Thanks for the info guys.  I will likely just look for another - perhaps the Plymouth MDT or the 44-ton switcher.

I have a Burlington Route MDT Plymouth Switcher that is about 20 years old.  I put it on the track and it would light but not move.  I pulled the body shell off to see what was going on.  When applying throttle the motor would jerk maybe 15 degrees and stop... with a little hum.  If I turned the motor with my finger it would turn a little by itself but then stop.  When I put the throttle up farther I saw sparks and eventually smoke from the front of the motor.  The problem does not seem to be in the gears as they seem to turn freely but for the motor.

What is the problem?  Do I need to order a new motor or can this be cleaned?

I really want a Bethlehem Steel body shell.  Any chance they will be available separately?  Or should I just buy a whole new engine?