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 :).