I have a pair of those old Hornby (Triang) ? Shunters from the 60s. One works great, the other seems to run OK, but after about 5 seconds, smoke comes out and it would catch fire if left running. Could it be the magnet needs replacing or the armature needs re-winding ? It's the model that has the working front light. I have given it a service and cleaned up and oiled it. The light still works. Any help appreciated. Kev.