Under heavy operating temperatures, how does commutator trueness change?

• A. It remains within .002 inches
• B. Reduces to .001 inches
• C. It can distort and exceed .002 inches
• D. It becomes perfect

Answer: (C)

When a commutator heats up during heavy operation, its trueness can worsen because metals expand with heat at different rates and heat distribution is rarely perfectly even. That uneven expansion and the internal stresses can cause the commutator surface to warp or run out, so the runout can exceed the specified tolerance of about 0.002 inches. So the best answer is that it can distort and exceed 0.002 inches.

Under those conditions, the other statements don’t fit because heat does not make the surface more precise or bring it to a smaller tolerance. It isn’t guaranteed to stay within 0.002 inches, and it certainly won’t become perfect just from operating at high temperature. When excess trueness deviation occurs, the usual remedy is re-truing or skimming the commutator to restore a true, concentric surface.