Yamaha WR450F(R) Owner's Service Manual page 307

ELECTRIC STARTING SYSTEM
INSPECTION AND REPAIR
1. Check:
2. Measure:
3. Measure:
NOTE:
The mica must be undercut to ensure proper
operation of the commutator.
4. Measure:
Measure the armature assembly resis-
G
tances with the pocket tester.
If any resistance is out of specification,
G
replace the starter motor.
6 - 14
ELEC
Commutator
G
Dirt → Clean with 600 grit sandpaper.
Commutator diameter a
G
Out of specification → Replace the
starter motor.
Min. commutator diameter
16.6 mm (0.65 in)
Mica undercut a
G
Out of specification → Scrape the mica
to the proper measurement with a
hacksaw blade which
grounded to fit the commutator.
Mica undercut
1.5 mm (0.06 in)
Armature assembly resistances (com-
G
mutator and insulation)
Out of specification → Replace the
starter motor.
Pocket tester
YU-03112-C/90890-03112
Armature assembly
Commutator resistance 1
0.0117 ~ 0.0143 Ω at 20 ˚C
(68 ˚F)
Insulation resistance 2
Above 1 MΩ at 20˚C (68 ˚F)
– +
has been