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:
Overheating
Engine
1. Clogged coolant passages
Cylinder head and piston
Heavy carbon buildup
2. Engine oil
Incorrect oil level
Incorrect oil viscosity
Inferior oil quality
Cooling system
1. Coolant
Low coolant level
2. Radiator
Damaged or leaking radiator
Faulty radiator cap
...
Front wheel
To remove the front wheel
WARNING
To avoid injury, securely support the
vehicle so there is no danger of it
falling over.
Loosen the front wheel axle pinch
bolt, then the wheel axle and the
brake caliper bolts.
Front wheel axle pinch bolt
Lift the front wheel of ...
Assembling the main axle and drive axle
1. Install:
Toothed washer "1"
Circlip "2"
NOTE:
Be sure to install the circlip so that its sharp
edge "a" is facing away from the toothed washer
and gear.
Be sure the circlip ends "b" are positioned at
the axle spline groove "c".
2. Install:
2nd pinion gear "1"
NO ...