Per Ryan and Kelly's conversation above, one of the problems we faced with our 6 axle heavyweights was the switches they traversed. Too tight of a radius and it was destroying wheels and track components. One of the advantages of plain bearings was that we were able to narrow up the bearings on the center axle to allow more lateral travel without affecting the gauge. It made a huge difference. Before the work, if you coasted into a turnout with either of the heavyweights, as soon as all three axles entered the curve it was like applying the bakes. Afterwards it would glide through with a barely noticeable drag.

One potential 'treatment' that might be done with heavyweights is to adapt the center axle to use the kind of lateral accommodation in the early Timken versions of the trailing trucks to go on Berkshires when the articulared American Arch version started showing its little quirks.

In at least some of the Delta-type replacements, the location of the pivot to give correct Bissel geometry at the trailing axle did NOT give reasonable lateral for the forward axle; it could be thought of as a very long single-axle truck with a forward 'floating' bearing axle geometrically. To accommodate roller bearings in this, Timken worked up a system with a pair of hardened rollers over the journal boxes of the forward axle, with only the reasonable level of hub liners or cross-bracing to keep the bearings aligned to the axle. The pedestals were machined like the early Centipede tenders, with good wedges longitudinally but no formal centering on the axle between fixed stops on the boxes. Within those stopped limits the axle was free to 'float' laterally with gentle fillet and flange guidance while remaining fully weight-bearing under the equalizers, the contact surfaces top and bottom being ground and hardened like the rollers. I do not know how this was enclosed against dirt and cinders, etc. but a modern approximation would not require exotic materials or machining to work effectively.

[quote="Kelly Anderson"][quote="David Johnston"]In railway preservation the plain bearing if there was ever a mechanical reason that #611 would have to be retired, it would be due to a failure in one of her driving axle roller bearings, replacement parts being completely unobtainable.

As a former Timken employee:

The material is still made, the drawings and patterns are still on file; how many do you want and where do we ship them?

Dropping the Drive Axels and pressing off the drivers to replace the bearings is probably the bigger hinderance.