Yamaha TT-R90(V) Owner's Service Manual page 366

ELECTRIC STARTING SYSTEM (TT-R90E)
INSPECTION AND REPAIR
1. Inspect:
• Commutator
Dirt → Clean it with #600 grit sandpaper.
2. Measure:
• Commutator diameter a
Commutator wear limit:
16.6 mm (0.65 in)
Out of specification → Replace the
starter motor.
3. Measure:
• Mica undercut a
Mica undercut:
1.35 mm (0.05 in)
Out of specification → Scrape the mica to
the proper value (a hacksaw blade can
be ground to fit).
NOTE:
The mica insulation of the commutator must be
undercut to ensure proper operation of com-
mutator.
4. Measure:
• Armature assembly resistance (commu-
tator and insulation)
Out of specification → Replace the
starter motor.
Measurement steps:
• Measure the armature assembly resis-
tances with the pocket tester.
Pocket tester:
YU-3112-C/90890-03112
Armature coil:
Commutator resistance 1
0.018 ~ 0.022 Ω at 20 °C (68 °F)
Insulation resistance 2
Above 1 MΩ at 20 °C (68 °F)
• If any resistance is out of specification,
replace the starter motor.
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