Zenith 1731

Description

A really rare movement is the, between 1967 and 1969 in a quantity of only 15.000 items produced Zenith 1731, which even has to share that number with its direct relative, the base caliber Zenith 1730.

This windup movement for ladies watches measures only 17.3 mm in diameter (7 3/4 lignes) and is not found in any of the well known movement finders.

The base plate already shows the high quality of this movement; even the minute wheel is ruby-beared here.

The second thing, that stands out is, that the gear train has got an additional wheel, since normally, between the escape wheel and the center minute wheel (when used) are only two reduction wheels.

The mainspring barrel drives the center minute wheel, followed by third wheel and seconds wheel. So far, nothing special. But now, instead of the expected escape wheel, there’s another reduction wheel, which is not only low toothed, as the seconds wheel, but is also massively made. Only now follows the filigree steel escape wheel, which is mirrored due to the additional wheel.

The reason for this construction is now really known, but you can speculate, that it might be used because the low toothings and the second reduction step might allow a better force transportation to the escape wheel and thus a higher precision.

The regulating organ of the Zenith 1731 belongs the best ones available at that time. It consists of a screw-less three leg Glucydur balance, which is beared in two Incabloc shock protections. It beats already with 21600 A/h and can be regulated with a toothed fine regulation.

Of course, as escapement, a swiss pallet lever escapement is used.

An interesting detail is the ratchet, which is only a spring, screwed into the barrel bridge. Although it is optimally secured against flying away, this construction is a bit too simple for the otherweise so very well made movement.

The dial side is pretty standard with the yoke keyless words and the Incabloc shock protection, you can see there.

The slanted edges were required to make the movement a bit more flat on the outer edges for the use in extra flat watches. With a height of only 2.7 mm, this movement is really very flat.

Technical data

Usage gallery