SET MAINSPRING - Myth or Really Truely POSSIBLE ?

Discussion in 'Watch Repair' started by Brad Maisto, Jan 5, 2013.

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  1. Brad Maisto

    Brad Maisto Registered User
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    Oct 1, 2000
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    So I was given a 16S South Bend grade 317 to get back into "working" condition from an old friend who found it in a drawer with some of his other small vintage trinkets. The watch appears pretty clean, but upon receipt the mainspring was fully wound and the the balance wheel was "overbanked", if I'm using this term correctly? So now I have to wonder how long this pocketwatch has been fully wound, and knowing this person who has been collecting for many years, it could have been sitting like this for many years.
    I tried doing a search in this repair forum for "set mainsprings" without really finding too much prior discussion. I have seen where many repair people will automatically replace the mainspring when doing a routine cleaning?
    So I guess I'm asking if there is any type of instrument or tool to test the "strength" of the current mainspring, to see if it really has lost any of its "power" so to speak?
    And when a mainspring is considered "Set", what does this really mean?
    Thanks in Advance for your comments, opinions, and/or knowledge.
    Brad Maisto, Indiana Chapter 18 President
    P.S. This is the same friend who sold me a South Bend "294" in a solid 14K yellow gold hunter case that needed a dial. Good thing dials are interchangeable from watch to watch !
     
  2. Skutt50

    Skutt50 Registered User

    Mar 14, 2008
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    I usually replace the mainspring just in case.

    Otherwise to check if a mainspring is set you normally just look at it and how far it expands when let loose...... Now modern mainsprings are normally shaped differently than old and look like an S so you can not just compare a new and a NOS.
     
  3. klevay

    klevay Registered User

    Jan 24, 2010
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    Set mainspring is not a myth. A watch itself will be a test instrument for it. You won't get a good balance amplitude with a set mainspring. One can also determine if the mainspring has to be replaced by the the way it looks. Usually, if relaxed mainspring in the barrel has more than two coils around the arbor, it is set. Also, if you look at the out-of-the-barrel mainspring and its coil diameter is less then 2.5 barrel diameters, it most probably has to be replaced.
     
  4. sderek

    sderek Registered User
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    The main problem with a set mainspring is loss of power reserve.
    I was taught the 2.5 barrel diameter minimum, also, but I usually just check the mainspring in the watch. If it won't run for 24+ hours (with good amplitude), it's time for a new mainspring. But, you'd be surprised how many watches will run well, even with an old mainspring.
     
  5. psfred

    psfred Registered User

    Sep 25, 2009
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    Actually, a brand new carbon steel mainspring should look exactly like a modern white alloy spring, but long ago has lost the reverse curve and become a coil shape.

    Set springs have less power, so can cause fast running and reduced reserve -- a friend of mine had a watchmaker "save him some money" a couple decades ago by not replacing the mainspring in his 7 jewel Elgin. Had to wind it twice a day, although it kept time almost as well as his railroad grade watches. I dropped in a new white alloy spring and it works perfectly.

    "Set" means the spring has become bent, having lost it's elasticity. When you remove a badly set one, you will understand.

    My feeling is that one should always replace a blue steel spring with a modern white alloy one unless there is some important reason not to -- the customer demands an "original" spring even though the spring in the watch is very unlikely to be the one that came from the factory, there is no replacement and the watch will not be worn, etc.

    Any watch that is going to be used regularly needs a white alloy spring -- carbon steel (blue) springs will almost always eventually break, and in doing so damage the train and jewels. This is a risk I'd rather not take. I've seen broken white alloy springs in wristwatches, but they were all from the 50's. Worn out, yes, broken modern springs, not so much.

    Peter
     
  6. sderek

    sderek Registered User
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    I agree there may be a slight risk that a broken mainspring could damage a watch, after all, that's why the "safely pinion" and other features were introduced. But, I've been repairing watches for over 4 years, have changed countless broken mainsprings, and have yet to encounter a watch that was damaged by a broken mainspring.
     
  7. psfred

    psfred Registered User

    Sep 25, 2009
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    Well, it's impossible to say with absolute surety that the broken jewels in a number of 17 and 21 jewel watches I've acquired in the last few years were broken by the back-lash from a broken spring, but when I take a watch apart and the third wheel plate jewel is smashed and the mainspring is broken on the arbor end (and if broken on the barrel end, no broken jewels) it's hard to believe it's a case of everyone slinging the watch into a wall when the mainspring broke.

    I think alloy springs give better isochronism as well.

    Broken jewels from a snapped mainspring isn't something I've seen in wrist watches, but then again, not only are the springs much weaker due to the smaller size, everything post WWII seems to have white alloy springs originally.

    Peter
     
  8. Al J

    Al J Registered User

    Jul 21, 2009
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    I don't normally see damage to the movement from broken mainsprings, although I'm sure it can happen. However for purely performance reasons I always change the spring in a watch I'm servicing, regardless what type is in there when it arrives at my bench. If I'm putting my warranty the job, I don't want to put any faith in an unkown mainspring. The cost of replacing the spring is usually pretty small in relation to the price of the service.

    And although modern alloy springs are much less prone to breaking, I see broken modern springs quite often.

    Cheers, Al
     
  9. Brad Maisto

    Brad Maisto Registered User
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    So it looks like the alloy mainspring is not set, but upon re-assembly, the watch still seems to have an "over-banking" issue and after looking in Fried's Repair manual, I'm not so sure I want to tackle what could be responsible for this to occur? It appears the balance pivot jewels are okay, so is there a possibility that the replacement alloy mainspring could be too strong causing it to overbank? I'm including some pictures with this post, as I ran into another problem when trying to put the watch back together. The small screw for the the re-attachment of the mainspring gear was useless, see the one picture. Luckily I had a parts SB grade 260 movement that had the same size screw available. I was beganing to panic that the re-assembly was going to be foiled by this broken screw.
    SB.217.Mvmt.1.jpg SB.217.MvmtTop.jpg SB.217.SadScrew.jpg SB.217.DialTop.jpg SB.217.UnderDial.jpg
    It seems as though this watch was pretty highly finished at the factory, they even damaskeened both ends of the mainspring barrel. But i also noticed that there was a small amount of the barrel missing, it was where the cover re-attaches but even with this small piece missing, the cover seemed be attached securely. It was too difficult trying to get a picture of this. But thanks in advance for any further suggestions for me to get this watch working again.
    Brad Maisto, Indiana Chapter 18 President
     
  10. Skutt50

    Skutt50 Registered User

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    Here you can read some more about the shape of main springs and also a part of how to determine if a main spring is set: http://en.wikipedia.org/wiki/Mainspring

    I am not sure what you mean with part of the barrel missing? You may on occation find a shaved off thin piece of material but as long as the lid attaches securley it should be fine! (I am not sure where this comes from but I guess it has something to do with watchmakers who istall the mainspring by hand and the sharp edges of the mainspring shaves a tiny bit of the rim of the barrel!)

    If you have a well adjusted and newly serviced/oiled movement and install a new white alloy mainspring of the same dimensions as the old blue steel mainspring you may have an over banking issue. I have learned that the white alloy mainsprings are stronger than the old blue steel so you could try installing a mainspring some 2/100mm thinner to get rid of the banking problem.

    You were lucky to get the old screw out. When they break it can be a bit trickey to reverse the broken part out of the threads!
     
  11. sderek

    sderek Registered User
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    This may be a terminology problem. A watch that is over-banking will continue to run, but sounds like it is galloping, because the balance wheel has excessive amplitude, and the roller jewel swings around almost 360 degrees and hits the pallet fork on the opposite side.

    A watch that goes "out of action" will stop running because the roller jewel is on the wrong side of the pallet fork. Some refer to this condition as "over-banked".

    So, does the watch have an "out of action" condition, or an "over-banking condition"? True over-banking (the watch continues to run) can be caused be too strong a mainspring, but if a watch is truly "out of action", then it's an escapement issue, and the pallet jewels, and/or the banking pins, and/or the safety pin (dart) needs to be adjusted.
     
  12. klevay

    klevay Registered User

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    I was always under impression that condition you are describing is called "knocking"
     
  13. psfred

    psfred Registered User

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    Over-banking is a result of the failure of the safety pin to prevent the fork moving to the other banking while the impulse jewel is rotated away from the fork.

    The general terminology, so far as I can tell by reading watch repair books, is that an "overbanked" movement is out of action with the fork on the wrong side of the fork. The condition where the impulse pin hits the back of the fork because the balance is rotating too far was known as "knocking".

    Confusion between these terms may be a difference between how the conditions are expressed on the opposite side of the Atlantic, but all the older books I've seen call a watch out of action "overbanked" -- the use of the term to describe a watch with the impulse pin hitting the back of the fork seems to be a fairly recent event.

    Either way, the impulse pin resting on the back side of the fork is a safety pin problem, possibly made worse by improperly set bankings or pallet jewel locking (hence the "overbanked" term -- bankings set too far inward result in lack of locking).

    The impulse pin bouncing off the back of the fork due to over-rotation of the balance is far too much power in the watch or a serious miss-match between balance weight and hairspring.

    Peter
     
  14. Brad Maisto

    Brad Maisto Registered User
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    SDerek, you stated:
    "A watch that goes "out of action" will stop running because the roller jewel is on the wrong side of the pallet fork. Some refer to this condition as "over-banked".

    So this South Bend is out of action and also thanks for all of the replys. I will let down the mainspring one more time and replace the balance and see if it will run with a very slight wind.

    Thanks Again, Brad Maisto
     

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