1. The water in the motor causes short circuit and burns out the motor;
2. The commutator is short circuited and burnt out due to overload operation of motor.The phenomenon is that the commutator turns black (the motor cannot operate for more than one minute under overload).4、 The cause of abnormal noise of motor.
1. The concentricity of motor and rear axle is not up to standard;
2. Brush and commutator joint is not good, need to be adjusted; 3. If the bearing on the rotor inside the motor is damaged, replace it;