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.
Electric starter
...
Assembling the starter motor
1. Install:
Starter motor front cover/brush holder set "1"
Starter motor yoke "2"
NOTE:
Align the marks "a" on the starter motor yoke and
starter motor front cover/brush holder set.
...
Other materials:
Removing the rear brake caliper
NOTE:
Before disassembling the brake caliper, drain
the brake fluid from the entire brake system.
1. Remove:
Union bolt "1"
Copper washers "2"
Brake hose "3"
NOTE:
Put the end of the brake hose into a container
and pump out the brake fluid carefully. ...
Checking the fuel line
1. Remove:
Left side panel
Refer to "GENERAL CHASSIS" on page 4-1.
2. Lift the fuel tank. (Do not disconnect the fuel
hose, drain hose
3. Check:
Fuel hose "1"
Cracks/damage → Replace.
Loose connection Connect properly.
4. Install:
Fuel tank
Refer to "FUEL TANK" on pa ...
Checking the camshaft
1. Check:
Camshaft lobes
Blue discoloration/pitting/scratches
Replace
the camshaft.
2. Measure:
Camshaft lobe dimensions "a" and "b"
Out of specification Replace
the camshaft.
3. Check:
Camshaft oil passage
Obstruction Blow out with
compressed air. ...