Hello Bob,
We have exchanged posts before. Not that it matters, but I enjoy seeing someone take these less expensive models and expend the energy to improve them, rather than just buying, six $250 locos and then complaining, at length, of the flaws they have found in them.
I have done work on less expensive lines my whole HO 'career', when I didn't have the money for premium stuff. I enjoyed the process of making them better.
I have reworked a friend's Bach NYC 4-8-4, to make it appear more like an FEF 2, which has one traction tire, and does a great job, pulling eight, 85' passenger cars. Also reworked the smoke pot, by adding a bit of cotton around the resistance post, so that it draws up the smoke fluid more efficiently. Smokes like a champ. This is essentially a Bach Plus model.
The most fragile Bach's are the 1975-80 units made in Hong Kong. I believe these were all ATSF Northerns & Texas types. These are good looking accurate models, Bowser made a chassis for. As mentioned, they have the three-part axle, which I describe as having the Bach 'dreaded eigth-coupled disease'. My fix went like this. Used CA on both sides of driver axle, maintained quarter while doing this. Didn't work (I believe epoxy is the glue answere here, although messier to work with). Next step, pinned metal nub on driver, through plasctic center axle on one side, maintained quarter. Worked, until other side broke loose. Pinned opposite side(eight pins). Somehow it appears I lost quarter. Little baby does not slip now. But has an evil hop. What do you think of redrilling drivers, one one side, to move rod pins into correct quarter positions, ? Would you have any interest in trying this?