On your motor comm there are 3 segmets of copper with 3 slits in the comm. Make sure that there is not a large gap beteween the slit. When you cut the Comm you have to take a exacto knife and run it down the slit to clean it out and then take a ball point pen and run it up and down the slit so that it is not sticking up but rounded down so the brush does not catch on the segment.