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Lawren5

Shimming the Balance Cock

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I just serviced a Ball pocket watch with a Hamilton 992B movement. Prior to servicing, the balance wheel would not self start and the amplitude was at best 130 degrees when running. After servicing, the watch did not run any better until I loosened the balance cock screw just slightly which then allowed the balance to self start and the amplitude to jump to 210 degrees. The balance pivots look fine and I was careful not to mix up the top and bottom balance jewels. Given that everything else looked good, is shimming the balance cock an acceptable procedure and if so what is used as a shim?
 

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I just serviced a Ball pocket watch with a Hamilton 992B movement. Prior to servicing, the balance wheel would not self start and the amplitude was at best 130 degrees when running. After servicing, the watch did not run any better until I loosened the balance cock screw just slightly which then allowed the balance to self start and the amplitude to jump to 210 degrees. The balance pivots look fine and I was careful not to mix up the top and bottom balance jewels. Given that everything else looked good, is shimming the balance cock an acceptable procedure and if so what is used as a shim?
 

I would first take the balance off again and make sure the upper and lower jewels have no obstructions. Then I would see if the balance is round and flat. Then I would check that the impulse jewel is straight. If all this is good, check it the lower jewel is too high or past the setting, and if the upper jewel looks ok. Now if all this is good and you are able to shorten the pivots a bit using a jacot tool, do it. Last thing I would do is shim the balance, given balance staff is the right one, or the original. If you are nervous trimming the pivots, then shim.

Sent from my GT-N5110 using Tapatalk

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Russians do it all the time...I have taken apart several vostoks shimmed in this way and one or two old Japanese movements as well...no it isn't strictly kosher.but you don't know the service record either.out of tolerance parts may have been cobbled together.try a piece of Mylar

Edited by yankeedog
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Yankeedog - Good point about the service record. I suspect that the watch may have been serviced before as I had to replace the mainspring and the correct Hamilton one was several centimeters shorter than the one I replaced. It could be that the balance jewels got swapped in the previous repair. Well, I guess there's only one way to find out.

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I recently serviced a good runing vintage watch, with balance cock shimmed, Date written inside on the back plate indicated it was last service 18 years ago.

Shimming is acceptabls as long as the jewel holes on both ends of the staff remain in line or  shimming imposes no extra friction on pivots.and all else such as the  impulse jewel so on work uneffected.

You can shim to lower or raise the cock.

Oris indented a cross on the train bridge to raise the cock.

I can post a walkthrough, if this post is loved to death. 

Cheers.

 

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So the before servicing poor amplitude did you attempt to diagnose why it was poor or did you just assume that cleaning would fix the problem?

Then unfortunately with American pocket watches they've had quieted number of years worth people of service them and all sorts of bizarre and strange things can happen. Really common things are the banking pins usually get moved around. Then parts replacement parts they usually have to be fit if somebody did prior to you Replace the staff depending upon whether it was original or aftermarket the pivots very likely too long. This is where the easy fix is a piece of tissue paper under the balance wheel to get enough end shake. Otherwise shortening the pivot ends would be a solution that is once you determine that the end shake is a problem and there's not some other problem.

 

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I once bought a lot of vostok 2234 movements from Ukraine. From the looks of them they were stored in a hole in Afghanistan.I rather doubt they were serviced.about 1/4 were shimmed.I think it's just an expedient that gets used in high volume low cost units that the manufacturer wants to get out the door.

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I removed the balance jewels thinking that whoever serviced the watch before may have inadvertently swapped the upper and lower jewels but the lower set had a slightly larger diameter so they could not be swapped. It did appear that one of the lower jewels was installed backwards so I reversed it. This made a big difference in that the timegrapher line cleaned up and variations in both amplitude and rate were reduced when placing the watch in different positions. Still, I had to back off the balance cock screw about an eighth of a turn otherwise it slowed down the balance wheel.

I don't know if the balance staff is original or not but don't want to take the chance of shortening and possibly damaging the pivots. At this point, I'm tempted to go with the shim as the watch performs well once the balance cock is raised slightly.

In my original post I misidentified the movement as a Hamilton 992B when in fact it's a 999P.

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Then a note regarding shimming. The Russians because of poor manufacturing skills put an entire piece of metal under the entire bridge that's not needed here. All you need is a thin strip of paper on one side or the other of where the screw is. So you want to raise the bridge up put it on the inside. Then if you put on the outside will reduce the end shake. A nondestructive fix if you don't have access to the proper tools to reduce the pivot  length.

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1 hour ago, rduckwor said:

Didn't I see a video by Mark on a Chinese movement where they shimmed the balance cock by raising a knurl of the plate under the cock with a screwdriver?  It happens.

 

RMD

Seen that to. It was done from the factory. But as Mark had tighten the balance cook to much or to many times the knurl flatten out. After he redone the knurl it works perfect again. 

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