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:
Care
While the open design of a motorcycle
reveals the attractiveness of the technology,
it also makes it more vulnerable.
Rust and corrosion can develop
even if high-quality components are
used. A rusty exhaust pipe may go unnoticed
on a car, however, it detracts
from the overall appearanc ...
Troubleshooting charts
Starting problems or poor engine performance
Starting problems or poor engine performance
Engine overheating
WARNING
Do not remove the radiator cap when the engine and radiator are hot.
Scalding hot fluid and steam may be
blown out under pressure, which could cause serious injury. Be ...
Troubleshooting
Although Yamaha motorcycles receive
a thorough inspection before shipment
from the factory, trouble may occur during
operation. Any problem in the fuel,
compression, or ignition systems, for
example, can cause poor starting and
loss of power.
The following troubleshooting charts
repre ...