Cannot keep the front truck on the rails.

Take the truck off and push it through your switches by hand, observing how it traverses the switch. Are the flanges too much for those particular switches? Does it seem to want to jump up and over any rail? Does it bounce through the rails? …..use a screwdriver or a stick, and push the truck through the switch from a point that doesn’t exert any downward pressure like your fingers would tend to do. Sadly, I hate those crappy pilot trucks and generally toss them in the trash when I’m doing an upgrade ….they’re about as clunky as clunky gets …..

Pat

So I have recently acquired two Williams brass locos, each seems to have it's own similar issue to what you describe, Atlas switches here, when taking the diversion direction my N&W 611 4-8-4 will seemingly hit something in the switch or rail and pop out, or most of the time I hear it lifting on top of the rail then it will fall back down onto the rail.

I also have a NYC 6010 Niagara 4-8-4 I just got and I noticed as it takes left hand O72 curves the front truck swings and will snag on a low hanging compressor. I found someone else mention this on the forum and they fixed it by file it down a bit.

Is the spring putting the right amount of pressure on the truck? You might want to try stretching it a bit (and then cutting it a bit shorter to compensate) and see if that puts more pressure on the pilot truck. If you are scared to do that, take the spring to a hardware store to see if they had a similar one and then try that.

@Quay Beck , depending upon the set up your engine has, perhaps the post by D500 in this thread is helpful:  2-8-0 derailing.

There is a solution for this on Atlas switches that may apply. I'll provide the details after the moderators move to the correct forum.

I had a problem with the front truck lifting on reverse curves at siding switches, on a Sunset/3rd Rail brass 4-8-4.  I loosened the screw which attached the truck, and the problem went away.

Brass engines are built by hand, and some periodic adjusting is not uncommon.

I had the same problem with 2 wheel front truck and other engines in general because of a flaw in the dimensions of some early Atlas switches. The problem and one solution is discussed in a figure I can't seem to find at the moment (maybe it's at home). Basically, my solution was to add height where the wheel enters the guide rail opposite the frog in a way that forces the wheel/truck to turn just a little sooner. Otherwise it jumps the wedge part of the frog and derails OR it climbs and falls back into the slot and you get an ugly "clunk" sound. I added the height with a short length of stainless steel strip that you'll find inside most car wiper blades. Works really well. I can send a photo after I get back home.

A lot of times this is fixed with shimming the track or switch till it works.  You don’t want the engine’s nose up going into a switch.  Then it jumps the rails.