What is typically required for maintaining large universal motors after extended use?

In large universal motors, especially after extended use, one of the critical maintenance tasks involves the replacement of carbon brushes. These brushes make contact with the commutator to conduct electrical current, allowing the motor to operate. Over time, due to the friction and wear as the brushes slide along the commutator, they can become worn down or damaged, leading to decreased performance, increased sparking, and potential motor failure.

Regular replacement of the carbon brushes ensures that the electric contact remains reliable and efficient, which is essential for optimal motor performance. This maintenance task is necessary to prevent excessive wear on the commutator itself, which can lead to more significant repairs or even a complete motor failure if neglected.

While other maintenance tasks may be relevant in specific situations—like oil lubrication for bearings, commutator cleaning to clear debris and ensure smooth operation, or field replacement under certain circumstances—the routine and most crucial task specifically tied to the continued operation of a universal motor focuses on the condition of the carbon brushes. Therefore, the answer highlights an essential aspect of motor maintenance that ensures longevity and functionality.