I do not post here too often, as I don't have that many Chinese watches, but this time I have something suitable for the Forum.
In 2017 I bought a cheap Shanghai A581 remake to wear. I like the vintage looks of it and I think it's a great looking watch, and also… it's very inexpensive.
That's my watch here, and here's the review I've wrote back then:
Like I've wrote on Friday, the watch broke, so I got a chance to open it and see what's inside:
The poorly finished movement (not the worst I've seen, but the finish quality is poor) is the standard Chinese caliber made since 1970s.
As you can see, the problem is with the ratchet wheel that disengaged the crown wheel:
This should not be possible at all, so either the screw was loose or maybe it's because the ratchet wheel has too much play on the barrel arbor.
Examining it, yes it does have some play and also it's somewhat thinner than the earlier wheels I have in stock.
I was even thinking I could replace the ratchet wheel, but first, I just wanted to make sure it's needed to replace a part, so I reattached the wheel and that's where the real problem started.
Usually when I screw down the ratchet wheel, I screw it down till it starts turning, then I wind up the watch and tighten the screw when it's fully wound (so that the ratchet wheel won't turn easily anymore.
OK, OK, because of the ratchet wheel problem I did use a tad more force than usual, and so - maybe I did put a tad too much force, but I'd expect the (very thin) screw thread to give in first in such case, while no...
The tightening of the screw caused two issues - firstly, I cracked the chrome coating of the screw (yes, the Chinese make chrome plated steel screws, believe it or not...).
That's a cosmetic issue, painful, but quite meaningless. The other thing was that oddly, the ratchet wheel advanced a few clicks ahead with an ominous sound coming from inside of the movement.
I was sure I damaged (stretched?) the mainspring, and the fact that the watch would not work anymore kind of confirmed it.
So I took the barrel apart, removed the mainspring (which looked good), relubricated the (DRY as Sahara sands!) barrel and used a different mainspring to make sure. However, the watch still would not run a bit.
So I put the original mainspring back in the barrel, and disassembled the whole movement to see what's wrong.
I just could not believe my eyes:
The center wheel lost a great deal of teeth!
I broke the center wheel with my screwdriver, by tightening the ratchet wheel screw.
It's just hard to believe, I'd not even think it's possible.
OK, maybe in a very, very small ladies' watch, but then again - I'd still expect the screw thread to beak first, not the center wheel!
I had an old Chinese movement in my drawer, so I took a replacement wheel from there.
It's in near perfect condition, so I could use it to repair my watch.
I assembled the watch, but it would not run with the new wheel.
It seemed like now the center wheel would rub against the pallet fork, locking the movement.
I examined the wheel to check if it's all nicely flat (which it was), compared the sideshake and the endshake with the original wheel, compared the wheels - without any precision measurements, they looked the same, so probably there was just a micrometric difference between the two.
Finally I took the donor movement's pallet fork to compare, and again - it was all the same (but then again - I used just a magnifying glass to tell).
Actually I even intended to try the other fork for my watch, but the new one was al nice and shiny, while the old one... you know :)
So I assembled just the center wheel and the fork and I found the problem.
On the new fork, there was a thick, somewhat excessive, blob of shellac on the exit pallet.
I used a heated screwdriver to flatten the blob and reassembled the movement again (photo showing the blob before I flattened it):
The movement is of very simple design, actually very similar to most of the movements of this type (direct drive sweep second).
There is a separate bridge for the center wheel, then there are the 3rd gear and the 4th that's co-axial with the center, and then the escape wheel.
After reassembling (damn it, another screwdriver slip, but the notch in the pallet bridge screw is very shallow), the watch started running and it still after over an hour, so I think it should be fine now.
Pay attention to details and don't tighten screws too much.
I keep saying it and yet I sometimes tighten them myself :)
It's funny, the 'natural' urge to try to tighten a screw in such cases. It won't help, but one still gives it a try ;) .