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Landeron 51 Chronograph disassembly


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In preparation for the repair of my own chronograph, I found this one amongst the watch graveyard and decided to take it down and put it back together.  These are the photos of the disassembly.  After disassembly, I put forth an effort to clean the parts with Ronsonol.  I was not passionate about the clean because the purpose was to validate both disassembly and reassembly.  I am happy to say that everything went off without a hitch.  I even removed the mainspring and found the appropriate mainspring winder among my dad's tools.  No problem.  The hairspring was quite gnarly due to the watch's misadventures among others in the scrapyard!  I did my best to straighten it.  It tic'ed a few strokes when I realized that it was way out of beat.  So, after watching some videos, I rotated the hairspring  until it was close.  It tic'ed a little more, but the hairspring was just not playing along.  That is OK, I accomplished the goal of tear down and rebuild, and I also got to experiment with hairspring adjustments.  No springs, and no screws were lost!!one.png.c06c228e2f93ae66aeca208caf416a11.pngtwo.png.5fb2636194f6d678852ce95e2190f6ba.pngthree.png.ce32e5a559e090afb4845b92ab88d718.pngfour.png.1fa0adb44d51e717335c26e3ec52d438.pngfive.png.d64d5a8bb37d90396d61faf26f3f2fbf.pngsix.png.be34b6e78163ea53330f7fe4e60e7d2d.pngseven.png.18f51c6ea816412fc88fa9e6b7040ac4.pngeight.png.8c3e3ce69293c99e7d995f208eb81be2.pngten.png.624ccbfa26b255aa9be86f4676d90367.pngeleven.png.43a45be94ad4d2b263ba5998705821da.pngtwelve.png.074a2f83a044adf5a6f86a1bf798411c.png

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  • 3 weeks later...

I decided to dedicate some money to a complete restore.  Found a balance complete for a 248 on ebay and purchased it.  Ranfft indicates the 248 is derived from the 48 as is the 51 which I have.  Many parts interchangeable.  We will see.  Next up will be to find a suitable dial and hands.  Seen a few on ebay.  I have a dial, so maybe have it restored...¯\_(ツ)_/¯

Stay tuned!!

As noted originally, this is in part to continue to hone my skills before attacking my Valjoux.

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    • That's a good idea - shrinking down the nut and wrench size from the old casebook trick!
    • I missed this earlier. The dial isn't going into the holder, it should sit proud of it. This is what I am currently using which I print for each different movement.    
    • I didn't think pulling to set position would work harden the spring, in that position it is stressed where the arm starts. By work hardening i meant rapid polishing at that point, a bit like polishing a pivot work hardens as it compresses the steel. I doubt polishing by hand would achieve much in that respect though. Its finished, arm polished up mostly at the join to the bridge's main body. I'm ok with it, the screw holes aren't great as i had to open them up by redrilling and positioning it was difficult, I'm not much use with a loupe, opening up with a file might be a better option for me or i could just use the correct drill size 😅. And the detent is way too deep, i had to guess that with the stem release out of position and sat on top, but i only took one measure and went for it, no slowly slowly catch your monkey 😅. First go I'm happy , well sort of, it works and thats a big thing for me, next one will have a bit more finesse.  Anyone thats interested, after filing, i used a 2000 grade home made diamond  micro file and then 20 micron film, the film is much better than wet and dry, more stable to use and doesn't shed cheap grade grit everywhere , then auto polish on a sponge pad.
    • I'm assuming that every time you set the watch you are work hardening the detent spring, maximum hardening is  where it meets the plate due to maximum deflection.   That's why it snaps there.  The Young's modulus may be the same but after it's reached its maximum yeid strength it breaks.  My mechanic engineering is very rusty, correct me if I'm wrong. 
    • Ah ok yes that makes sense to polish it where the arm starts to form from the body of the bridge, i thought you meant the underneath of all the arm.
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