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Hi, I have a Rotary Monza I am fixing up. I disassembled the barrel and removed and cleaned the mainspring. I secured a copy of the parts list and it shows that as well as the mainspring, there is also a Brake Spring (part 775 on the picture). What is it, and do I really need it? Certainly Cousins does not sell it. I googled AS 1902 brake spring and ONE result came up of a Russian watch forum discussing this item. Apparently it is thicker than a normal spring and it seems to have some sort of bent over feature on it. Can I just make one using the old mainspring? If so, how long should it be? Is it really necessary? https://translate.google.com/translate?hl=en&sl=ru&u=http://forum.watch.ru/showthread.php%3Fp%3D5196915&prev=search ROTARY Monza AS 1902.pdf
Here is my puzzle. I have a watch that I am working on. A Hamilton 987. It has been cleaned and oiled and demagnetized. When I run it on the timing machine the horizontal rates and the pendant down rate are all close and about +/- 4s/day. When I move it to pendant left things get weird. It has the same amplitude but the daily rate goes way off the chart -98s/day or something, also the beat error goes from 0.5ms to 0.0ms. The hairspring is running unobstructed, and he regulator fingers are adjusted correctly. How can this happen? How can a wheel spinning at the same amplitude produce such a wildly different rate? And how does the beat error change with the position change like that? Thoughts? Thanks Rob