Starting contactors are either manually or magnetically operated and are designed to be operated for only short periods of time. Starter motor troubles can be traced for the most part to the commutator, brushes, or insulation. If motors are to function properly, they must be kept clean and dry. Dirt and moisture make good commutation impossible. Dirty and fouled starter motors may be caused by failure to replace the cover band, by water leakage, or by excess lubrication.
Most starter motors have a cover to protect the commutator and windings.
If you neglect to replace the cover or remove it as an aid to ventilation and cooling, dirt and water are sure to damage the equipment. Although lubrication of bearings is essential for proper operation, excessive lubrication may lead to trouble in a starter motor. Excess lubricant in the shaft bearings may leak or be forced past the seal and foul the insulating material, commutator, and brushes. The lubricant prevents a good electrical contact between the brushes and the commutator, causing the commutator to spark and heat and the brushes to burn. Burned brushes are another possible source of trouble if the starter motor is inoperative.