LIONEL LEGACY K4 #6-11319 DERAILS

Michael,

Your comment "I suspect that although it is rated for 036 curves the loco's drivers have a footprint that is just a little to long for tighter curves ..." seems to be at odds with your first comment "... never had any problems running it through 036 Fastrack curves or turnouts until recently". 

Even though you stated you could find no obvious problems, it sounds like to me that something has changed.  I had a little "accident" with a K-Line steamer once and it never ran quite right after that.  Or maybe the track where the engine is derailing is uneven now and it wasn't before.  Traction tire still good?  It could be several reasons, but for this case I'd start looking for what might have changed.

Is it possible the rear set of drivers is out of gauge, ie wider than they are supposed to be?  If they are coming loose that could be a cause potentially.

Front or rear truck issues can cause derailments, and not just the trucks themselves. Are both - especially the rear - trucks' wheel sets still solidly mounted (bearings can slip out of the truck sides)? Are they still in gauge? Are the pivot and suspension in place properly? Something caught up in the truck area?

I had an MTH 2-8-2 with a front truck that would derail over any switch - I looked and realized that they had not installed a sleeve on the mounting post and this allowed extra slop in the truck pivot; a piece of brass tubing fixed it. Not the drive wheels, but it wasn't obvious at first, either. 

Could you accidentally have the tender pin in the forward hole in the drawbar?  I can run mine this way only because I have 072 minimums.  I seriously doubt it would negotiate 036 curves in that position. 

Bruce