder head.
Turn 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.
Apply 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.
Apply Mechanic’s blueing dye (Dykem) to
the valve face.
Install the valve into the cylinder head.
Press the valve through the valve guide
and onto the valve seat to make a clear
pattern.
Measure the valve seat width again. If the
valve seat width is out of specification,
reface and relap the valve seat.

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ENGVALVES AND VALVE SPRINGS
ASSEMBLY AND INSTALLATION
1. Apply:
Molybdenum disulfide oil
(onto the valve stem and valve stem
seal)
2. Install:
Valve stem seats
Valves
Valve springs
Valve spring retainers
NOTE:
Make sure that each valve is installed in its
original place, also referring to the embossed
mark as follows.
Intake: “G”
Exhaust: “L”
Install the valve springs with the larger pitch
a facing upwards.
bSmaller pitch
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3. Install:
Valve 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.

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ENGCYLINDER AND PISTON
Piston ring
1. Measure:
Ring 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:
Piston 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:
Ring 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)—

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ENG

CYLINDER AND PISTON
Piston pin
1. Inspect:

Piston pin
Blue discoloration/grooves
→

Replace, then inspect the lubrication
system.
2. Measure:

Piston pin outside diameter

Piston pin bore inside diameter
ASSEMBLY AND INSTALLATION
Piston
1. Install:

Piston rings
(onto the piston)
NOTE:


Be sure to install the piston rings so that the
manufacturer’s marks or numbers are
located on the upper side of the rings.

Lubricate the piston and piston rings liberally
with engine oil.
Measurement steps:

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)

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)

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ENG

CYLINDER AND PISTON
2. Position:

Top ring

2nd ring

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:

Piston
1


Piston pin
2


Piston pin clips
3

NOTE:


Apply engine oil onto the piston pin, piston
ring and piston.

Be sure that the arrow mark
a
on the piston
points to the exhaust side of the engine.

Before 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:

Piston

Piston rings

Cylinder
NOTE:

Apply a liberal coating of engine oil.
New

Cylinder
1. Install:

Dowel pins

Gasket

Cylinder
1

NOTE:

Install the cylinder with one hand while com-
pressing the piston rings with the other hand.
CAUTION:


Be careful not to damage the timing chain
damper during installation.

Pass the timing chain through the timing
chain cavity.
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