I mentioned in another thread that I did a motor swap in Delaware. This was due to a hall sensor failure, but as things turned out, I'd ordered a replacement motor that was supposed to arrive after my trip, but it arrived the day before the trip, so I took it with me! The new motor worked fine, but after a high speed ride alongside gas bikes, I noticed an odd noise that sounded like gears slipping. I pulled the motor apart and found the nylon gears were fine, so I switched the clutch out, and still had the noise.
The ring gear tested fine as well, then I saw it: The replacement motor was missing the internal lacing! That's the string-like cord used to secure the coils and other bits. Without it, the wires are subject to vibration and movement, and this leads to metal fatigue and failure. This is common is cheap throwaway motors, but motors built to last usually have the internal lacing, I was surprised Bafang went in this direction. The only reason to do so is because it's cheaper and saves time and materials. The motor itself works fine, and although the motor on the right is better made, it's out of commission due to the sensor failure. So I went to the hardware store, got some appropriate string, laced up the critical spots, glued the knots, and tested it. The noise is gone and I can use full power again, so we shall see how it holds up!