I also have a couple of Bachmann 2-4-2s - one of which has been a real pain in the proverbial - and had a look at them to see what could be done. My little Wite Pass loco only needed a good clean - particularly at the back of the driving wheels which have carbon brushes - so that was tested OK.
The other, a coal burner in Penn colours, was a different kettle of fish. When I took the cover plate off this pre-(well)used purchase, I was surprised to find that there were no pick-ups from the driving wheels and no sign of there being any when made.
The axles are metal running in the plastic 'bearing', whilst the motor block has provision for skates (but no mounting holes or connections), the cover does not. There have never been any brass contact strips on the inside of the cover plate either as there is a shallow cast iron weight secured to it.
So, no wonder it was a poor runner! Just the two single axle trucks to collect the current! I had put a piece of lead on the leading truck to help but I didn't know about the pick-up system until I took it to bits!
Anyway, I converted the tender to 8-wheel pick-up as per all the others. I didn't bother cutting off the latching prong as the plug/socket was more accessible. Before re-fitting the cover, I drilled holes to allow the two wires to pass from the cab and through the cover. These were then soldered to the connectors on the truck.
It now works well. It cost me £4 (inc. post) for 4 metres of 1mm brass wire to make the contacts strips. Although the wire isn't as springy as the 1.0mm brass rod, it does work OK if the wire is over bent. So at £0.50 per loco it's a very cheap do!