Hamilton Model 21 not unlocking

Discussion in 'Chronometers' started by watchwldr940, Sep 8, 2018.

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  1. watchwldr940

    watchwldr940 Registered User
    NAWCC Member

    Nov 26, 2008
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    Hello All
    As the title suggests, I have a Model 21 that is not unlocking. Here's the situation:
    I received a model 21 with a break circuit fitted that had not run in a very long time and was bought as non running. I've never seen so much goo on one instrument in my life, but that's another sideline for now.
    It had a bad staff with both pivots ground away on both the balance and escape wheels, as well as a shattered upper balance hole jewel. I had these (nos) parts in my small stock and was able to switch them out. I should mention here that I used a one piece double roller in lieu of the two piece that had been in the chronometer when I received it. After extensive cleaning I reassembled everything but it won't run--careful observation shows that when the balance it rotated counter clockwise the unlocking jewel will move the trip spring (and the locking jewel) out almost enough to unlock the escape wheel tooth, but not quite far enough and as the balance continues in that direction the locking jewel slides back down the escape wheel tooth and stays there. This is all being done slowly by hand. I don't want to jam the locking jewel so extreme caution is being used.
    So I am looking for some advice on how to proceed, and as of yet have done nothing more. I am thinking that I need to lengthen the trip spring to let it be carried that tiny amount further to allow the escape wheel to unlock, from what I have read. Would this be correct? There does appear to be sufficient clearance between the escape wheel teeth and the roller so the escape wheel looks to be correct. The side and end shakes look very good with just barely perceptible endshake and the same for the sideshake.
    Any advice would be appreciated, as I don't want to start tweaking things that should be left alone. I have serviced about half a dozen of these, so while I am familiar with them I don't have as much experience, especially with broken ones, as some of the folks here. I hope I'm using the proper terminology and have explained the situation well enough. Thanks in advance! George
     
  2. DeweyC

    DeweyC Registered User
    NAWCC Member

    Feb 5, 2007
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    Get Marvin Whitney's book. Sounds like the passing spring has worn down.

    Be aware almost all the detents are gone and they are now over $700 no matter who from, and mine are reserved for customer work. I bought my last ones from a Hamilton employee who took the needed equipment home and made them there. He has since died and I suspect the stuff went to the landfill.

    Almost as bad for escape wheels and my last ones were unplated (gold).

    A runaway M21 escapement can now result in $1200 of damage.

    So make sure you are certain what you are doing. Whitney covers it all but I still paid more than the cost of the book for my education.
     
  3. watchwldr940

    watchwldr940 Registered User
    NAWCC Member

    Nov 26, 2008
    396
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    18
    Thanks, Dewey. I elongated the hole and moved the passing spring out an almost an imperceptible amount. Since the escapement would move the locking jewel almost enough to unlock the escape wheel tooth, I didn't want to move it much, and it did the trick. I started out very cautiously only putting a small amount of power on the mainspring to check the action and safety and all is good. I've had it running for a few days now with no problems.
    I have Whitney's book and refer to it quite often. We're very fortunate that he shared his wealth of knowledge with us through his excellent book! George
     
  4. DeweyC

    DeweyC Registered User
    NAWCC Member

    Feb 5, 2007
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    I am glad I could help.
     

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