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    Rory formerly worked as Curator of Horology at the Royal Observatory, Greenwich, where his role included day-to-day management of research and digitization projects, writing, public speaking, conservation, convening conferences, exhibition work, and development of acquisition/disposal and collection care policies. In addition, he has worked as a horological specialist at Bonhams in London, where he cataloged and handled many rare timepieces and built important relationships with collectors, buyers, and sellers. Most recently, Rory has used his talents to share his love of horology at the university level by teaching horological theory, history, and the practical repair and making of clocks and watches at Birmingham City University.

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Mainspring Size Question

Dan13

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Jan 21, 2021
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I purchased a restored Seth Thomas 89 J movement from a person on eBay that had restored it )Put new bushings in, cleaned it, new springs, etc.). I just popped my old movement out and plugged this one in and it worked great - for about two weeks. The second time I went to rewind the 8 day movement there was a loud BANG and I found my mainspring sprung. I emailed the seller, and he had me send the movement back and he put a new one in for me (for an additional cost) as I had no tools to do it myself. The clock came back and I plugged it back in and it runs fine and has for years. However, after about 6 days it wants to stop. In looking at the movement the strike spring is mostly unwound as is normal after several days, but the new mainspring the guy put in is still wound tight with only the last few outer bands showing any real gaps. I oiled the springs with Mobil 1 5w-20 oil as I usually do and when I wound it up tight a tad squeezes out between the springs throughout the coils, so I am pretty sure this is not an issue with the mainspring sticking - it just does not unwind much at all.

Since it lasts six days (even though the spring still looks tightly wound) I am not sure what to think about this, and I could find no other posts on this. I would not think it would be "set" as it is fairly new. Is this normal?
 

bruce linde

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maybe the new one he put in was a little shorter than it was supposed to be? you would have to disassemble to measure, as you would need to verify length and thickness.
 

bruce linde

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I guess it is always possible the new spring was not so new. Do you have a way to let down the spring?
my first thoughts was that maybe the mainspring broke near one end so he just re-worked that end and re-purposed the thing... a tad shorter.
 

Dan13

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Bruce - Well, the wound up size it the same diameter as the strike spring coil size when wound as well - it just does not seem the "unwind" much. I am not sure how it runs 6 days and does not unwind much at all.

Murphy Fields - I do not have a way to let down the spring tension other than just let it go without a bob attached. If there is a cost effective solution/tool to do this I would be up to it if it is needed.
 

murphyfields

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This is the type of tool you will need...

Let down chuck.

You can just buy the size you need, or a collection. But you will want a handle. It is also possible to make one with a large wood dowel and a key, but purchasing is safer.
 

John P

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Dan, make one for now out of a cut off section of a broom handle. drill hole in center to fit your key and saw a slot for the wings.. works fine.

johnp
 

shutterbug

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The symptom seems that the time mainspring was replaced, and might have been replaced with one longer than was called for, or one that had been used before. In either case, I don't think it would cause the clock to stop. The strike spring unwinds more, and I wonder if it might be somehow interfering with the time side, stopping the clock? That's the only scenario that makes sense here. Does the strike spring unwind outside of the clock, or does it seem to unwind inside? Could you post a pic of the movement when it stops?
Edit: Rethinking this, maybe the time side mainspring is unwinding inside the movement and stopping it. A pic will help here. There should be a little tab that prevents that from happening, and often they are broken off.
 

Dan13

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The spring stops are in place so the springs cannot expand inside the movement or to the other springs. When I say the strike side expands, it is puffing out the side just a bit and the time side mainspring still looks wound.

As a side, I made a let down tool based on your suggestions. 20210122_091403.jpg
 
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shutterbug

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I'd set the key a little deeper for safety. Still would like pics of the movement when it stops.
 

howtorepairpendulumclocks

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Hopefully the repairer retained the original springs they removed. If they have and they are not broken, get them re-fitted. Likely, all will be good.
 

Dan13

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I had the mainspring replaced a few years ago by a guy I bought the movement from on Ebay. Would be better off just replacing the spring with a new one if that is what is needed.
 

Dan13

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As Shutterbug requested, here is the pic of the mainspring. I wound it to stop last Thursday at 7am, and here it is 8 days later Friday at 2pm. Some notes - the clock was still running, I just stopped because I am about to be gone for 5 days. Also, I turned the strike spring 4 half turns after 5 days, and again after 7 days because the strike was moving slowly (a total of 8 half turns in 8 days).

As you can see, the time spring is still pretty tight, while the stike spring is unwound quite a bit even though it was rewound 8 half turns in the same duration. Any idea why the time side spring is staying so tightly wound even though it runs 8 days fine? 20210129_141709.jpg
 

Willie X

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On some S-T 89s the strike side rotates ~ 10 turns in 7 days but AFAIK all of the time sides rotate ~ 7 turns in 7 days. Anyway, the spring should power the clock until it stops against something like the 2nd wheel pinion or shaft, or the stops that most clocks have to prevent intrusion into the movement.

Also, after an 8 day run, the spring will likely be ~ 1/2" smaller in diameter than the main wheel.

Willie X
 
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Dan13

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Thanks Willie, but my question is more about wht the time side spring does not unwind as largely as the strike side. It obviously has enough power to run the clock 8 days so not sure it is set. To remind everyone, this is a spring that was replaced by the guy I got this restored movement from because the one that originally came with the movement broke when winding two weeks after I got it from him. My curiosity is if the correct spring or length was used for this replacement.
 

Willie X

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Sorry ... I read your problem backwards.

You will probably have to take your clock apart, as bruce already mentioned, to find your answer. You could look up "Willie's Turns of Power. This will give you the exact number of turns your clock uses in a week's run.

Your problem isn't going to be the time spring. There is enough power left in that spring for another 4 or 5 days of running.

Willie X
 
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