OK, I bought a new Tweetsie 4-6-0. Headlight, sound and smoke all work nicely.  My problem is that the new loco is derailing on my curves about 95% of the time.  I checked them with a level and they are level with no obstructions.  I knelt down as the locomotive was slowly coming and when it reached the curve it looked like the pilot truck wheels are floating or just lightly touching the rail. 
--The times it does not derail the locomotive wobbles as if it was top heavy.
--My old yellow/black 4-6-0 can handle these curves at full throttle and without any issues.
--I have been told that the wheels might be "out of gauge".  I have no idea what that means or how to fix it. Can someone please explain that to me and what I can do to remedy this situation.
--Does this occur with new locomotives?
--Is there a way to bring my pilot/truck wheels down so they are not floating around (like an extra washer or a longer screw)?  They are not guiding the engine around the curve and it is wanting to go straight instead of turn.

Gauge is the gap between the rails, in this case it is the distance between the wheels.  Measure the distance between the leading wheels that work and the wheels that don't.  If here is a difference adjust the misfits accordingly.  It may be necessary to take them out of the truck.  Gently twist them in or out to get the correct separation.  I think that the back to back spacing of the wheels should be 1.575 inches.  If I am wrong someone will give the correct value.

Chuck

Hey Steve,

Check out George Schreyer's website for Big Hauler issues... derailments is the first topic on the page!

http://www.girr.org/girr/tips/tips1/big_hauler_tips.html

Good luck!
Jay

Steve:

Sorry it took me a couple of days to get to your email.  I don't regularly check for messages here on the Bachmann site.  The only time I login is when need to make a comment or suggestion.

Chuck

The way the wheels are mounted on the axles is the issue.  In each wheel there is a plastic insert which mimics the metal wheel spokes, push the insert out from the back of the wheel, the insert can be removed (not completely, unless the rod post is loosened and the siderod removed.  Not necessary, yet).
With the insert loosened you can see a phillips screw at the center of the wheel into the axle, these can be loose, Tighten and move on to all of flanged drivers, front and rear.  If you have found even one of these loose you have probably found your problem.

Barry