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:
General maintenance and lubrication chart
TIP
The air filter needs more frequent service if you are riding in
unusually wet or dusty areas.
Hydraulic brake service
Regularly check and, if necessary, correct the brake fluid level.
Every two years change the brake fluid.
Replace the brake hoses every four ye ...
Periodic maintenance and adjustment
Periodic inspection, adjustment, and lubrication
will keep your vehicle in the
safest and most efficient condition possible.
Safety is an obligation of the vehicle
owner/operator. The most important
points of vehicle inspection, adjustment,
and lubrication are explained on
the followin ...
Engine oil and oil filter element
The engine oil level should be checked
before each ride. In addition, the oil
must be changed and the oil filter element
replaced at the intervals specified
in the periodic maintenance and lubrication
chart.
To check the engine oil level
Place the vehicle on a level surface
and hol ...