A few Pierce chronograph questions

jagrieff

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Jun 4, 2020
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I've been working on a lot of Pierce chronographs lately and I just encountered one that has a number of features that I had never seen before.
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First of all, the movement is marked 134 with the Pierce Pi logo.
IMG_3716.JPG
Then it has a real ratchet wheel click instead of the usual wire click. This version can actually be accessed from the train side of the movement so the dial does not need to be removed to let down the mainspring.
IMG_3820.JPG
The clutch disc is a rubber washer enclosed in a metal ring. Is this original or a later replacement?
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Finally, it is not marked with the letter M which I have seen on all other caliber 134 movements (By the way, what does the letter M stand for?). I assume that this is just a very late version of the Pierce 134 chronograph but I have worked on many and this is the first one that I have seen. Any thoughts?

Jeff Grieff
 

4thdimension

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Oct 18, 2001
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The clutch piece seems to be rubber (they’re bendy)and is part #X1740. I have sourced them at Otto Frei in Oakland but have heard of folks substituting a rubber crown gasket. Because these are flat on each side I think they could perhaps be made by slicing fine rubber tubing .-Cort

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jagrieff

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Jun 4, 2020
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I have restored a dozen or so Pierce chronographs and have used both rubber o-ring gaskets and washers made from vinyl sheets for clutch discs. Screen Shot 2022-05-17 at 1.34.40 PM.png
I have made a series of punches that I use to cut discs out of the vinyl sheets that are used to protect watches from scratching. I find that the vinyl discs work better than the o-rings as they tend to stay in place a little better. Whichever you use, the chronograph springs need to be readjusted to accommodate your new clutch disc.
Screen Shot 2022-05-17 at 1.34.24 PM.png Screen Shot 2022-05-17 at 1.34.31 PM.png
The clutch disc that I showed in my original post is quite different. I was surprised to see this washer completely enclosed in a metal ring securely attached to the chronograph arbor. All the others I have seen upon disassembly have been the hard crumbly remains of what was once a black rubber disc.

These chronographs are really an odd design but I feel that they are important because of their uniqueness.

Jeff Grieff
 
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