Hamilton PW balance stoppage

[arron]

Hi everyone,

Facts: I'm working on a Hamilton 16s Grade 974 PW.  Serial 2418945.  Before doing a coa, the watch ran well in the dial down position.  In dial up it would fairly quickly stop.  There was a lot of gunk on the upper pivot and I figured that was the problem.  After the coa, it continues to do the same.  I went through troubleshooting using another thread on this topic.  The only two issues I could find are 1) the spacing of the hairspring coils are closer together (but not touching) on one side than on the other side (I don't have a pic of that).  but when I took the hairspring stud off the balance cock the coils are equally spaced all around.  2) The upper jewel (the one that sits in the balance cock) has a slight indentation where the balance staff pivots has worn it away.

Other than that, the balance isn't touching anything, the hairspring lies flat, there is plenty end shake, and the pivots look good to me.

Questions:

1) Will such a small divot in the cap jewel cause the balance to stop.  I have no idea what the measurement of the divot would be.

2) Does the last loop on the hairspring look normal.

3) Why would the balance spring bunch up on one side, but be normal once removed from the cock.

4) Would the hairspring bunching up to one side cause the balance to stop.

Thanks for any guidance you can provide.

Arron.

[ManSkirtBrew]

Hi Arron. Disclaimer: I am a hobbyist and not a watch repair professional, so take my advice for what it's worth.

1 hour ago, arron said:

Questions:

1) Will such a small divot in the cap jewel cause the balance to stop.  I have no idea what the measurement of the divot would be.

2) Does the last loop on the hairspring look normal.

3) Why would the balance spring bunch up on one side, but be normal once removed from the cock.

4) Would the hairspring bunching up to one side cause the balance to stop.

1. I would say no. At worst it could lower the amplitude some.

2. It does from the top, but from the side it looks all wrong. It looks to me like it would foul the rest of the hairspring and cause it to stop oscillating. The Breguet overcoil should sit roughly parallel to the rest of the coils but on a higher plane. Yours looks bent in the opposite direction.

3. If the balance spring is bent near the stud it could push the whole spring off-center once the balance staff is in its jewels.

4. Unless it was very severe, then no.

Edited May 28, 2024 by ManSkirtBrew

[Neverenoughwatches]

1 hour ago, arron said:

Will such a small divot in the cap jewel cause the balance to stop.  I have no idea what the measurement of the divot would be.

Yes thats possible, that pivot could well have more friction when sat in the dimple, might be enough to stop the balance. If the dimple is deep enough and the staff pivot has worn down as well, which it most probably has then the staff could end up riding on the underneath of the balance jewel at it's shoulder height and stop the oscillations. 

1 hour ago, arron said:

Why would the balance spring bunch up on one side, but be normal once removed from the cock.

When the spring is removed it is only held at one point , at the collet on the staff, in this situation the spring is free to take on it's own natural shape. When fitted to the movement the spring is then held at 2 points, the collet and the stud, 3 if you include the regulating pins. In that situation the spring is being pulled from its natural shape if the 3 points are not correctly adjusted to match the spring's shape, usually just at the stud can bring things into alignment. Bunching up of the coils more often makes the spring oscillate faster, in effect taking the active timing point from the regulating pins to the bunched up coils , closest to the collet.

[nevenbekriev]

Hi Arron,

The hairspring looks pritty normal seen from above. May be You don't know how to fix the studd to the cock. See, this kind of studd carrier alows the studd to be placed to a different distance from the stone. So You don't need to pres the studd as much to the stone as it can, but let the spring take it's natural shape an only then tighten the screws of the carrier. Of course, if the radius of the overcoil is wrong, this will not help to make the spring stay as it should, but I doubt that You didn't do the things like as I just described.

The stoppng may be caused by different reasons. Yes, it can be pivot/stones problem, and it can be hairspring too. Of course, another possible reasons exist, like balance rubbing on the center wheel...

You need to make some checks to see what is wrong. I will advice first to remove all from the plate and leave only the balance assembly with it's cock. Then make free oscillations test in both horizontal positions and see what happens. Then, if the problem still there, remove the hairspring and put the balance only with the cock, then make balance turn and observe how it stops in both positions, if there is difference, and write here.

[arron]

Thanks for the replies guys.  In the process of following the advice above I think I discovered the problem which turned out to be operator error.  When I initially cleaned and reinstalled the cock capstone I pushed it as hard as I could and wondered why it wasn't flush.  I used a larger push rod (from my staking set) this time and got the jewel to sit flush.  Then after re-assembling the balance complete and installing it into the movement, it now continues to run dial up.  So having that capstone not touching the hole jewel fouled things up; maybe as was mentioned above the pivot shoulder was rubbing against the hole jewel.  The hairspring continues to not have equally spaced coils.  I have not timed the watch yet, but at least it is running in all positions.  I'm terrible at diagnosing watch repair problems (but if I know the problem, I can usually fix it) so this feels like a victory  .  It's the same as when I work on cars.  It's diagnosing the problem, not fixing it, that is my nemesis.  Wishing everyone well. 

[nevenbekriev]

What are amplitudes in positions, at least DU and DD? Running with no stopping still means nothing.

[arron]

30 minutes ago, nevenbekriev said:

What are amplitudes in positions, at least DU and DD? Running with no stopping still means nothing.

Hey @nevenbekriev thanks for bursting my bubble.  haha.  ok, you are right.  I'll get the numbers and report back; but mind you my expectations of my watch repair skills are rather low.   

[arron]

here are the numbers without any adjustments or lubrication (which I forgot to do).  dial down +31 211 6.9.  dial up: -110 185 7.8.

Can someone remind me which way do I turn the collet to adjust the beat error: if I'm looking at the impulse jewel from the front and the jewel is to the left of the left banking pin, do i turn the hairspring collet clockwise or counterclockwise when looking straight down at the hairspring collet.

[nevenbekriev]

You need to turn the collet counterclockwice if You need to move the balance clockwice. It is allways  the reverse direction that You need to turn the balance.

The difference in horizontal position rates is big, and in the same time the difference in amplitudes is not so big as to cause such rate difference. This makes me think that the hairspring touches something when dial up - look the bottom of the studd or overcoil can touch the cock

[arron]

Thanks so much for your quick reply.  I'll move the collet and check all clearances.  Have a nice day.

[Neverenoughwatches]

4 hours ago, arron said:

here are the numbers without any adjustments or lubrication (which I forgot to do).  dial down +31 211 6.9.  dial up: -110 185 7.8.

Can someone remind me which way do I turn the collet to adjust the beat error: if I'm looking at the impulse jewel from the front and the jewel is to the left of the left banking pin, do i turn the hairspring collet clockwise or counterclockwise when looking straight down at the hairspring collet.

Big beat error, this can make the watch slower to start running and end sooner, before the power reserve has ran out. Looking from the top of the balance, the collet needs to turn in the opposite way to which the pin needs to go. Imagine turning the pin itself ( dont do that or you'll muck up the poise ) now which direction would the collet move if you did that, simples.