I earlier posted this question in another forum and was directed to post it here. I purchased a 2 rail Tennessean because I haven’t been able to find a 3 rail version. So I am hoping that it would be a feasible project to make the conversion. But one of the responders alerted me to the issue of minimum radius and the flat or flanged wheels vs track type. So I’m confused and looking for suggestions that would allow me to make the conversion….wheel change?
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So, there are several material factors at play here, minimum radius, type and quality of wheels, and type of track you are running on. Study all of those before you attempt any conversion, otherwise you might just be creating an expensive show piece.
I know that Weaver offered both 2-rail and 3-rail models of the same engines for years, but I don't know the intensity or depth of the design differences. Since 3-rail modelers usually considered these dual-made models to be of scale proportions, it is quite likely that the only differences were in electrical guts and grounding. But, they could also have had different drivers (O scale vs O gauge) and other wheels; I just don't know.
Whether certain wheels can run on certain types of model track is a function of track design (T-rail design like Atlas, curved top design like Lionel O27 or O31) and flange depth and width of the drivers and wheels as well as flange spacing on switches and crossings. So, if the 2-rail wheels are more scale proportioned (smaller flanges, etc.), they may only run well on Atlas-type track, and even Atlas switches and crossings require some modifications to prevent derailments.
Finally, I honestly don't think minimum radius will be a factor when moving to O gauge from O scale since many of the basic design features were 3-rail friendly (because the 3-rail segment is still the largest).
Chuck
Trying to make a 2 rail scale locomotive navigate hi rail can be a PITA , …..I wouldn’t advise trying to do it, ……but several schools of thought for what you want to do,….Weaver steam chassis aren’t exactly what I’d call the best anyways, ….they’re geared wrong, they’re motored wrong, and IMO, they’re just plain clunky running, …..if you want it to be a fine locomotive, with modern day electronics, ie; cruise, smooth starts & stops, and all the bells & whistles, then consider a full chassis swap from either a Lionel or MTH Pacific or even a Hudson that has the same dimensions as your Tennesseean ……if you wanna go the cheap route, I have these from a Weaver Pacific, I don’t think they’re from a Tennesseean, so we’d need to measure these, and then also confirm Weaver used the same frame for 2 rail vs. 3 rail,….these are 3 rail Weaver drivers,…..but again,…if that thing is as rare as you say it is, and you want to have the finest, I’d be chassis swapping it in a heartbeat,……for 3 rail, hi rail, whatever you’d like to call it, unfortunately, captured axles in a cast frame just can’t be beat for performance and longevity,…..either way, I can help,….
Pat 
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