Hello All,
I picked up a M1 Bulova at a thrift shop and everything looks really good and is running. I put it on the timegrapher and the amplitude is only around 200 degrees. Is that normal for these? I have only fixed a couple of elgin pocket watches up to this point and they had much higher amplitudes.
If it isnt normal do you all know what mainspring would fit this movement? Thanks
I'm not too sure about the appropriate amplitude range (would also like to know, I have one of these that will not run more than a day); but I believe these use a sealed lifetime barrel, so you would need to find a barrel complete and not just a mainspring - Bulova part# 1S (also used by the 10BZACD)
In reply to I'm not too sure about the… by Andersok
Oh, awesome. I might try to just take it apart clean it and oil it and see if that helps anything. Hopefully if I need to I can find that part. Mine only runs for about 30 hours.
I wore it for 2 days after I got it and it never stopped but once I took it off it ran for 30 and stopped.
In reply to Oh, awesome. I might try to… by wdschell
Ideal amplitude range would be mid to high 200's, 'perfect' is over 300, but I rarely see that in vintage watches. The better the amplitude, the better the stability of the timekeeping.
With these sealed barrel types, you can measure the mainspring and find one that is close in tolerance. Width is critical and should be exact, but strength (thickness) and length can vary slightly. That said, some of these Bulova mainsprings have no equivalent that is even close.
All bridle automatic mainsprings require braking grease (Glissalube 20) inside the barrel.