I recently purchased an Athearn RTR SD39 and it does not like the 18 radius of my layout at all. Is there anything that can be done to help it not derail? I know 18 radius is tight for 6 axles but I have a few ( athearn RTR sd60, walthers sd60, walthers GEVO, proto SD9 and a bachmann SD40-2) and all run just fine over every inch of the layout
I would not do that. My PAs look silly on my 24" radius curves.
There is nothing wrong with 18", or even 15" radius curves, but you need to select the correct equipment if you are going to do this.
-Kevin
Living the dream.
Check how freely the trucks swing. Take the shell off, watch the drive train as you move the trucks, from side to side.
Mike.
My You Tube
Sometimes there are small tweaks that can be done to allow tighter turns. This may hurt some details of the engine, though.
You need to look at how the engine handles curves, and particularly how it doesn't. Find out what interferes with the truck making tighter turns. It may be side stirrups, or even the openings in the frame itself. You need to look at removing the obstacles.
It takes an iron man to play with a toy iron horse.