My Soviet chronometer clone is finally finished, and it’s timing beautifully.
I made sure to get the nicest one I could find, and it paid off at the timing machine. The 6-position delta is down to about 15 seconds, which is better than I ever expected for a 60-year-old Soviet wristwatch.
Assembly was a bit of a challenge, however, because of a curious design that Vostok used to drive the center seconds pinion.
Many vintage watches with indirectly-driven center seconds use a tension spring to keep the seconds hand from jumping around, as seen above. The drive wheel runs off the 3rd wheel pivot, and the center seconds pivot runs through the hollow center wheel arbor. Without the spring, the pinion is only under tension when the escapement is unlocked, and is loose during the balance wheel’s supplementary arcs. This translates to a seconds hand that “wiggles” as it circles the dial.
This Luzerne uses a coiled spring to keep radial tension on the pinion, which is an unusual implementation, but the idea is the same.
The Vostok uses a strange split wheel, which thoroughly confused me upon reassembly. My initial thought was that the upper wheel is designed to drive the 4th wheel pinion and the lower one drives the second pinion, but that doesn’t work at all. The upper 3rd wheel freewheels on the arbor, and will let the mainspring’s power out through the motion work if it’s not engaged with the lower wheel. The center seconds pinion is the bridge to lock those wheels together.
When the seconds pinion runs between the two wheels, the leaves of the pinion are constantly meshing on both sides with the two 3rd wheels. The lower wheel wants to release the mainspring’s power, and the upper wheel is stopped by the escapement. Together, the wheels provide opposite tensions, keeping the center seconds hand from jumping.
The original Zenith 135 didn’t have center seconds, so this is a completely Soviet innovation (from what I can tell). It’s a complicated but effective solution to the problem.
Because I’m a sucker for the look, I replaced the ugly short center seconds hand with a blued steel hand (which reaches properly to the minute track, of course). I think it adds considerably to the watch’s aesthetics!
Watchmaking student at the Lititz Watch Technicum, formerly a radio and TV newswriter in Chicago.