7S26 Woes

[Davey57]

I have had an old Seiko S Wave that I bought lying around for longer than I care to remember and thought I would see if I could get it going. The watch itself was in very good condition and the movement looked as if it had never been touched before. It would run for about 10-15 seconds before stopping. Thinking it would maybe just need a clean and service that is exactly what I did only to find it was just the same. After gradually taking bits out and putting it together with as few parts as I could to try and find out what was going on I noticed that when it was wound, the barrel kicked up slightly and was rubbing on the centre wheel bridge. The wear in top pivot hole for the barrel did not appear that excessive and looking at how new the movement looked I was quite surprised that this was the trouble. No worries I thought, I have some parts from an old movement that might be in better condition. Although it was from a much older and tattier looking movement, after cleaning etc I tried the top plate on and it was a big improvement and the movement now spun much more freely than before. Put it all back together and, ...... it was just the same. Getting a bit fed up with it by now I left it for a while in order to have a rethink. Starting again it looked like everything was fine up to the point where the balance came into action. Like the rest of the movement it appeared brand new, I had stripped and cleaned the cap jewels and checked the pivots which looked ok to me. But it just did not have much "life" in it, and seemed sluggish and slow, giving it a spin with the blower it moved well enough but at rest I could move it about 1/10th of a turn and it would just stay where I pushed it. On one occasion as I was removing the balance once again to have a look at it the damn thing started to run, but bizzarely it was only sitting on it's lower pivot as I had the balance cock hovering in mid air in my tweezers! The only way to be sure would be to swap the balance for another, but the only one I could possibly use was in one of my good watches. I was a bit reluctant to start borrowing parts from a good watch just in case I had a mishap and ended up having another dead watch. I was so frustrated by then that I just wanted to find out for sure what was wrong, so I took the plunge and borrowed the balance from my good watch. It immediately began to work like a goodun. So I don't know what is wrong with the balance, I put it into the other watch just out of curiosity and it performs like it did in the other one. I have had the cap jewels out again and looked as closely as I can at the pivots but can't see anything obvious. I am wondering whether it might have a very slight bend in one of the pivots, but even lying upside down with only the top pivot located it just does not move like any other balance I have seen. It is like all of the spring has gone from the hairspring, if you know what I mean. Sorry I did not take any pictures but I did not expect it to turn into such a performance. But at least I know it works now, I have put the balance back into my good watch so I am on the lookout for a decent balance now, if anyone has a spare they don't need I would be very grateful. Otherwise I will try and find another donor watch.

[Geo]

Interesting Davey, like you I think you may well have a bent pivot.

[Marc]

Interesting Davey, like you I think you may well have a bent pivot.

+1 on the bent pivot theory

[jdm]

I think you would need a microscope and micrometer to appreciate faults in balance and stones. The hairspring is easier to diagnose with pictures. Also i understand you don't have a timegrapher, although an extremely limite amplitude is easy to to see anyway. It's when it's about 150 deg and erratic that you need the machine to tell go / no go.

[frenchie]

Any chance the hairspring is not flat, rubbing on something maybe ?

Another idea : is the balance wheel flat (is it perpendicular to the staff)? The pivots could be straight but the balance wheel not flat (I've had this happen with a bad balance staff replacement)

[Davey57]

Looks to be flat, set it spinning with the blower and looked at it edge on and it seemed true. Hairspring also looks ok.

[frenchie]

I'm just guessing here, but could the balance staff be too long? 

[jdm]

I'm just guessing here, but could the balance staff be too long?

Unlikely. More possibly cap jewels installed upside down, producing the same effects.

[frenchie]

Unlikely. More possibly cap jewels installed upside down, producing the same effects.

 

Yes, very good point! Easy to test too : remove the jewels, see if the balance moves :)

[Davey57]

I'm just guessing here, but could the balance staff be too long? 

 

Doubt that it could be too long as it was the original and it looked as if it had never been disturbed previously.

 

Yes, very good point! Easy to test too : remove the jewels, see if the balance moves :)

 

Yes tried that too, checked and double checked, the jewels were not upside down. Even with the top jewel removed it would not work. The only time it tried is when, as I say, the balance was sitting in the bottom pivot and the balance cock was in the air held by my tweezers. So maybe the top pivot is the culprit, with a slight bend?

[oldhippy]

I might as well have a go so I'll say its a balance staff pivot that for some reason isn't smooth.