Yamaha WR250FR Owner's Service Manual page 309

ELECTRIC STARTING SYSTEM
INSPECTION AND REPAIR
1. Check:
• Commutator
2. Measure:
• Commutator diameter a
3. Measure:
• Mica undercut a
NOTE:
The mica must be undercut to ensure proper
operation of the commutator.
4. Measure:
• Armature assembly resistances (commu-
• Measure the armature assembly resis-
tances with the pocket tester.
• If any resistance is out of specification,
replace the starter motor.
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ELEC
Dirt → Clean with 600 grit sandpaper.
Out of specification → Replace the
starter motor.
Min. commutator diameter:
16.6 mm (0.65 in)
Out of specification → Scrape the mica to
the proper measurement with a hacksaw
blade which has been grounded to fit the
commutator.
Mica undercut:
1.5 mm (0.06 in)
tator and insulation)
Out of specification → Replace the
starter motor.
Pocket tester:
YU-3112-C/90890-03112
Armature assembly:
Commutator resistance 1:
0.0189 ~ 0.0231 Ω at 20 °C
(68 °F)
Insulation resistance 2:
Above 1 MΩ at 20 °C (68 °F)
– +