G Gauge Newbie Part 2

One of the locomotives in my "deal you can't refuse" initiation into G gauge is a Bachmann 4-6-0. It would not run and just shuddered and made a noise like a coffee grinder. I opened it up and found a motor smaller than that in some HO diesels driving through a plastic crown gear and spur gear reduction train. The gear on the motor was not meshing well with the crown gear due to wear. I added a shim washer behind the crown gear to hold it against the motor gear and it now runs, but still sounds like I'll soon get a pound of drip grind. It seems like it should really have a better motor, and a worm gear drive. Is anyone aware of an article on upgrading the drive train in these bargain locos? Gary Q