Zenith 1731

 
Zenith 1731

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.

base plate

base plate

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.

gear train

gear train

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.

side view of the gear train

side view of the gear train

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.

barrel bridge

barrel bridge

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.

Zenith 1731: Dial side

Zenith 1731: Dial side

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

Manufacturer:Zenith
Caliber:1731
Size:7 3/4''' (measured: 17,3mm)
Height:2,70mm
A/h:21600
Number of jewels:19
Escapement:Pallet lever
Balance types: Glucydur anular balance (three legs)
Shock protection(s): Incabloc
Balance bearing / direction hairspring:Clockwise
Moveable stud:yes
Adjust mechanism:unknown
Construction:
  • lever
  • escape wheel, transmission wheel, seconds wheel, third wheel
  • center minute wheel, mainspring barrel
Construction type:solid construction
Winding mechanism:yoke winding system
Setting lever spring:4 hole(s)
Features:
  • s (decentral seconds)
Production years:1967-1969
Production figures:15000 (1730 & 1731)
Inventory number:21036

Usage gallery

Zenith ladies' watch (case missing)

Zenith ladies' watch (case missing)

This movement is a kind donation from Philipp Porter to the movement archive. Thank you very much for your great support!

Other movements from Zenith