Be careful if you decide to do this to your motors because you could do more harm than good. The commutator should end up perfectly concentric with the motor shafts, and perfectly smooth and shiny. I examined the connection between the leads and the brush housings. I securely soldered all the leads. While I had my soldering iron out, I decided to install capacitors across the leads.
Capacitors quiet the radio frequency noise that the motors generate.
This noise will interfere with your radio. I once built a robot that had a radio range of about 15 feet. Use 0.1 uF ceramic disk capacitors. Solder one across the leads as close to the brushes as possible. The idea is to mount a pulley or sprocket onto the shaft with a set screw tightened onto the flat.