AS984 Balance Staff selection.

[PostwarO27]

A few months back I took up a project to get an AS984 running.  I set it aside some time ago and am now just getting into it.  The watch isn't anything special, I just liked the dial and the hands.  The only issue I have in getting it running again is the balance staff.  It seems to bind when I cinch down the balance cock screw.  I have had the top and bottom jewels apart and cleaned at least three times and its still binding.

 

According my BestFit catalog, the length of the staff should be 3.07mm, however I discovered the one in the balance wheel is 3.3mm...obviously longer than it should be.  I figured I'd replace the balance staff with a new one of the length indicated in the BestFit catalog.  I went here: https://www.balancestaffs.com/a-schild.php for a new one but they're offering three different lengths.  The AS984 came with and without a shock setting and I know the staffs are different depending on the jewel setting type but none of them indicate which type of setting they're for. 

 

How would I determine the correct length?

[nickelsilver]

That site usually indicates which staffs are for Inca or whatever other weird shock system makes the difference, but not here. I would go with the mid-range one, 3.17mm, as your present staff is 3.30mm.

 

But- are your pivots straight? Are there "pips" dug in around your balance cock foot, or where it seats on the plate? (These are done to make the cock tilt up or down to fit an ill fitting staff.)

 

I've said before, I don't buy staffs, I just make them. Especially for AS or other prolific makers, for a given caliber you can have 6 or more possible staffs sometimes (AS 1012 !?), and between figuring out the right one, then crossing fingers the supplier sends that one, it's faster, and time-wise equal or cheaper (not counting postage!). I know most folks aren't set up to make staffs, but it makes my life easier, haha.

 

But in your case, I say go for the mid range? You can bend the balance cock a bit (seriously) if needed to make the final endshake adjustment.