Edited 20 Aug 2019 20:48, 3 years ago, edited by comtrain

Hi All,
Thank you for the great help. Today I went through the offerings and found the Peco code75 track to be faultless. At one stage I thought the wire operating the throw was a problem. Finally I propelled 20 Austrains 4 wheel wagons (S trucks) back into the two problem points quite quickly with no derailments. I then pushed them through as fast as the loco would run, and again they ran smoothly.
So its not the track, obviously.
I checked the loco and all wheels are within the NMRA standards fitting loosely in the gauge.
I spent some time watching the pony truck, and it seemed to me to be jamming and not rotating enough to track through the curve. I removed the pony truck, and it is obvious to me why it is derailing. A spring slightly larger and stronger than a coupler knuckle spring is sitting in a hole and the other end bares onto the pony truck. (or have I got that back to front?) Anyway the movement of the pony is limited to a few mm's unless the spring bends, which it does, lifting the boiler up and taking the weight of the front drivers.
The pony truck is metal, heavy and so I removed the spring. The rotation increased to about 6mm either side, and the loco goes right around the layout without derailing anywhere, including crossovers and medium double slips.
I don't like leaving the spring out, however I hate derailments more so.  I think it actually pulls better as well. Perhaps lifting the drivers was another problem, not yet noticed
Thank you all for your help.
Rod