Checking The Starter Motor - Yamaha YZ450FX 2019 Owner's Service Manual

EAM30106

CHECKING THE STARTER MOTOR

1. Check:
• Commutator
Dirt  Clean with 600 grit sandpaper.
2. Measure:
• Commutator diameter "a"
Out of specification  Replace the starter
motor.
Commutator diameter
80.6 mm (3.17 in)
3. Measure:
• Mica undercut "a"
Out of specification  Scrape the mica to the
proper measurement with a hacksaw blade
that has been grounded to fit the commutator.
Mica undercut (depth)
2.40 mm (0.09 in)
TIP
The mica of the commutator must be undercut to
ensure proper operation of the commutator.
4. Measure:
• Armature assembly resistances (commutator
and insulation)
Out of specification  Replace the starter
motor.
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a. Measure the armature assembly resistances
"1" with the digital circuit tester.
ELECTRIC STARTER
Digital circuit tester (CD732)
90890-03243
Model 88 Multimeter with tachom-
eter
YU-A1927
Armature coil resistance "1"
0.008–0.010 
Insulation resistance "2"
Above 1 M
b. If any resistance is out of specification, re-
place the starter motor.
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5. Measure:
• Brush length "a"
Out of specification  Replace the brush set.
Brush overall length limit
5.5 mm (0.22 in)
6. Measure:
• Brush spring force
Out of specification  Replace the brush set.
Brush spring force
4.80–7.20 N (489–734 gf, 17.28–
25.92 oz)
7. Check:
• Gear teeth
Damage/wear  Replace the starter motor.
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