
Here's what the comm-plate looks like for the AFX mini-can. Brushes are your basic copper carbon unit, so they break in relatively easy. They are not pre-shaped to conform to the commutator, so a good break in is critical for optimum performance and longevity. The flat faced brush is nowhere near ready to transfer full current properly to the commutator under a load. Hence the conventional wisdom regarding break-in for the Mega G+


Look at all that wire! The Mega Gee+ is a fairly docile 17 ohm wind with benevolent magnets; all designed so lil Johnny wont burn his "finners", yet providing a nice long, very useable, mid range band, as lil motors go. The side view reveals that the pole bundles at shaft end of the armature are tamped flat at the factory, presumably so they dont rub the inside of the can. Notably in comparison, the comm ends sport a nice parabolic loop. I've only had two apart, but it is a bit odd.
If the chassis is dead new out of the package, start by finger rolling the chassis back and forth to scrape any oxidation off the commutator, so you get a good "first-start" when you apply voltage. I try to never cold start a motor/chassis that has been sitting. Pop the rear axle out carefully so there will be no motor load. Oil the shaft end LIGHTLY with a needle oiler. The comm plate end has a dust shutter, so it cant be lubed without modifying the shutter. Mount or stabilize the chassis in a clamp, so that you can hear only the motor; and not any of the weird harmonics or clattering vibrations that occur, when you run a chassis loose on the bench.
You'll need to regulate power, so you can start out at lower voltage. I use an ancient wheel controller with leads and small gator clips.
The motor should be run at 0 to 1/4 throttle. Just enough so that it lopes along smoothly. I usually occupy myself with other tasks at the bench, but keep and ear tuned to the motor and poke it with a finger to get a read on how much heat is being made. For other high ohm zoopy motors with black hole magnets, that like to heat up a bit, there's absolutely no reason you can beg off and continue when things cool down, assuming you've checked for any latent friction issues.
As the brushes begin to seat, you'll hear the tune change as the motor picks up RPM, and or smooths out. When things clean up you'll reach a plateau, where there is no change. Ease the throttle up to half, and let her chew on that a while. Same deal, keep your ears alert and poke it for heat once in a while. Repeat at 3/4 throttle as well.
From 3/4 throttle on up, I like to put the axle back in; so the motor has a load. Creep up on full throttle carefully. Keep in mind that an H0 chassis can fling it's tires at high RPM and shoot them across the room. Excessive pee winding of the motor/chassis serves no useful purpose. It's best to finish up on the track, maintaining a medium steady lap speed, and then bringing max throttle in gradually for the straights and sweepers.
Some guys like to provide or adhere to a specific time/hrs on the break-in block and walk away. I'm more of a believer in "ears on"; because not all brushes are created equally, nor are all commutators.
Good luck!