I am having an issue with the only two premier locomotives I have when running over a Lionel operating track.  The two MTH product numbers are: 20-21070-1 (LV RS-11) and 20-21108-1 (Reading GP-7).

As either locomotive crosses the center magnet of the operating track the wheels of the truck lift completely off the rail - completely losing contact with the rail and the unit stops. 

 I have tested with both FasTrack operating track as well as the PostWar style tubular operating track - the result was the same.

I have 5 RailKing diesels locomotives (TrainMaster, RS-3, F3) and three RailKing steam locomotives that operate fine.

The operating track is on the main loop so the two premier locomotives are currently not usable on the layout.

A search of the forum turned up two recommendations - the first was to reduce the bulge of the magnet on the FasTrack section - I tried two separate FasTrack operating tracks and the tubular one, so I do not think that is the issue.  There is really no way to reduce the height of the tubular track magnet and it does not seem to be raised any higher than the center rail.  

 The other recommendation was to replace the rollers with MTH part number BD-0000097.  I looked at the part description on MTH's site and it says the size of these rollers is 6.0 x 10.8mm.  I measured the rollers on my two locomotives with the issue - I get 6.5mm diameter with calipers so I suspect these units have the BD-0000097 part.  The rollers I have also have the black ends which I believe are plastic insulators.

 I checked the roller movement.  They all seem able to move freely - both rolling and arm movement with no binding.  The roller axle had a few drops of conductive lube per the MTH manual.

I talked with MTH support - the person I spoke with suggested it was a bad (weak) spring in the roller assembly and the assemblies should be replaced but he could not provide a part number for the replacement.  After the conversation I was not confident of the diagnosis.  I do not think the problem would be a bad springs on two new locomotives, and if anything the spring would seem to be too strong in that it not allowing the roller to lift enough.   It also happens on both trucks - moving in either direction which would be 4 bad roller assemblies.  Before spending $40 + shipping on new rollers, I wanted  to see if anyone else here may have any suggestions.

Any thoughts are appreciated.

Original Post

I had the same problem with my 4 wheel truck premier locomotives(6 wheel truck locos work fine). I pushed the whole uncoupling mechanism down, which helps, but I eventually just removed them from the mainline. I am using o27 track

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