Service: Omega Speedmaster calibre 321

IMG_1945Richard sent me this lovely Speedmaster, as he wants the central second hand changed. No problem, as he also supplied the new hand!A common problem with the 321 is banking, e.g. the mainspring is so strong that the amplitude of the balance gets too high, making the impulse pin hit the back of the pallet fork as it swings around too far.IMG_1902

And so it is with this one. I fully wind it, and put it on the timegrapher. After a few seconds, the movement starts banking. Note that I haven’t adjusted the lift angle to 40 degrees yet, but that doesn’t matter. It’s the straight line pattern suddenly becoming a random set of dots that shows that the movement is banking.IMG_1947

Funnily enough, my friend Al from sent me an email the day before pointing out to me that these movements often bank! That’s what you call coincidence …IMG_1984There is only one way to change the mainspring, and that is to take apart the movement…IMG_2192

With Al’s help, I decide on a 1.30 x 0.105 x 420 x 11 mainspring. This is longer than the original one, so it gives more power reserve, but also thinner to prevent banking.IMG_2194

I start off with the base movement.IMG_2197

I still have to set the timegrapher to 40 degrees lift angle, so ignore the amplitude, but I first have to attend to the high beat error.IMG_2217

That looks better – and the timegrapher now shows the correct lift angle.IMG_2201

Putting a chronograph movement back together is a slow process. Every part has to be properly lubricated and its movement tested.IMG_2204

And here we are with the chronograph back together.IMG_2205

The bottom plate holds the slightly unusual hour recorder construction. The hour recorder is constantly driven by the barrel, but a brake prevents it from turning. When the chronograph is started, the brake moves away, and the hour recorder is turned by the barrel.IMG_2207

The new central second hand is back on. There are still some specs of dust on the dial, and I blow that off with a small air gun attached to a compressor – I got one that is used for spray painting model airplanes, and it’s great for blowing dust out of cases and off dials.IMG_2218

And back together.

4 thoughts on “Service: Omega Speedmaster calibre 321

  1. I’d wish Christian would stop posting these 321 Speedies! I want one too!! 😉
    Fantastic watches and a very clean example. Cool!

  2. I cant see any difference between the old and new second hand… its the same, just new?

    Something classically stylish about the design of the Speedy – nothing about it seems extraneous 😉

    • It looks like it had the later flat-ended one and it’s been replaced by a more correct teardrop ended one.

      There seems to be some debate about what’s really correct for later 145.012s as Omega fitted the new hands as they used up old cases/movements and the later hand was used as a service replacement. Apparently many of the Omega Museum watches have ‘incorrect’ hands.

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