Thanks all for the advice, I have a green one that 'chugs' at low speed, but rips when the voltage increases. Be aware: the can motor engines sometimes have a poor gear mesh between the motor worm gear and that brass worm wheel that it connects too. I have had to remove the motor bracket, drill out the holes in the frame that the screws go through, then reinstall the motor bracket and check the mesh. That grinding sound is probably the edges of the worm wheel get machined down. If you catch it quick and make the adjustment, you may not need a new worm wheel. You can still find that part, but it will become scarce quickly, as so many of the Contemporary standard gauge locos use that gear and have that problem. Once you do the mod, I think the loco will be good for a long time.
Jim
