Typically what happens is a racer forgets to put oil in their mag drive and you now the rest of the story, burnt bearings and gears but good news if you carry some spare parts in the trailer you can install some new parts and be back out on the track in a flash.
Hi-speed precision sealed ball bearing that goes in the top of the mag drive to help support the bronze gear. Bearing is a #6804RS, O.D. is 1.260", I.D. is .790" and thickness is .275"