Yamaha YZF-R125 Service Manual: 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.

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.

NOTE:

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.

a. Measure the armature assembly resistances with the pocket tester.

b. If any resistance is out of specification, replace the starter motor.

5. Measure:

• Brush length "a" Out of specification Replace
  the starter motor front cover/brush holder set.

6. Measure:

• Brush spring force Out of specification Replace
  the brush springs as a set.

7. Check:

Gear teeth Damage/wear  Replace the gear.

8. Check:

• Bearing
• Oil seal
• Damage/wear Replace the
  starter motor front cover/brush holder set.