Motor problem !

[Andy]

I got a Tinity D3 11 -turn and GM 17-turn motor. Both have have the same problem :
I have cut the com and it looks shiny as it should all around only where the com is split it is still black. I don´t want to cut the com any more because I have had other motors that chipped after I had cut them down too much (at least that´s what I think ) . This balck spot makes the brushes arch which I am afraid will ruin the motor even faster.
What shall I do ?

[I R Racer]

I assume you mean the 3 grooves in the comm when you say, "where the comm is split". If you are, then I believe that it is always black in the grooves, all the comms I have ever seen or cut myself have black grooves. Usually I run the blade of an exacto-knife down the grooves to remove any debris.

[Andy]

Yes, I mean the three grooves in the comm.
I know that they are black and are supposed to be. My problem though is that the comm itself is black just next to these grooves . It actually looks as if the grooves are slightly broader in the middle of the comm compared to the ends of the comm - just as if the comm is already "ruined" there - as if there is nothing to remove. Any suggestions ??