They will wear into full contact very quickly, particularly in the case of the carbon brushes in the generator. The sintered copper starter brushes wear much more slowly, but they're already radiused to a pretty close fit to the commutator.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!