Recently I purchased a Gem brass Pennsy S-2 steam turbine. It’s so old the box disintegrated but he loco itself is a beauty and runs well if a little noisy. Unfortunately the six wheel leading and trailing trucks will not track reliably. They keep wanting to derail at any opportunity. I’ve tried adding weight ( 1/4 oz stick ons ) but the problem persists. I’m reluctant to install stronger truck springs because that robs the drivers of traction. If anyone has solved this problem or has a suggestion I’d like to hear about it.
It sounds to me like weight or springing could help, but perhaps it is the condition of the locomotive after all? I’m thinking about the way the trucks are mounted and how easily they ‘float’ under the frame as the drivers shove and pull them severally. I would assume that, as they are brass, they ought to be plenty heavy already. I would be looking for a problem with the way they pivot or swing laterally. Perhaps their mounting screws are too tight and need to be backed out a half-turn or more. Or they need lubrication. Or they have been swapped/reversed and just don’t ride well as a result.
I know this might not be applicable, especially if your other engines work just fine, although mine did as well when I got my first problem steamer, the BLI UP-2-10-2 Brass Hybrid. It’s tender kept derailing on curves. I finally decided to experiment by softening my ballast and prying up the outer rail about half a mm more along an arc where they derailment seemed to take place, plus a bit toward the rear since I needed a transition. That worked. It may be that you need more superelevation for a short distance.