I have several MTH Railking engines: GS-4, Hudson, Challenger, Big Boy and GG-1.
All ran great on my over head loops. That was until I installed cross over switrches.
The engines would phyically stall over the switches. It took some time and a lot of picking and testing.
I found out ALL of the screws that hold the wiper pads are a tad to long. They catch the rail head of the cross over rails.
They are as tight as I dare make them.