GEC's Layout Progress

[Green_Elite_Cab]

I think i've hit a different sort of problem with my Athearn Genesis GP15-1. Does anyone know what the wheels are actually made of? I clean up the wheels with a bright boy, but when i did, i notices a discolored area along where the rails would contact the wheels. Instead of the usual nickel silver look, it had a more coppery color, and it almost seemed pitted. The locomotive runs fine now, but i have never seen anything like that on my Atlas, P2k, Bachmann, or other Athearn locomotives.

Perhaps this is the source of the weird problems with the GP15-1s i keep hearing about?