I have just disassembled a Bachmann J39 to fit a DCC decoder, it used to run fine before, but now it seems to have acquired a tight spot in the revolution of the wheels. I'm not entirely sure how this could have happened, I certainly haven't been fiddling with the wheelsets. I suspect the quartering may have gone off slightly, but am not sure. Any advice on how to correct this?
BTW, fitting the decoder wasn't that easy. Had to put it in the tender eventually and channel the wires to the loco. Then there were also problems where the connection on the motor was managing to get a feed from the chassis, despite being isolated. Turned out the plastic coating on the DCC wire had a split and was touching the motor casing's metal, which in turn had contact with the chassis...