Lionel SD60M derail on Atlas switches

I doubt we'll ever know what Lionel engineering specs the "correct" wheel back-to-back spacing. That being said, I think you've answered your own question when you say that the 1.070" or less spacing doesn't have derailment issues.

Try popping a leading wheel set out of one of your diesels and slowly decrease that back-to-back distance to 1.070", re-install, and see what happens. If you have a bench vise, decreasing the distance is a snap to do. Measure with an inside micrometer for accuracy.

JFC454 posted:

I just bought 3 of the new run Atlas O72 switches .  I have 4 of the Lionel SD60M from 2017.  When heading into the diverging leg of the switch, approaching the sharp point of the frog, the leading wheel set (non-geared) rides up the frog point and derails.  Every engine, every switch, both forward and reverse even at speed step 1.  No problem with 3 Atlas Dash8-CW or 6 Lionel engines produced before the SD60Ms.  Inside gauge measurement on leading wheels measures 1.100" for the SD60Ms, 1.070" or less on the engines that have no problem.  What gauge measurement are the wheels suppose to be?

Any suggestions would be appreciated.  Thanks.

I had same problem.  There was too much gap between the  guard rail and inner or outer.  I put styrene shims glued to the side of the guard rail.  It helped a lot.  I do have to file it for tweaking.  I had the problem on a few engines and did not want to adjust wheels on all of them.  Search more for this problem and you will find solutions.  They are not all that rare.