Bad Mainspring?

Streetsnake

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Feb 28, 2021
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Hi all. I having been working on servicing a few PWs I purchased to practice on. One in particular is a Waltham 16s. It has been fully disassembled, thoroughly cleaned, oiled and reassembled. It runs well for about three hours after being fully wound and then stops. Is this a symptom of a bad mainspring or could it be something else? Thanks for any insights.
 

SpringDriven

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Dec 22, 2010
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That does not sound like a mainspring problem.

It would be a problem with too much friction for the mainspring to overcome after three hours of running.
 
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Skutt50

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Mar 14, 2008
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There could be a number of problems, e.g. a bent tooth on a wheel, a bent pivot, dirt or debree, crossing hands, escapemet problems etc. etc.

When it stops - What do you do to start it again? Can you make it run without re-winding it?

When it has come to a stop, I would firstly check if there is force on the center wheel. Push gently on the center wheel in reverse to check for some tension. Then by pushing gently forward you can check if the balance will take off.

You could also have a mainspring problem. Is the mainspring properly attached in the barrel? (When you wind, will it come to a complete stop when fully wound?) Is the mainpring barrel lid properly installed. Check so it hasn't come loose.

Once you checked the above, please report back.
 

Streetsnake

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Feb 28, 2021
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There could be a number of problems, e.g. a bent tooth on a wheel, a bent pivot, dirt or debree, crossing hands, escapemet problems etc. etc.

When it stops - What do you do to start it again? Can you make it run without re-winding it?

When it has come to a stop, I would firstly check if there is force on the center wheel. Push gently on the center wheel in reverse to check for some tension. Then by pushing gently forward you can check if the balance will take off.

You could also have a mainspring problem. Is the mainspring properly attached in the barrel? (When you wind, will it come to a complete stop when fully wound?) Is the mainpring barrel lid properly installed. Check so it hasn't come loose.

Once you checked the above, please report back.
Thanks for the troubleshooting ideas. I can get it going again for a bit by just giving it a little shake. There is force when I push back on the center wheel, however, when i give it a little "push" it doesn't start. I may be pushing too hard though?? I'm going to take it back apart this week to see how the mainspring barrel and such looks. It's seems like there is excessive friction somewhere. It starts out strong put it's power fades...more quickly when face down it seems too. Thanks
 

Skutt50

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when i give it a little "push" it doesn't start.
That is useful information. Try again with the balance moving a little. If it does not start then my guess is that you have a bent tooth on one of the wheels or some debree in one of the pinions.....

Firstly I would remove the minute and hour wheel just to exclude the parts on the dial side.

Check all teeth but in particular the center wheel and the mainspring barrel.

You can also do the following: Let down the mainspring. Remove the balance and pallet fork. Wind the crown half a turn and observe the geartrain. If it runs, listen carefully for the sound it makes. Is it "smooth" and even? The escape wheel should run, come to a complete stop and then reverse, at least a little. If it does, your geartrain should be OK.
 
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DoughBoyWatches

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Jan 5, 2021
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Thanks for the troubleshooting ideas. I can get it going again for a bit by just giving it a little shake. There is force when I push back on the center wheel, however, when i give it a little "push" it doesn't start. I may be pushing too hard though?? I'm going to take it back apart this week to see how the mainspring barrel and such looks. It's seems like there is excessive friction somewhere. It starts out strong put it's power fades...more quickly when face down it seems too. Thanks
what skutt said about testing the train and looking for that "reverse" in the escape wheel is essential with any movement service. However I think your issue might be in the escapement, the mainspring, or possibly a combination of both. A broken tooth would not cause a sudden loss of power. Since its loses power more with dial down tells me "escapement" issue so check the balance jewels for cracks and the end shakes on the balance wheel. If the mainspring is the original blue steel spring, that most likely will 100% be the issue because blue steel springs tend to take shape almost immediately after being installed, and those that have been coiled up in the barrel a long time loose a large amount of strength, which is why when you take them out they stay coiled up or in some cases start to cone upward rubbing up on the barrel lid. So when you fully wind it, it is at that point the MS will have the most power, enough to power the watch but as it unwinds it starts to slowly lose power until it gets to the point where its no longer putting out enough energy through the train to operate the escapement. And if you have a cracked balance pivot jewel this could make it even harder on your already worn down mainspring.

replace the mainspring.
 

DoughBoyWatches

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Jan 5, 2021
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Agree that a broken tooth would not however a bent tooth may definately stop the movement......
possible but also unlikely, however if it were to stop the movement it would happen well before 3 hours depending on which wheel has the bent tooth.
 

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