Got it! I am pretty sure my handling was a major contributor to this. But as I said earlier, the watch had an issue (likely with the hairspring) even before any handling. Could the hairspring really go bust even when the movement is cased? Something doesn't add up to me.
You need to detach the balance from the bridge to see exactly how bad the hairspring is, when it is still attached looks can be deceiving. The other thing I have spotted is someone has put two nicks on the bottom plate where the balance bridge sits and screwed down, this will affect the end shake to the balance and also the angle of the balance bridge.
I have had a watch with the Chinese Standard Movement suddenly die on me over a year ago. The issue is, the watch abruptly dies in certain orientations, even with a full power reserve.
I decided to open it up today and try to figure out what's going on. Since I don't really care about that watch, the outcome doesn't matter to me, it would be interesting to "diagnose" the problem as a starter. Prior to today, the watch was never disassembled once and the watch has has never been through any unusual beating.
While my methods of disassembly and handling might be a problem on their own, the watch had a problem to start with. I have tried removing the balance bridge and putting it back into place, but to no avail. Interestingly, halfway through a very gentle unscrewing of the balance bridge screw, the head broke off from the threaded part. I have dealt with smaller screws in the past, but never this problem.
In one of my attempts to put the balance bridge back into place, I got it to seemingly work, but the amplitude was visibly terrible.
In another attempt, I tried my best to center the balance wheel, but if I screw the balance bridge completely, it stops. The end shake seems to be reasonable, though.
The rest of the watch seems to be in a pretty workable condition.
This makes me feel it's an issue with the hairspring. The tiny pivots of the balance wheel appear pretty well intact. One thing, I did notice though, is that the spring is somewhat distorted such that the balance wheel is off center.
Attached is a video to show the issue. This is just after I removed the caseback. All components untouched otherwise. The pictures are taken after the handling and everything.
May I know what do you think of it?
The Problem in Video.mp4
Normally this check is done clean and dry, but clean and oiled is OK too. Ideally it should move with a blower but just moving it by hand will tell you if it's free. You need some endshake, not excessive, and as said above it shouldn't have too much "tilt", this is a sign that the holes need to be closed.
If holding with a pinvice you have to watch that the pinvice isn't influencing things. I prefer to capture the ends of the arbor in the flats of stout tweezers.