Excessive heat can cause a commutator to become what, or out of round?

• A. Circular
• B. Oval
• C. Eccentric
• D. Warped

Answer: (C)

Excessive heat causes a commutator to distort because the metal expands unevenly. The commutator is a cylindrical surface that must turn true around the shaft. When it overheats, it can expand more on one side or at different rates, so the surface no longer shares the same center as the shaft. That misalignment is called eccentricity—the axis of the commutator is no longer concentric with the shaft, so as it spins the brushes see varying gaps and the surface appears out of round. This leads to uneven brush contact, increased sparking, and accelerated wear.

The other terms describe shapes the part might take, but they don’t capture the typical problem in this case. Circular would be the desired shape; oval isn’t the standard diagnostic term for this distortion; warped implies bending in a way that isn’t the usual result of uniform heating for a cylindrical surface. Eccentricity is the precise way to describe a cylindrical surface whose centerline is off from the shaft.