length YAMAHA TTR90 2003 User Guide

4 - 18
ENGVALVES AND VALVE SPRINGS
Valve spring
1. Measure:
Valve spring free length a
Out of specification → Replace.
2. Measure:
Spring tilt a
Out of specification → Replace.
Free length (valve spring):
Intake:
32.45 mm (1.28 in)
: 26.9 mm (1.06 in)
Exhaust:
32.45 mm (1.28 in)
: 26.9 mm (1.06 in)
Spring tilt limit:
Intake:
2.5˚/1.4 mm (0.06 in)
Exhaust:
2.5˚/1.4 mm (0.06 in)
Valve seat
1. Measure:
Valve seat width a
Out of specification → Reface the valve
seat.
Valve seat width:
Intake:
0.9 ~ 1.1 mm (0.0354 ~ 0.0433 in)
: 1.6 mm (0.0630 in)
Exhaust:
0.9 ~ 1.1 mm (0.0354 ~ 0.0433 in)
: 1.6 mm (0.0630 in)
Measurement steps:
Apply Mechanic’s blueing dye (Dykem) b
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. Where the
valve seat and valve face made contact,
blueing will have been removed.
If the valve seat is too wide, too narrow, or
the seat is not centered, the valve seat
must be refaced.

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ENGCLUTCH
EC484600
Clutch plate
1. Measure:
Clutch plate warpage
Out of specification → Replace clutch
plate as a set.
Use a surface plate 1 and thickness
gauge 2.
EC484400
Clutch spring
1. Measure:
Clutch spring free length a
Out of specification → Replace springs
as a set.
Push rod
1. Measure:
Push rod #2 bend
Out of specification → Replace.
Warp limit:
0.2 mm (0.008 in)
Clutch spring free length
Standard Limit
26.2 mm
(1.03 in)24.2 mm
(0.95 in)
Bending limit:
0.5 mm (0.02 in)
Primary clutch
1. Measure:
Primary clutch housing inside diameter
Out of specification → Replace.
Primary clutch housing inside
diameter:
105 mm (4.13 in)
: 106 mm (4.17 in)
2. Measure:
Clutch shoe groove depth a
Out of specification → Replace.
Clutch shoe groove depth:
1.0 ~ 1.3 mm (0.039 ~ 0.051 in)
: 0.1 mm (0.004 in)

6 - 13
–+ELEC
5. Measure:
Brush length a
Out of specification → Replace.
Brush length wear limit:
3.5 mm (0.14 in)
6. Measure:
Brush spring force
Fatigue/out of specification → Replace
as a set.
Brush spring force:
3.92 ~ 5.88 N
(400 ~ 600 g, 14.1 ~ 21.2 oz)
ASSEMBLY
1. Install:
Brush holder
2. Install:
Armature coil 1
3. Install:
Ring 1
Stator assembly 2
Front bracket 3
NOTE:
Apply molybdenum grease lightly on to the
bearings of the starter motor.
Align the match mark on the yoke with the
match mark on the bracket.
ELECTRIC STARTING SYSTEM