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dreja

Too big amplitude &rate difference between positions

Question

Hello,

I'm trying to service a non working 7s26C movement.

I have dissasembled, cleaned and oiled it. I have also changed the complete balance. The old one was damaged beyond repair, so I purchased a non oroginal replacement from ebay.

The movement runs ok in "face down position", with amplitude about 270 and daily rate arround 0 sec/day.

When I turn the movement in the "face up" position, the daily rate drastically increases (about +80 sec/ day) but the amplitude drops to about 190 degrees.

When I move the watch bacj to face down, the thongs  get  normal anaing.

I have  mounted the same balance & bridge into another 7s26, but the behaviour is the same.

What might be wrong to cause such behaviour?

Is it possible, that I didn't properly tuned the hairspring with etachron regulator studs?

 

thanks Andrej

 

 

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7 answers to this question

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Check the cock jewel, end stone and its shock spring, shock spring should hold the jewel in place so it can not loosly move inside the housing. Slightly push on the said  end stone with your tweezers, should bring BW to stop. Also check if HS touches the cock or its spokes. 

 

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Hello, thanks for both answers.

I have already tried using another balance cock jewel with another jewel spring but the problem remains the same. If I press on the jewel, the balance wheel stops, so I suppose it should be ok.

I still need to inspect the hairspring rubbing, but in my opinion I would already see this anomaly on the timegrapher as "wired " lines?

In my case both timegrapher lines remain perfect (without "snow") and with minimum or no beat error...

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Did you get a good demag out of your demagnetizer?     Compass check.

The gentle push on end stone stopped the wheel, which generally indicates no excessive end shake. Most any BW can be brought to halt, if end stone is pushed down enough. Excess end shake can let pivots jump out of jewel hole.

How dose it behave crown up or down? 

 

 

 

 

 

 

 

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demagnetizing is a good idea but not sure its the answer to your problem since a magnetized movement will run fast in any position as well as a sticking hairspring, i am very familiar with the 7s26 movement but first thing that jumped out at me is you got an aftermarket balance. Not to mention it acts the same in a different movement so i believe your issue is the balance pivot or cock jewel. these aftermarket parts are not well made and if you were to look at the pivots from the OEM to the AF you will notice differences in the pivots. not to mention the quality control from chinese knock offs, i wouldnt be surprised if you had a cracked cock jewel or one clogged with oil and debris, i have seen flakes of skin in NEW chinese movements if you can believe it. i would check the cock jewel under 50x or more magnification. also remove end stone and spring and clean the balance cock and jewels, re-oil it and see if that makes a difference. 

Edited by saswatch88

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 Right, Indications are faulty pivot, derja begun with suspecting pivot/ jewels, why else would he have replaced the jewels on the cock side. So lets hope he didn,t spend thirty or fourty bucks to become the proud owner of a bad pivot. :blink:

Regards

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I presume you cleaned the other top jewel assembly befor installaţion, nevertheless, a droplet of avgas, lighter fluid, kerosene on top of the upper end stones will reach the pivots and temporarely act as lubricant,  as it may come to contact with possible congealed oil, as a result you will see considerable increase in amplitute...

I also gather if you had instrument for high magnification, you would have taken a close look at the top pivot when you removed the jewel assembly to replace. So we are limited to doing with what we got.

If crown up had indicated fault you would have mentioned it. Nevertheless, low amplitude with crown up or down means the fault is unlikely to be just at pivot interface with end stone. But is still indicative of possible bent pivot.

If you happen to have the balance out and off the cock with no high magnification available, there is a test we can carry out.  Regards

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