Since our track looked at the cans to make sure the tabs hadn't been touched, you'd have to be REALLY good to not leave any marks to show otherwise. They looked to make sure you had no bearings as well. Trinity had brushed that could advance the timing 6 degrees. Aside from that if you are referring to using pliers to grab the commutator and slightly twist it to change the timing, isn't that called cheating? You could always try to zap the magnets too. The whole point of rules is to even the playing field. It's usually not the cheaters who win anyways but it is almost always the cheaters who complain the most about the rules.