A couple more pictures. I managed to get the balance wheel and the large gear wheel behind it off. Not quite sure how I did this. The bolt is still firmly attached to the balance wheel. I tried to move it with a wrench but nothing happened. The bolt head is round, so it's hard to grip. Even as I was trying, I felt that this wasn't the right way to go about it. Finally I gave up and decided to just have some fun and see if I could make the balance wheel spin so I applied lots of sewing machine oil and kept rotating the wheel. It was getting really loose and smooth when I was delighted to see the gear wheel behind moving too! Finally the whole thing just worked its way off. I must have been turning the wheel backwards and somehow unscrewed it.
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The gear wheel has all its teeth intact, but the lip is either chipped or ground down. Still seems to fit, but it's not perfect. There should have been gold decals all around the balance wheel, but I can't see any trace of them now.