The recent thread fantasizing how PRR 1361 should be restored brought forth another interesting issue. A poster included a scanned image from Staufer's Pennsy Power book, including an image of the two PRR K4s locomotives that recieved roller bearings on the driving axles and on the rods. The book states that the roller bearings used the existing pedestal openings.

I know we've discussed at lenght in this forum the inability of modern sealed freight car roller bearings to work in a steam applications (GSMRR 1702). If I remember that thread correctly, a pedestal opening on a steam locomotive frame is usually larger in size on a roller bearing equipped locomotive, compared to a plain bearing locomotive.

My question is does anyone know how the PRR managed to shoehorn roller bearings in an existing frame?

Maybe they used the "floating axle" roller bearing arrangement as used on the early N&W A's and Y-6's. With this arrangement, a single large diameter roller bearing is mounted in the hub of each driver. The inner race of this bearing rides on the outside of a tube that is mounted into the driving boxes. The axle rides inside this tube without contacting it (hence the "floating axle" name). The axle basically holds the two drivers in alignment and in quarter but doesn't support the locomotive's weight.

Since the bearings don't have to fit within the pedestal openings, it seems this would be a good arrangement for adapting to existing locomotives and maybe that's why Timken developed it.

You can find pics of the setup in the 1941 (and possibly earlier) Locomotive Cyclopedia.

I found a reference to this on pg 727 of the 1941 loco cyc. Are there any others in that edition?

Hugh,

Thank you for the explaination. It is much appreciated. I assume, even though Timken developed a work around, the cost wasn't justifiable to most railroads, given the fact that few converted? Then again, plain bearings were the norm on all types of equipment for years.

Joe- that's the only pic I know of. It took me a long time to figure out how that whole assembly is put together. I always assumed the 1218 had this same arrangement- it even has button head grease fittings between the spokes of the drivers that looks like they'd be used to grease an in-hub bearing. However, according to "N&W: Giant of Steam" by Jeffries, this setup was only used on the first few A's and Y-6's. Maybe somebody from the former N-S steam shop knows if this is correct.

wilkinsd- Glad to help. It may be that Timken soon came up with more conventional bearing arrangements that would fit in the existing pedestals of friction bearing engines; I just don't know. There are apparently were some drawbacks to the floating axle arrangement as N&W didn't use it on later engines.

It'd be interesting to tally how many locomotives had their driving axles converted to roller bearings. Many of these conversions were complete re-builds, including new cast bed frames, but surely there were a significant number that retained existing frames and added roller bearings. Maybe I need to break the Locomotive Cyclopedia out again...