Issue with Vostok Amphibia Amplitude

[Marcus]

Hello!

 

A watch that I have stripped apart many times has presented with an issue. It is a Vostok 2416B movement. 

 

There is significant variation in the Dial Up and Dial Down positions of the watch when tested on a timegrapher.

Dial UP = + 15  seconds a day

Dial Down = -56 seconds a day

Both positions show an amplitude of around 256° and a beat error of 0.1MM

Any regulation of the balance will fix it in one position but throw it way off in the other. 

The only modifications I have made us the installation of a shunt under the balance cock due to no end to end play with the balance staff (it is a bit too big) which solved the amplitude issue, as the balance was binding when the cock screw was tightened.

 

I am wondering what could be causing such a variation? I have checked both balance jewels for damage or dirt and have cleaned them, same with the balance staff, hairspring and to no avail. I have reoiled it several times using differing viscosities of oil and nothing has changed.

Thank you :).

[spectre6000]

You already identified that your balance cock shim is on the thick side. Too much endplay means the balance can physically move enough that you might be distorting the hair spring a bit. 

Alternatively, a quick google shows the spec on that movement from Vostok is -20/+60 S/d. Mayhap some of that is in manufacturing tolerances rather than regulation? 

[watchweasol]

Hi check that the play in the staff is not too much causing the shoulder to rub on the setting.  The fitting of shims is not standard practise, it needs a new staff to be right.  cheers

[spectre6000]

Thoughts on shims and doing things right... Yes, a new staff is definitely the right way, but what if this watch isn't worth the effort or expense? 

A hammer blow might be enough to thin out the shim depending on what you used. Alternatively, a light pull across some emory cloth with a finger on one end might be sufficient to change the angle of the cock just enough to open up the end play a bit without messing too much with the rest of the balance geometry. It's hacky as hell, but sometimes that's the best answer. Zip ties make excellent spark plug wire separators, even in show cars. Just sayin.

If it were an expensive watch or a customer watch, absolutely. New staff. No question. What if this Vostok is just for goofing off? No reason to go to that length unless that's what's truly needed or desired. Sometimes, you just want to see if you can get it going again.

[Nucejoe]

Move the shim as explained above to adjust the end play to .02mm or so, if no significant equalization, an issue at pivot exist usual suspects are, burr pivots,  slightly bent pivot, fresh oil mixed with old remianed in jewel hole, worn flattened pivot where it sits on end stone.

worn or slightly cracked jewel hole, different jewels on each side, excess side shake at one end etc.

Visual check under high magnification and elimination are approaches at your disposal.

 

[watchweasol]

Hi Yes I get your point, the only other thing to do is to reduce the thickness of the shim and go through points raised by Nucejoe.    good luck