Beat error in only one position?

[Levine98]

Title says it all--I have a vintage Bulova 11AC (manual wind, 17j) movement that I cleaned and re-assembled today and it times very well in DU, DD, CL, CR, CU positions (amplitude is between 250/210 in all positions with a beat error >.5 in the above positions). Lastly, it's timing pretty consistently in all the above positions (running about 60 seconds fast but I usually let it run for one full wind before making any corrections)

However it CD position, it maintains amplitude but jumps to a +5.0 beat error.

I've let it settle in for a couple of hours since re-assembly and re-oiling. I did inspect every part under my microscope before re-installing, and hand cleaned the movement (my ultrasonic is out being repaired). So on the surface I'm pretty confident that the parts are clean and no obvious imperfections.  

I've included most of the timegrapher shots, most importantly the first one, i..e,  the one that is way off crown down.

Levine98

Edited August 11, 2022 by Levine98

[Neverenoughwatches]

4 hours ago, Levine98 said:

Title says it all--I have a vintage Bulova 11AC (manual wind, 17j) movement that I cleaned and re-assembled today and it times very well in DU, DD, CL, CR, CU positions (amplitude is between 250/210 in all positions with a beat error >.5 in the above positions). Lastly, it's timing pretty consistently in all the above positions (running about 60 seconds fast but I usually let it run for one full wind before making any corrections)

However it CD position, it maintains amplitude but jumps to a +5.0 beat error.

I've let it settle in for a couple of hours since re-assembly and re-oiling. I did inspect every part under my microscope before re-installing, and hand cleaned the movement (my ultrasonic is out being repaired). So on the surface I'm pretty confident that the parts are clean and no obvious imperfections.  

I've included most of the timegrapher shots, most importantly the first one, i..e,  the one that is way off crown down.

Levine98

In the first photo the readings are all over the place, escapement issue ? Most noteably the amplitude is way up as well as the beat error increase. Another inspection of the escapement and running of the balance assembly. How is the hs looking when running ?

[ifibrin]

If there’s a beat error in one position that’s vastly different from the other positions, I would look at the hairspring shape, and whether it’s rubbing against something, or out of round. That has a tendency to cause a beat error when the hairspring is in a specific position.

[Nucejoe]

Excessive side shake on balance staff.  

[nickelsilver]

You have a really noisy line on one side of the escapement in CD, I would check in particular the fork horn and guard pin freedom on the entry side. In that position the sideshake of the balance will reduce the freedom on entry side.

 

I wrote a basic checklist of the escapement here.

[mikepilk]

It is showing 60° more amplitude CD than dial down. I suspect that the timegrapher reading could be in error (weak signal?). This could be causing incorrect amplitude and beat error being shown. (Similar to the problem I think I'm having in my recent post!)

[Levine98]

9 hours ago, Neverenoughwatches said:

In the first photo the readings are all over the place, escapement issue ? Most noteably the amplitude is way up as well as the beat error increase. Another inspection of the escapement and running of the balance assembly. How is the hs looking when running ?

I studied the hairspring under a microscope while running (usually the first thing I do). Appears to run flat and without any visible distortion while swinging. Re it does seem to run high in CD position but this imposture captured it at the highest — normally closer to 250-260 when it settles down.

8 hours ago, Nucejoe said:

Excessive side shake on balance staff.  

I’ll check later today—thanks for the suggestion.

[nickelsilver]

I think you will be able to visually see that in CD it's likely running a much lower amplitude- like half the 290. The machines sometime double the amplitude when things are noisy (like a guard pin rubbing, hint hint).

[Levine98]

2 minutes ago, nickelsilver said:

I think you will be able to visually see that in CD it's likely running a much lower amplitude- like half the 290. The machines sometime double the amplitude when things are noisy (like a guard pin rubbing, hint hint).

I just went through the checklist—will challenge my skills for sure—I’ve fouled more balance wheel and hairsprings trying to sort out issues (usually a non-flat hairspring) than actually fixed any—but I guess you have to jump in the pool if you’re going to learn to swim….. thanks 

[Levine98]

Well I let it run through the night then gave it a full re-wind. Seems to have resolved itself. I'm going to assume oil hadn't set in or worked itself off some part of the escapement.

As before, running well in the other positions. 

Thanks to all (as a hobbyist, it's nice to have one work after servicing). 

 

[Neverenoughwatches]

4 hours ago, Levine98 said:

I just went through the checklist—will challenge my skills for sure—I’ve fouled more balance wheel and hairsprings trying to sort out issues (usually a non-flat hairspring) than actually fixed any—but I guess you have to jump in the pool if you’re going to learn to swim….. thanks 

Absolutely levine, you cant learn if you dont do mate