Mainspring replacement cautionary tale....Bunn Special.

Discussion in 'Watch Repair' started by PJQL, May 19, 2017.

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  1. PJQL

    PJQL Registered User
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    Jun 13, 2011
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    Hi all,

    Just thought I'd share with you my latest and first experiences with replacing mainsprings
    without the use of a winder.

    I'd actually recently done the same thing successfully with a Waltham 1883, but this last one was a late WW1 era Bunn Special.

    The original spring had snapped in no less than three places! I sourced an alloy replacement via eBay from the US which arrived very quickly...except I got hit for a customs charge :-/
    Exposing and removing the barrel was an easy job...and so was removing the old damaged spring.

    After cleaning out the barrel, it just remained to insert the new mainspring, which was conveniently supplied preset in an aluminium transit ring. Hey presto into the barrel it went...perfectly :)
    Until in my haste I realised I'd put it in the wrong way...GRRRRR!
    And that's a really serious lesson learned.....

    Fortunately I managed to remove it very very carefully without damaging or distorting it.
    Now to wind it back up again manually. I wore a pair of surgical gloves to do this, which made it easy to start with, but much more difficult to maintain it wound up enough to reinsert it into the transit ring. But persistence paid off and I managed to persuade it into the ring, and then on into the barrel it went.

    Reassembling the watch was a straightforward job, and now it runs perfectly...Phew.

    The morale of the story is of course to check that the spring is inserted the right way before committing yourself to inserting it into the barrel. I guess that I'm not the first...and won't be the last!

    Hope this was useful..in its' own small way!

    Regards

    Piers
     
  2. roughbarked

    roughbarked Registered User

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  3. glenhead

    glenhead Registered User
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    Nov 15, 2009
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    Yeah, after putting the second mainspring in backwards several years ago, I started at least making a quick sketch of the center coil or which way the remains coiled if the spring was broken in the barrel. I nearly always take a picture of the spring in the barrel, but always always always make a sketch. Compulsive? Maaaaybe...

    Glen
     
  4. MrRoundel

    MrRoundel Registered User
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    I do the same thing as Glen does. Not compulsive, prudent. The fewer times you mess with mainsprings, the better. Live and learn.
     
  5. Accutronica

    Accutronica Registered User

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    I wouldn't know. The CSOW course showed me how to remove mainsprings the proper and easy way. Also I bought some mainspring winders that make the job of installing them a cinch.
    Also, you're not wearing gloves in the second photo.

    Robert
     
  6. Kevin W.

    Kevin W. Registered User

    Apr 11, 2002
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    I have done the same before, it happens. Are these springs pre lubed, no need to clean before installing. You have a really nice watch.
     
  7. PJQL

    PJQL Registered User
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    #7 PJQL, May 19, 2017
    Last edited: May 19, 2017
    Roughbarked/glenhead/MrRoundel....Thanks for the input everyone!

    Hi Kevin....Thanks!....And no I don't think they are, but I'd always clean the barrel out anyway now.. think I read that

    somewhere here on this forum.

    The alloy mainsprings are allegedly supposed to operate better...but because it's my first one, I can't really comment yet.

    Maybe someone else has experience with them.

    Piers
     
  8. PWfanatik

    PWfanatik Registered User
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    If not using a drawing, I make a point of putting the arbor in the barrel, and making a strong mental note of which way the inner coil needs to run for the spring to work right. If I need to use a winder, I just put the winder down on the spring while I have it laid out in the correct direction...
    Dave.
     
  9. glenhead

    glenhead Registered User
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    Piers, the thing about modern alloy mainsprings is that they're more predictable over the long term. The alloys they use are more resistant to becoming "set", where the spring loses its tendency to return to its original shape. That helps it provide a more even power across its usable length.

    Most modern mainspring alloys are also immune to corrosion. The old blued steel mainsprings frequently break because a sometimes-invisible bit of corrosion sets in and weakens the spring. Once a spring fails in one spot, it's pretty common for the shock to cause it to break in multiple places.

    I have several dozen new-old-stock blued steel mainsprings that I'll never use. None of the sachets has been opened and they've all been kept clean and dry, yet many of the springs have turned to powder. Of the ten or so I've tried, only one survived its first winding.

    Glen
     
  10. PJQL

    PJQL Registered User
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    Thanks Glen,

    I guess that's progress. Old original mainsprings should be collectors items!
    Thanks for your input :thumb:

    Piers
     
  11. Mindless

    Mindless Registered User
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    Yep been there done that. Pictures and a sketch and a last second check to be sure. :)
     
  12. roughbarked

    roughbarked Registered User

    Dec 2, 2016
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    I've never seen this. I am talking about mainsprings that have been in the shop stock for at least 80 years. I can't really be scientific about this other than to suggest that the sachets weren't intended to stay wrapped around the mainsprings that long.
     
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