There seems to be one person who unfailingly knows their way around the technical point of watches and is very generous with advice and education, so here it is: I have a cal 552 which was acquired by me. Serviced by an accredited Omega service centre and placed into a new case. After around 2 months it stopped dead. I sent it back and the mainspring barrel had come apart. The watchmaker reassembled the barrel and returned it but lo and behold it happened again a few weeks later. No knocks or impact etc.

After sending it in again he replaced the mainspring barrel completely. Since then I have been wearing it with no apparent problems except that today I noticed that if I rotate my wrist the way one does in order to look at the time that as the watch face comes into view the second hand momentarily stops then continues. This seems to happen mainly as the second hand passes between the 45 second and 20 second markers. At first I thought it was an illusion but this is not the case. Obviously I need to return it but I am very curious as to what the possible cause or causes might be. @Archer

 

Two separate issues I think. First the mainspring barrel is the container that the mainspring is held in, and the lid snaps on the barrel drum via friction. It's not unheard of for the two parts of the barrel to separate from each other, like in this Tag with an ETA 2824-2 I serviced recently - here you can see debris where the barrel rides on the main plate:



Here is the barrel:



And the lid has popped off the drum:



Note that this watch had never been serviced according to the owner, so whatever caused this to happen has it's origins at the factory, and not with a subsequent repair that wasn't done properly. Mind you, the watch was 16 years old and had never been serviced, so that may have something to do with it, and the big bill I handed the owner...

In your case it could be improper assembly of the barrel, or the barrel lid was just too loose - thinking the latter so that's why the repair shop replaced it.

With regards to the second hand, this series of movements use what is known as an indirectly driven sweep seconds hand. Here is a shot of a Cal. 750 that uses the same system with the automatic winding removed:



I had added some numbers - 1 is for the third wheel, and this wheel is what drives the sweep seconds pinion, which is number 2. You can't really see it here, so this is what it looks like out of the movement:



This is what the second hand is attached to, and the gear portion you see at the left end is what the third wheel (item 1) is driving. This pinion is sort of floating in it's hole, so the thin end goes through a small busing in the great wheel, but the end with the gear is just loose and not really contained, except by item 3 in my photo above, the friction spring.

As it's name suggests, the friction spring pushes down on the end of the sweep seconds pinion and provides friction on it. If this friction is not sufficient, you may see the seconds hand stutter a bit as it moves around the dial. The reason it will do this is because there is a certain amount of backlash/slack between the teeth on the sweep seconds pinion and the third wheel, so the teeth are not as fully meshed together as you might think. Now I can't see what you are seeing, but based on your description to me sounds like when you flick your wrist around, the weight of the seconds hand is causing the pinion to move and overcome the friction of the spring, so the hand may get thrown ahead slightly. When this happens, the teeth of the third wheel are no long in contact with the pinion, so the pinion (and hand) stops momentarily. Then as the third wheel comes around and takes up that slack between the teeth, before it starts moving again.

If that's what is happening, it's nothing very serious to fix, and it should just be a matter of bending that friction spring to put a little more tension on the pinion. I do think that even if it has the proper tension, you could maybe cause the same thing to happen if you flicked the watch around hard enough...

Hope this helps.

Cheers, Al

 

Thanks Al, as always a very clear and concise explanation. I recognize the parts you have mentioned and numbered from an exploded view of the movement from a posting I found somewhere and read through. Your explanation of the fault with the mainspring barrel is how I understood it to be and appears to be rectified. It is after all a pretty old movement to start with.

As far as the second hand goes I can't tell if it jumps forward slightly before coming to a momentary stop but your explanation makes sense regarding the indirectly driven sweep seconds pinion possibly needing a bit more tension from the friction spring to keep the teeth in continuous contact with the pinion.