1MChZ Caliber 2608: The Hunchback Central-Seconds Movement Explained

The Hunchback: Inside the 1MChZ Caliber 2608, a Central-Seconds Cousin of the Pobeda 2602

"And now — the hunchback! One arched bridge, and a movement that makes you take the whole watch apart to change a broken stem. Sturdy as a vault, and twice as much trouble to open."
— A bench watchmaker's aside

Soviet horology produced a long line of movements descended from the Pobeda 2602, and most of them are familiar territory for anyone who has serviced a few. The 2608 is the odd one out. Built by the First Moscow Watch Factory named for Kirov (1MChZ), it carries sixteen jewels and a center seconds hand, and it earns its workshop nickname — the "hunchback" — from a single, unmistakable feature: a high, arched going-train bridge that rises over the wheels like a vaulted roof. That arch dictates everything about how the movement is taken apart, and not in the watchmaker's favor.

This is the watch itself: a modest "Moskva" dial, sixteen jewels, 1MChZ of Kirov, with a sweep seconds hand.

Assembled Moskva wristwatch with a silvered dial reading 16 jewels and 1MChZ im. Kirov, fitted with a central seconds hand — The complete watch — a "Moskva" by the First Moscow Watch Factory, sixteen jewels, with the central seconds hand that sets the 2608 apart from the small-seconds 2602.

And here is the movement that lives inside it.

The bare 2608 movement removed from its case, seen from the bridge side — The caliber 2608 out of its case — the starting point for the teardown that follows.

The caliber's layout and markings read clearly here. The keyless works is of the older pattern: the intermediate setting lever, or yoke, is released by loosening a retaining screw rather than by a push button. The button comes later, on the "Sportivnye."

Close view of the 2608 showing factory markings and the old-style keyless works with a screw-released setting lever — Caliber markings and the early keyless works: this generation frees the stem by backing off a screw, not by pressing a release button.

From this angle the "hump" itself is in plain view — the raised going-train bridge. Someone, regrettably, has scratched it badly; hunting for gold, no doubt, where there was none to find.

The characteristic arched, raised going-train bridge of the 2608, its surface marred by scratches — The famous arch — the raised train bridge that gives the 2608 its hunchbacked profile, here disfigured by a previous owner's careless probing.

Opening the Movement

We begin without ceremony: remove the hands, lift the movement from the case, and take off the dial. The procedure asks for no special tricks — it is exactly as on the Pobeda 2602 or the Raketa 2603. The dial, or "slow," side of the main plate is likewise indistinguishable from the 2602.

Dial side of the 2608 main plate after removing dial and hands, visually identical to the Pobeda 2602 — The dial side of the plate — motion work and keyless works arranged just as on the 2602, with nothing yet to betray what waits on the other face.

The "fast" side, however, is a different animal, and so is the milling of the plate itself. We lift off the balance and the hunchbacked train bridge, and there it is: a new wheel arrangement. The first thing to strike you is the consequence of this design — to reach the mainspring motor, the entire going train must be dismantled, every wheel of it. Notice, too, how tall the wheel pivots are and how deeply the escape wheel is buried. Once again, no thought was spared for the ordinary watchmaker who must put a dozen of these right in a day. Want to replace a broken winding stem? Strip the watch entirely. On a 2602 or 2603 you need only lift the barrel bridge. But there is no use complaining — only noting the fact — so we press on.

Train side of the 2608 with balance and arched bridge removed, exposing the going train with unusually tall pivots and a deeply set escape wheel — The train side laid open: tall wheel pivots and a deeply recessed escape wheel mean the whole train must come out before the barrel can be touched.

Here is that celebrated curved train bridge on its own.

The removed arched going-train bridge of the 2608 seen from the top — The hunchbacked bridge removed — the arch raised the train just enough to clear the central seconds wheel running through the movement's heart.

And the same bridge from its underside.

Underside of the arched train bridge showing its jewel holes — The bridge from beneath, where its jewel holes carry the upper pivots of the elongated train wheels.

Now we take out the wheels — seconds, intermediate, and escape.

Removing the seconds, intermediate and escape wheels from the train side of the 2608 — Lifting out the going train: the center-seconds wheel, the intermediate wheel and the escape wheel, all with their conspicuously long arbors.

Only now do we gain access to the barrel bridge and the motor beneath it. A confession: I left the pallet fork in place, carried away by the work — shame on me, I might easily have broken it. But it survived. We take it out now.

The barrel bridge exposed with the pallet fork still fitted, about to be removed — The barrel bridge finally reachable. The pallet fork, nearly forgotten in the rush, comes out before anything else can be disturbed.

The train wheels, the bridge, the pallet fork and the balance now lie before us — the whole honest company. Is the balance worth dwelling on? It is the ordinary standard 2602 balance, without shock protection. That protection arrives in the next development, the "Sportivnye."

The 2608 going-train wheels, train bridge, pallet fork and an unprotected standard balance laid out together — The cast assembled: train wheels, bridge, pallet fork and the plain 2602-type balance — no shock setting, a feature still a generation away.

The Mainspring Motor

Now the mainspring motor can come apart.

We remove the ratchet (barrel) wheel.

Removing the ratchet wheel from the barrel arbor of the 2608 — The ratchet wheel lifted from the barrel arbor, freeing the bridge above the barrel.

Then — no, wait. While the barrel bridge is still in place and holding the center wheel captive, let us slip over to the slow side and pull the cannon pinion off the arbor of the center, or minute, wheel. As is proper in movements of this kind, it sits on a tight, biting friction fit.

Pulling the friction-fitted cannon pinion off the center-wheel arbor on the dial side — A detour to the dial side: with the center wheel still held by the bridge, the cannon pinion is drawn off its tight friction fit before the wheel can wander.

There. Now back to the bridge. Beneath the barrel bridge sit the barrel with its spring and the center wheel.

Under the barrel bridge of the 2608: the going barrel with mainspring and the center wheel — The barrel bridge lifted to reveal the barrel and the center wheel — the last major components still seated in the plate.

The construction of the barrel bridge deserves a word. There is no hard-alloy bushing for the barrel arbor, but there is a notably tall boss instead — the considerable height of the movement allows it — so the bridge is more than a millimeter thick at this point. A solid bearing. And see: zero wear. The plate is reinforced the same way. A strong, honest, well-made structure. There is also a jewel set under the heel of the center wheel — excellent — and although there is no counter-jewel in the plate, the body there is no less than a millimeter thick, so it is acceptable.

Close view of the barrel bridge showing a tall boss for the barrel arbor and a jewel under the center-wheel heel, with no visible wear — The barrel bridge: a tall, unworn boss carries the barrel arbor, and a jewel supports the center-wheel heel — height traded for durability.

The motor's parts are now before us.

The disassembled mainspring barrel components of the 2608 laid out — The going barrel broken down into its parts — barrel, lid, arbor and mainspring.

And so the watch is fully apart.

All components of the 2608 movement laid out after complete disassembly — The 2608 entirely stripped — every wheel, bridge and spring accounted for before cleaning.

I did not take the keyless works apart; I will simply show it assembled, since it differs in no way from that of the 2602, so a general view will do. The one thing to keep in mind is that the shaft of the intermediate-wheel jewel hides beneath the large setting wheel. That jewel must therefore be oiled before the keyless works is assembled, so it need not be taken apart again afterward.

The assembled keyless works of the 2608, identical to that of the Pobeda 2602 — The keyless works shown intact — a carbon copy of the 2602's. The jewel hidden under the large setting wheel must be lubricated first, or the assembly must be opened again.

The plate is worth a close look. I spoke earlier of the boss under the barrel arbor; now see how strongly the seat is reinforced — and not a trace of wear, like new. And this is 1956, mind you. Look, too, at the seat for the center wheel: as if straight from the factory. The designers did their work well. One more curiosity: notice the crescent-shaped recess milled into the plate. Here it serves no real purpose, but it was cut deliberately, with an eye to the future — to what? We will speak of the "Sportivnye" a little below, and it is there that this recess earns its keep.

Close-up of the 2608 main plate showing reinforced barrel and center-wheel seats and a crescent-shaped recess — The main plate in detail: heavily reinforced, wear-free bearing seats from 1956, and a crescent-shaped recess cut "for the future" — a provision the Sportivnye would later use.

Two words about the spring. Nothing remarkable: the ordinary standard 2602 barrel with a coiled spiral mainspring. No S-shaped springs were fitted to watches yet in those days.

The standard 2602-type going barrel of the 2608 with a conventional coiled spiral mainspring — The barrel and its plain spiral mainspring — the standard 2602 unit, predating the S-curve springs of later calibers.

Reassembly: The Motor First

So we have taken it apart, washed it, and made the acquaintance of a relatively little-known movement. Time to put it back together. With the keyless works already assembled, we go straight to the motor. We install the center wheel and the barrel. The wheel's arbor is oiled with MBP-12, and the barrel arbor with B-1.

Installing the center wheel and barrel into the 2608 main plate during reassembly — Reassembly begins at the motor: center wheel and barrel seated, the center arbor oiled with MBP-12 and the barrel arbor with B-1.

We prepare the barrel bridge for fitting. The center wheel's support jewel gets MBP-12, and a drop of B-1 goes into the barrel-arbor hole.

Lubricating the barrel bridge of the 2608 — the center-wheel jewel and the barrel-arbor hole — before fitting — The barrel bridge readied: the center-wheel jewel oiled with MBP-12, a single drop of B-1 in the barrel-arbor bearing.

We cover the barrel and service the crown wheel.

The barrel bridge fitted over the barrel of the 2608, with the crown wheel being serviced — The bridge set over the barrel; the crown wheel cleaned and lubricated as the winding side goes back together.

We clean the running track with pithwood and oil it with B-1…

Cleaning the crown-wheel running track with pithwood and applying B-1 oil on the 2608 — The crown-wheel running track pegged clean with pithwood and given a film of B-1.

…and assemble the unit. Note that there is no left-hand-thread screw here yet; two small screws secure the wheel.

The crown wheel of the 2608 fixed with two small screws, with no left-hand-thread screw — The winding wheel secured by two small screws — this early caliber has not yet adopted the left-hand-thread retaining screw of later movements.

Now we fit the cannon pinion. With that, the easy work is done. Next comes the train.

Refitting the cannon pinion to the center-wheel arbor of the 2608 — The cannon pinion pressed back onto the center arbor — the last simple step before the demanding job of the going train.

I can imagine the words watchmakers reserved for the designers of this caliber while assembling the wheel train. It took me nearly an hour. Just look at the length of the pivots and all becomes clear. On top of that, reaching the deeply buried escape wheel to guide it into place is no trivial task. Be that as it may, I got it together.

Reassembling the long-pivoted going train of the 2608 under the arched bridge — The train going back together — long pivots and a deeply set escape wheel made this the slowest part of the job, the better part of an hour.

And our caliber comes back to life.

The reassembled 2608 movement running again after service — Running once more: the 2608 ticking after cleaning, lubrication and reassembly.

The finish line.

The serviced 2608 movement complete at the end of reassembly — Done — the hunchback restored to working order, ready to go back into its case.

The Sportivnye and Its Stop-Seconds

And now, the promised short account of the 2609 movement — with central seconds and a shock-protected balance — found in the "Sportivnye," carrying a stop-seconds complication. This movement is built on the basis of the 2603 caliber: it has a shock-protected balance and an updated keyless works with a push-button stem release. Beyond that, a cap jewel was added to the escape wheel, raising the jewel count to seventeen. Here is that development before us, after repair. The work, besides routine servicing, included replacing the seconds-wheel jewel in the train bridge — something I have not yet described, so a fuller account of it follows below.

The 2609 Sportivnye movement with shock-protected balance, shown after repair — The Sportivnye's 2609 — a 2603-based, seventeen-jewel central-seconds movement with shock protection and stop-seconds, freshly serviced.

As I said, the caliber was refined relative to the one examined above. A cap jewel appeared on the escape wheel (green arrow), and the winding stem is released by pressing a button. But in the example that came to me the center-wheel jewel is missing. That, however, is fixable.

The 2609 showing a cap jewel on the escape wheel marked by a green arrow and a missing center-wheel jewel — The improvements: a cap jewel on the escape wheel (green arrow) and push-button stem release — but the center-wheel jewel is absent and must be replaced.

Re-Jeweling the Seconds Wheel

First we look for somewhere to take a jewel from. The jewels are the same as those used in the 2602 and 2603 calibers, and I keep faulty bridges from these calibers in my stores. The bridge is bent, but the jewels are sound. We will extract one. I have no press, so we use a wooden stick sharpened to the diameter of the jewel with a flat end, working it like a punch. We lay the bridge on a staking block and gently push the jewel out toward the inner side of the bridge.

Pushing a jewel out of a bent donor bridge with a flat-ended wooden pusher on a staking block — Harvesting a donor jewel: a bent 2602/2603 bridge on a staking block, the jewel eased out with a wooden pusher in place of a press.

Excellent. The jewel has come out of its setting. The main thing is not to overdo it and to work carefully.

The donor jewel successfully pressed out of its setting — The jewel free of the donor bridge, undamaged — patience rewarded.

Now the reverse procedure. The jewel must be set in place of the missing one, and with the wooden punch we send it into its seat.

Pressing the donor jewel into the empty seconds-wheel setting of the 2609 train bridge with a wooden punch — The salvaged jewel driven into the empty seconds-wheel setting of the Sportivnye's bridge, again by hand with the wooden punch.

It remains only to set the jewel to the correct height, so that it neither pinches the arbor nor leaves too large a gap between the jewel's face and the shoulder of the seconds wheel. Lacking a micrometer, we do this by eye, judging by how the pivot emerges from the jewel and by the freedom of the train. It worked!

Adjusting the height of the newly set seconds-wheel jewel by eye to control endshake — Setting the jewel's depth by eye — endshake judged by the pivot's emergence and the free run of the train, with no micrometer to hand.

The Captive Lyre Spring

The bridge can go back in place. Done! And one more thing. Remember I spoke of how the "lyre" — the shock-protection spring that retains the balance bouchon — is permanently fixed in these movements and is not lost during disassembly? Let us see how that is achieved in practice.

The repaired train bridge refitted to the 2609, with the balance shock setting in view — The re-jeweled bridge back in place. Attention now turns to the shock setting and its captive lyre spring.

To do so we take the bouchon setting out of the plate and examine it from the reverse side. There it is. See the special grooves machined into this part, into which the arms of the "lyre" engage. The spring is thus held securely and is not lost when the movement is taken apart. This assembly can be opened as often as you like with no fear of losing the little spring. How sorely this is missed in the Raketa 2609.NA!

The underside of the balance bouchon setting showing grooves that capture the arms of the lyre spring — The bouchon setting from behind: grooves capture the lyre spring's arms so the shock spring stays put through any number of disassemblies — a refinement the Raketa 2609.NA lacks.

The Stop-Seconds Mechanism

"And now…" — no, no, not the hunchback this time — now, the stop-seconds! This is how the movement's hacking device is built. Two parts have been added: a stop lever with a spring finger, and a flat spring for that stop lever. The lever is controlled by the tail of the winding stem. When the stem is in the winding position, its tail emerges from its seat and presses on the heel of the stop lever, and the spring finger pulls away from the balance wheel, allowing the balance to run. When the stem is moved to the time-setting position, the tail withdraws into its tunnel, freeing the stop lever, which under its flat spring shifts toward the balance and presses the spring finger against the balance wheel, arresting it. The balance stops, the watch stops. Returning the stem to its normal position swings the lever back, drawing the finger away, and the watch runs again.

The added stop-seconds parts on the 2609: a stop lever with a spring finger and its flat actuating spring — The hacking assembly: a stop lever with a spring finger and a flat spring, driven by the tail of the winding stem to brake or free the balance.

Let us watch it happen. In the picture the movement is in the running state. The winding stem is in the winding position. We can see the spring finger, the lever's flat spring, and the stem's tail emerged from its tunnel, bearing against the heel of the stop lever.

The 2609 in running state: stem in winding position, its tail pressing the heel of the stop lever to hold the spring finger clear of the balance — Running state: with the stem pushed in, its tail presses the stop-lever heel, holding the spring finger away from the balance.

This picture shows clearly that, with the stem and stop lever in this position, the balance is not braked and is free to run.

Detail showing the spring finger held clear of the balance wheel so the balance can oscillate freely — The spring finger standing clear of the balance rim — the train is free and the watch keeps time.

For clarity, the mechanism from another angle.

Alternative view of the 2609 stop-seconds mechanism in the running position — The same running position from a different viewpoint, showing the geometry of lever, spring and stem tail.

Now we move the winding stem into the hand-setting position and pull it out. As we see, the stem's tail has retreated into its tunnel, and the stop lever has carried the spring finger toward the balance.

The 2609 stem pulled to setting position: the tail withdraws into its tunnel and the stop lever moves the finger toward the balance — Stem pulled out for setting: the tail vanishes into its tunnel, releasing the stop lever, which advances the finger toward the balance.

And here we see plainly that, in this position, the finger touches the balance wheel, brakes the balance, and stops the watch.

The spring finger contacting the balance wheel, stopping the balance and the watch — Contact made: the spring finger rests against the balance wheel, halting it — the hands can now be set against a stopped seconds hand.

And from another angle.

Alternative view of the 2609 stop-seconds engaged, finger braking the balance — The braking action from a second viewpoint, confirming how lightly the finger need bear on the balance to arrest it.

An interesting complication, then. In all honesty, to my mind it is a fairly debatable one. The central idea was to let the watch be used as a stopwatch and to make it possible to synchronize several identical watches together. The caliber turned out reliable enough, but not especially convenient to work on. If I am not mistaken — and correct me if I am — it was this mechanism, in the "Shturmanskie," that Gagarin took into space. And successfully. Yet the movement's excessive height and its wholly unprotected wheel train left no room for further development of the design. On the other hand, as we can see, these calibers remain repairable and keep working to this day. And one last thing — let me show the keyless works, so the complete analogy with the 2603 caliber is plain to see.

The assembled keyless works of the Sportivnye 2609, identical in layout to the Raketa-related 2603 caliber — The Sportivnye's keyless works — laid out exactly as in the 2603, closing the family circle that began with the humble hunchbacked 2608.