Excellent advice. Same idea. Ive heard to the paper all the way around the comm and tape it. Then take a pencil and stick it down in the brush holders (at the same identical spot in each holder) and make a mark. Then pull out the paper and measure between the marks, they should all be the exact same dimension from each other. May help if you label the holders like a clock, 2:00, 4:00 etc.
Helpful trick, I don't know how well know this is but works great. Even with neutral set right brush holders can be set at different angles so brushes are not on proper comm segment at the right time. So take a piece of adding machine paper and wrap it around the comm. Cut it off when it overlaps in a valley between segments. Now remove paper and fold in half then half again. Now wrap back around comm and tape ends together. Now you can set the leading edge of each brush to the lines made when you folded the paper and you will have a perfectly quartered comm.
