Chronograph cal. 31659

I already made a quick presentation about those soviet military chronographs (click to read). This one was bought in Moscow in 1991 or 1992 by its previous German owner, who wore it and stored it away when it stopped ticking. When it arrived on my desk, it looked good but was completely frozen. The movement is quite tough, it does have a shock protection device so what did go wrong? Balace staff OK, the chronograph did not block the watch, I had to dismantle all the chrono parts to find …

A toothless gear!

The ratchet wheel somehow lost 12 teeth, of course some of them found their way into the gear train and blocked the watch. A very uncommon mishap! The steel used to make the wheel may have been too hardened? Anyway, this is impossible to repair, so I had to find a replacement.

Let’s look at the insides of this chronograph; in particular, this a hacking version of the regular 3133, meaning that a lever stops the balance when the crown is pulled to adjust the hands:

What makes the 31659 a hacking 3133

Alongside a 0.6mm screwdriver for size:

A closer view of the hacking lever

Gear train and chronograph parts

The bare movement in a chronograph can be quite simple, this is the case : a 21600 bph watch, big diameter, small seconds. All good for simplicity and accuracy.

The bare movement

We can see from left to right : driving wheel and coupling clutch, chronograph bridge with seconds and minute counter, sliding gear and the command levers (start/stop and reset). Lots of screws, do not mistake a simple screw for an eccentric.

All chronograph parts minus the cam and reset hammer

Each function (seconds counting, minutes counting, resetting, coupling the chrono with the watch…) is triggered by the cam, which is itself rotated by the command levers (i.e. the pushers). The cam is just behind the reset hammers:

The heart of a cam-operated chronograph

More parts on the dial side!

The Soviets did not use a Western shockproof device, but designed their own. This one looks like an Incabloc from a distance, but the “lyre” has no hinges, it must be carefully (!!!) removed to access the jewels:

Soviet shockproof device, Incabloc-like but more difficult to handle

All is put back together, this one is now good to go:

Back together, and running

A late soviet-made 31659 ‘Sturmanskie’ military chronograph

Note: This chronograph does look like a Valjoux 7734, but it is different: small balance and higher bph, different jewel count, and I did not try to mix parts but I bet that most are not interchangeable. The Soviet obviously based their design on the 7734 but this is not a carbon copy!