�Hoping somebody can give me some guidance and advice.  I have two N scale Bachmann U36B's that are from around 1974, made in aging Kong.  I have taken them apart, cleaned them and lubricated, but still all they do is smoke and barely move. My question is if I want to keep the shell and use it on a different U36B, is there a newer model that Bachmann improved upon their gearing? Will the shell fit on, say an Athern?