Chronometry: Model 21 mystery part?

Discussion in 'Chronometers' started by MrRoundel, Jun 27, 2019.

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  1. MrRoundel

    MrRoundel Registered User
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    Dec 28, 2010
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    OK, so maybe it's just me. I was finally getting to the point where I was installing the balance in my Model 21 chronometer. Then, in with the screws for the HS stud, I found a silver colored bushing (spacer). I thought, hmmm..., where does this go? In the screw recess in the balance cock? No. Hmm...I guess I'd better check the parts list.

    So far I don't see it anywhere. At first I thought it might be the fusee or barrel bushing, but the realized that those were the brass bushings in the upper plate. Can someone give me a clue on where it goes? It fits well inside the balance-cock screw recess, as if it was a spacer, but the screw doesn't seem to pass through all the way, and it would probably cause the screw head to sit too high. Hints? Answers? Help? Thanks.

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  2. MrRoundel

    MrRoundel Registered User
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    Dec 28, 2010
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    Mystery solved. I went to Bunn Spl's tear-down video and saw that it's a spacer that goes under the outside of the balance-stop arm that was only on the early Model 21s. Fortunately, the one he shows in his video has the balance-stop setup, and I saw the part. I don't believe the book mentions the balance-stop arm at all. Cheers.
     

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