I have two model 57 15 jewel Waltham PS Bartlett key winds. The watches look identical. One c1873 the other c1870. The balance wheel on the c1873 spins much faster,and farther than the balance on the c1870. I have cleaned and oiled them both,and both watches keep very good time. My question,what causes the difference in balance action between the two watches. My guess is different hairspring tensions,and balance wheel weight. Am I guessing right?

Cecil - I am not yet very knowledgeable about these sorts of issues, but will throw this out all the same. Could the c1873 be a quick train? I think that could account for the faster balance action.

If one is a slow train and one is a quick train, you can tell by placing one on your ear, and after a few seconds to "learn" that cycle, put the other one on you other ear, the difference will be obvioius.

Cecil, If the watch has adjustable banking pins, and I think it does, they may have been disturbed at some point in time. That can cause a big difference in balance wheel motion. The banking pin adjustment is very critical . I just ran across this in servicing a 12sz Illinois that had the same problem (poor motion). The Henry Fried watch repair book does a good job of explaining how to adjust them properly.
Harold

Mary Ann,and David, Thanks,I hadn't considered that it might just be normal. I listened to both watches for a while and both seem to have the same beat. Only difference seems to be the c1870 has some kinda extra noise in there. Kinda a very light "ting" on one side of the beat. Boy,that ought to give me something to think about for a while. But,with a quick thought, Maybe Harold is onto something. Maybe that "ting" is the pallet fork hitting the banking pin on one side. Although,thinking some more,(boy this hurts)seems like if the banking pins were upsetting the beat,then the time keeping would not be good.

The mystery is solved. I just couldn't stand it. I took the slow motion watch apart again,and I don't see how I missed it the first time,but the center wheel arbor was too tight in the bottom plate. It was dragging the mainspring power down. A couple of light passes with a fine round broach file and it fit just right. I don't know why it was so tight,or how it still kept time with the balance moving so slow. Someone may have replaced the center wheel at one time. Anyway,it now runs just like the other one,and still keeps good time.

Cecil - glad to hear that you figured it out! I'll have to file this one away in case I encounter the same thing as I have several model 1857's.