When motors are manufactured, the comms are just kinda "shoved" into place, and are not completely round. That makes the brushes bounce, and the hotter the motor, the more they bounce. I think you really need to have the comms cut, at least to just know that they are not the problem. I know you don't have convenient access to a lathe or shop, but I will offer you this: If you want, you can ship me your armatures, and I will cut them for you, no charge. I have 14 years' experience in this hobby, and know very well what I am doing, so I can promise you that I will care for your parts very well. Let me know, you can PM or email me.


Matt