It depends on the movement. The 2836 in all of the non-chrono watches, including the the 2893-2 found in the MBIII are bidirectional. The Valijoux 7750 series found in the non in-house chronographs are unidirectional.Originally Posted by chunkythebulldog
J.
To be more precise the 7750 rotor will spin bidirectionally, but the mechanism that transfers that into charging the mainspring is unidirectional. What's really amazing about the 7750 movement is that the original movement on which it's based was a manual winding chronograph known as the Venus Calibre 188 and dates from 1948.
Unidirectional mechanisms tend to spin at higher RPMs than bidirectional ones because if energy is imparted in the non-winding direction it faces almost no resistance. This then leads to Rotor Wobble on the wrist, where you can actually feel the rotor spinning as it's an inherently unbalanced motion. I take it that this is then the grinding noise that the OP refers to?
It's also that the 7750 rotor has considerably more mass than the rotor in the 2836 type movements, and will spin more easily in either direction, however you're right that it's easier in the non winding direction and the wobble is the result. The 2836 also has 2 reversing wheels in the automatic bridge, which engage with the geared teeth of the rotor, and these are both clutch wheels so damp the rotation of the rotor. The 7750 only has a single reversing wheel/clutch so has far less resistance to the greater mass of it's rotor! If anyone is interested you can download the parts lists and servicing diagrams from ETA here by selecting either Mecaline or Mecaline Specialities and then clicking the calibre number in the next drop down box.
https://secure.eta.ch/CSP/DefaultDes...dex=1&tabid=28
Agree, the chronographs have a little bit of "wobble" as you wear them and you can hear it if you listen closely.
Last edited by kaufen; 09-21-2016 at 09:11 AM.
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