lionel legacy 0-8-0 steam engine derails on gargraves 0-42 switches

I know it sounds insensitive to your problem but: don't do that and it won't happen. I don't think you can fix it well so that it both will not happen with this loco and also not plague the occasional other loco in the future.  Maybe someone else has a solution that will always work but my experience was . . . 

When I redid my layout with Atlas track, based on their excellent reputation, I tried two Gargraves switches and had similar problems with a couple of different brands of pilotless locos (Lionel 0-4-0, MTH 0-6-0).  Most of my locos -- all that had front pilots, seemed to do fine, they would go through them with no problems, but both 0-4-0s and the MTH 0-6-0 would not, and a Lionel 0-8-0 would sometimes not: maybe once if four times de-rail there, too.  I fussed with tried to diagnose the problem and eventually went to the trouble of using Fastrack switches and making transitions to and from the Atlas around them (which was indeed a pain).  

On many of the older Gargraves switches the frog sits above the rest of the rails. You can either take a dremel and cut the space between the rails for the flange deeper or what I do is pop out the frog and remove material from the under side so it sits lower. Check the fit with a truck to make sure the flange does not touch the frog.

Pete

Thanks for your all of your suggestions.

After fiddling around with the frog height

and other stuff, I got it working reliably.