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