Greetings! I had hoped that my first post would involve showing off my layout progress, but unfortunately I'm here to ask yet another question about derailments (my apologies). I've been searching for a good while now, but I can't seem to determine what my issue is. I've got your standard N guage manual Peco insulfrog medium length turnouts (2 left, 2 right) that are causing one of my locos to spectaculaly derail. Each time it attempts to pass straight through the turnout (ie, not turning left/right off the mainline) the loco will flop onto its side, roll down the embankment and fall a few feet to the floor. The track is all brand new, the approach to the turnout is straight and only one loco has the problem. I have 3x Minitrix 2-6-0 steamers that have no problems, but I have recently aquired a 2nd hand LifeLife GP18 that can't get through. At a very very slow speed it makes it through and pushing it through by hand, I cannot feel any resistance or anything catching. At operating speed, the train stops and then flops onto its side. I've run it through 1000 times and I cannot visually see what is happening. There doesn't seem to be a pattern - sometimes it will fall with the front trucks over the frog, sometimes the rear. Looking at the wheels on the loco, the only thing I can think of is that the flange on the wheels is worn down and it is rolling sideways over the edge of the frog - can/does this happen? The minitrix steamers have a much larger wheel flange, but I expect that is more to do with the older design. Since I don't have any other locos the same age, I've got nothing to compare them too. That said, they are not a lot different to my Fleischmann cars. Can anyone suggest what might be unique to this loco that would be causing the problem? I've spent several nights watching it trying to see what happens, but since it only happens at speed, it's almost impossible to catch it as it happens. Once again, I'm sorry for asking a question that has no doubt been answered 1,000 times. Cheers, Scott.