There may be several reasons for damage to the starter motor, including:

1. The starting time is too long, and the starter is not used according to the prescribed time (about 5-10 seconds). The starter is continuously started for a long time without identifying the cause.

2. When the electric brush wears down to half of its original length, it should be replaced. When maintaining the starter motor, it is necessary to regularly check the height and contact of the electric brush, and promptly eliminate any problems found, otherwise it may cause damage to the starter motor.

3. Poor contact of electromagnetic switch contacts, damage to one-way teeth and flywheel teeth. Poor iron tapping and other issues can cause starter failure.

4. Short circuit of the stator winding of the starting motor, damage to the commutator or short circuit caused by brush dust, local short circuit of the armature, poor contact caused by severe brush wear, severe wear of the motor bearings or uneven assembly axis, rotor drag shell, gear or pulley rupture, etc., all of which can cause the motor to fail to start.

Common symptoms of damaged starter motors include:

1. No rotation or slow rotation during startup.

2. There is a strange noise when starting.

3. The motor heats up during startup.

4. Excessive current during startup.

5. Failed to start.