|The Little Engine that Could - Part
An indepth look at the ETA 2892
Here is the complete movement sans the balance wheel.
Picture 9 shows the balance wheel installed. The 9mm diameter balance is a good compromise between weight and size. Both the ETA 7750 and Rolex 3135 have approximately 10mm balances. In ETAís cheaper versions the balance is made of nickel. The ETA-Chron system makes centering the hairspring and adjusting the gap between the regulator pins very quick and easy. Unfortunately it also makes replacing the balance wheel complete quite a bit more difficult. The screw for fine regulation of the timekeeping, should not be used for more than a 5 second adjustment. Ideally it should be centered, as shown.
The dial side of the movement with stem, setting and winding system installed.
The complete dial side ready to be fitted with a dial. The large brass wheel at the 11 Oí clock position is the calendar driving wheel. The brass tooth peeking out from under the steel wheel cover, is the tooth that actually flips the date. This ingeniously simple design has been copied by many other manufacturers due to its simplicity, reliability and the fact that it gives a virtually instantaneous date change without needing extra parts. Itís also foolproof, such that one can change the time whether itís engaged or not without damaging anything.
The automatic winding train. The wheel second from the right is the reversing wheel. This wheel, together with the middle wheel, facilitates winding in both directions. The first wheel on the left is the intermediate reduction wheel. One can clearly see the jewel that replaced the stud. It sits on the small stud fitted at the top 12 Oí clock position of the automatic winding bridge.
Here is the auto winding unit complete, ready to be installed in the movement. With weight upside down one can clearly see the heavy weight riveted to its circumference.
Voila!! The complete movement ready to be installed in the watch case.
So what exactly is it that makes this movement so special? Or to rephrase the question, how come this movement is so accurate and reliable? Beats me if I know!! To be perfectly honest, I think that it is just a great design with compromises that have been intelligently chosen and superbly executed in its best incarnation. It incorporates all the latest knowledge and advances in both materials and movement design. Its generous supply of available torque means that it will not be easily stopped, even when powering extra complications.
If I was given carte blanche, what would I do to improve this movement?
Firstly, I would make all the bridges out of invar. This wouldnít do anything for its accuracy, and probably as much for its reliability. But as a watchmaker it distresses me to see high end movements made out of brass. Brass is just soÖÖ cheap. It also has a very poor coefficiency of expansion. Invar has a virtually zero coefficiency of expansion through a very wide temperature range. Itís also considerably stronger than brass. Being stainless obviously obviates the need to plate it too. How come Hamilton, Elgin et al produced zillions of inexpensive movements made of invar or similar alloys, but Rolex, JLC, Patek Phillippe etc make their very expensive movements out of cheap brass??
Secondly, I would do a complete redesign of the automatic winding unit to improve its efficiency even further. I would eliminate the reversing wheel and incorporate a JLC style switching rocker. And I would further reduce the diameter of the ball bearing oscillating weight support. Thatís one of the reasons for the Rolexís winding efficiency, the weight spins on a tiny diameter post. Unfortunately theyíve taken winding efficiency to the extreme. The net result is that said tiny diameter post doesnít offer enough support to the weight. This results in the weight scraping up against the movement bridges, even with mild shocks.
So how does it compare to the competition? There are some movements that match it in terms of accuracy and reliability, but in my humble opinion, none exceed it. The Rolex 3035 and 3135 match it toe to toe. But they are a lot thicker and considerably more expensive too. The PPs, while being very pretty to look at, do not match it for accuracy and are more delicate as far as reliability is concerned. Of course theyíre also slightly thinner, so that does put them at a disadvantage. The JLC 889/2 does match it for accuracy, but is also too delicate to give it any competition in the reliability department. The main reason for the latter is its very weak mainspring. The whole design, while being well thought out and superbly executed, relies too much on everything being just perfect. It is just thrown out of wack too easily, when even minor things go out of adjustment. I donít have too much experience on the Blancpain/Piguet movements. But from the few that have crossed my bench, they donít seem to deliver the same accuracy that the 2892 has no trouble delivering. Let me know if Iíve left any of your favorite movements out, and Iíll gladly comment on them.