@David Johnston posted:
The worm wheels and the side rods are parallel drive linkages. Everything after these two locos used a single worm wheel and drives with the side rods. The question I have never been able to find anybody to answer is how close do the worm wheel teeth have to be in alignment with the side rod holes to get the front and rear driving axles to work together? You could just remove one of the worm wheels and you would have a drive train almost like ‘47 and later turbines and Berkshires. Or you could change the bad worm wheel and teach the rest of us how it is done.
David has more experience working on these locos than I do. Personally, I don't believe it would run very well with only one. Instead of trying to replace just the worm wheel, I would hunt around on auction sites, postwar parts dealers, etc., and try to come up with another geared wheelset. It should already have the bearing blocks installed too. A complete wheelset like this won't be cheap, but this loco is worth it!
The unique beauty of this design is that you can replace a wheelset without pulling or pressing anything. The bottom of the chassis comes off and you can slide the new wheelset right in, in place of the old one. Many fine brass models in all scales are constructed like this. My guess is that just replacing the worn worm wheel will restore the loco to factory operation. You should know in advance that these '46 models tend to run slower and with more noise than the later ones.
I understand exactly what David is saying about the "timing." If you get a new wheelset, please try to compare it with the worn one. See if you can discern whether the position of the gear teeth is the same relative to the driving rod bolt. In other words, is the bolt perfectly lined up with a tooth or valley? Is it off by the same number of degrees? Etc. I imagine that it will be difficult to measure precisely. However... if the timing of the front and rear axles are way off, the side rod will be trying to pull the wheel forward before the worm gear applies pressure to the next tooth, or vice-versa.
My guess is that they were all set up the same way at the factory (or should have been.) That's why I'm suggesting that you install a new-old-stock geared wheelset, and not try to replace the gear yourself. I've heard a million times that "some of these run better than others." I think the gear-and-rod timing might explain why this is the case. Look forward to updates on this thread!