You have to evaluate each switch individually. Gather some spare trucks, representing every era and manufacturer for your equipment, and--using your hand--push them through the turnout at the most unlikely, cockeyed angle you can, and see where the derailment occurs. The most common problems on our layout have been:
Combination of loose spring tension and blunt points cause the train to "pick the points" and go onto the wrong track.
Too-short guardrails allow rolling stock with wobbly wheelsets to enter the wrong "side" of the frog when going "facing point" thru the switch. Guardrails can be replaced with longer ones--Ross will sell you some sharp-looking aluminum ones that work great and can be installed with epoxy.
On some turnouts which do not have one-piece frogs (i.e., the rails from points continue in to the frog area, and a small plastic "floor" is provided for the tinplate flange to run on) the flange can become trapped in the small gap between the rail and the "floor" of the frog. This gap can be filled with epoxy.
A short between the 3rd rail "plate" between the rails of a Gargraves switch and the flange of a passing car. Sometime this plate is installed rather close to the rail, and a wheelset that is not quite 'true' can brush against it. A little piece of electrical tape on the side of the plate fixes this. Also make sure the points are electrically isolated from the rest of the turnout--no filings, etc. in the gap between the trailing end of the point and the part of the rail that enters the frog.
And don't automatically acquit your motive power and rolling stock. For example, we found that our postwar aluminum passenger cars had wheels set too far apart. They derailed constantly until we put spacers (horseshoe clips) at the ends of the axles to hold the wheels in gauge. A second example, we have a Mike (Lionel 1993) that for some reason had a large square hole in the "drawbar" for the leading truck (where it is attached to the frame with a bolt). We filled the hole with a big washer, and the engine stopped picking points. There are LOTS of things that can go wrong.
When I was an engineer with the Southern Pacific and then the Union Pacific Railroad, we always described the movement following the direction of the way the switch was lined as a "Facing point movement". You pass over the points first and then the frog. When backing or moving forward through a switch so as to get other side of the switch thus allowing it to be lined as desired, we referred to that as a "Trailing point movement" or "Trailing through a switch". You pass over the frog first then the points. Hopefully it is lined for your movement otherwise what results is a Run-through switch in which case you might end up with a few unintended days off.
This may help you in the future when trying to describe the problems regarding derailments of trains moving through turnouts. Sorry to say I can't offer a solution to your engine's problem.
For simplicity I call the Turnout/WYE with the single track the "front", and the double track portion the back.
On a couple of my K-Line Mikes the tension on the leading trucks was a bit light and at times it would climb the rails when entering a turnout set to the curve or a wye.
When entering the back of a turnout/wye with the points in a closed position the tension on the centering spring can cause problems for leading trucks on steamers and on some of the lighter rolling stock (Weaver, 6464, etc).
Remember the Veterans. Past, present and future.
www.sd3r.org
Proud New Member Of The NRA
"Frog"? You must mean "points".
Bob Nelson
From which direction is the loco approaching the turnout ?
Is the turnout open or closed ?
If it is the leading truck that is derailing you mite check to see if there is sufficient down force to keep the truck firmly on the rails.
Also if they are Atlas turnouts you mite be able to adjust the spring tension holding the points in the closed position, if excessive it could also cause the leading truck to climb up-n-over the rails instead of passing thru a "closed" turnout.
Our community is FREE to join. To participate you must either login or register for an account.
Get the Classic Toy Trains newsletter delivered to your inbox twice a month