(This may look like a repair question, but I'm actually interested in how the simplest kind of motor failed)
This is the stator of a permanent-magnet single-phase motor from a washing machine drain pump:
There's two coils in series with a thermal interrupter, and a permanent-magnet rotor goes in the gap. That's all.
The rotor spins with force (I can't stop it with my fingers) but irregularly, especially in the first few seconds after applying power:
Conventional wisdom says the windings are shorted, so I measured R≈12Ω, ~6Ω each half (it's rated 85W@120V; I don't know of a rule of thumb to estimate the number of turns). In case both halves had similar partial shorts, I unwound one down to the bobbin and didn't find stuck turns or visibly bare copper. The rotor turns smoothly, snapping magnetically every 180°. Shorting the thermal interrupter doesn't change anything.
So, how else can this simple device fail to turn evenly?