I stoned the commentators on motors for years , with hit and miss results. yesterday I stoned one on a RD5200 Crown. The way I do it is to jack up the truck , pull one set of the brushes out , start motor running and stone the commentator.
Then all of a sudden it stopped and I saw a red glow in the motor just past the brush holder. I shut it off real quick , but now when I start it up it says "Please stand by" for about 20 seconds and the codes out to a 329 and 321.
Following the book I checked the modules 2 and 3 and they checked good.
I blew the motor out real good to, still no start.