A friend asked me to fix his Mantua 2-6-6-2. I've figured out that something is jammed or stuck, I suspect the plastic tubing used instead of universals between the motor and gearboxes is the problem. But I I can't see how to get the superstructure off so I can find our where the jam is and maybe loosen it up. The loco was a gift to my friend, I suspect the previous owner disassembled it and during reassembly jammed something. The exploded diagram has disappeared.
Any help appreciated.
Thanks.