Locomotive Derailing

[Inukshuk]

I have a problem and can not think of a solution.  I have an Inter Mountain FP7A unit that continually derails at one of my turnouts.  None of my other locomotives derail there, and in fact the FP7B does not derail there.  Any ideas?

[MichaelWinicki]

Check the wheel gauge.

A good percentage of my loco issues have involved wheelsets that are usually too narrow.

[davefoxx]

Check the gauge of the wheel sets on the FP7.  It doesn’t take much out of gauge for a point to be picked.  Also, although unlikely since it doesn’t derail elsewhere, is to check for anything hanging low on the locomotive and that the trucks swing freely.

Hope this helps,
DFF

[hegstad1]

low hanging coupler trip pins can be a problem.

[nickelplate759]

All the posts here suggest (as would I) that the culprit is likely something on the locomotive that is out of spec.

That said, it's worth checking your track carefully as well.   I've had a few cases where the place that an out-of-spec locomotive derailed was also out-of-spec (kinked track, narrow gauge, etc.).

[Bendtracker1]

I had one IMRC F unit that would constantly catch and derail in several locations.
After careful inspection I found that one side of the truck frame was a touch lower and it was just enough to catch.
Was able to snap it back into place easily, cured the issues.
Might be worth a look?

[nkalanaga]

20 years ago, when laying the ME turnouts on my layout, the track worked fine - until I tried to run Kato Fs.  Almost invariably, the third of 4 units would derail, always at facing-point turnouts, always taking the curved side.  By itself, it ran fine.  If I turned the set around, the new 3rd unit, which had been the 2nd, would derail.  The one that derailed before worked fine.

I tore those locos apart looking for the problem.  Couldn't find a thing.  I tried other sets, as my BN has a LOT of Fs.  The 3rd of 4 units would derail, regardless of the unit. 

It finally turned out to be the turnouts.  The frogs were higher than the points, and the Kato Fs were designed so that the trucks could rock sideways.  When the front truck was on the frog, that side was higher than the stock rail.  That would lift the same side of the rear truck, just as it reached the points, and the flanges could lift over the point, derailing.  It didn't derail taking the straight route, because the trucks weren't turned.  Single units didn't derail, because the stresses were different.  Other models didn't derail because they either had more play in the trucks, or were run as single units, or had body-mounted couplers.

The Fs still had truck-mounted dummy couplers on the rear of the As and both ends of the Bs, and the pulling forces of the units in front and behind were affecting the truck rotation.  Also, I'd had the flanges turned down on my Fs, so it was easier for them to lift over the rail.

Yes, I've also had the "out of place truck frame" and "out of gauge wheels", but I wouldn't rule out a track problem completely.  A lot of shimming later, the track works fine, and the Fs run as well as any other units.  In fact, they became my test units for any new track!

[Inukshuk]

Thanks for the options.  I raised one side of the turnout so that it's camber went with the turn.  Seems to work, but I will check out all of the suggestions.

[Inukshuk]

Update.  Finally have been able to get the Loco to run.  It turned out to be a series of issues.  The coupler pins hyng to low.  The track work around the turnout needed to be improved and finally the wheel sets while within spec were on the outside limit, causing the wheels to push against the rails accentuating the poor track work.

[nkalanaga]

Yes, I've had the coupler pin problem as well, on both cars and locos.  Very puzzling derailments, as they only derail at turnouts and crossings, and sometimes only in one direction.  In a few cases the pins were right at the limit, and worked while pulling, but not pushing, or vice-versa.  Those are even harder to find!

Glad you got it fixed.  Now you shouldn't ever have problems with that turnout again, and if you do, it will almost certainly be the loco/car.