Author Topic: Service: Omega Seamaster Chronograph ref. 145.0029 cal. 861  (Read 45 times)


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Service: Omega Seamaster Chronograph ref. 145.0029 cal. 861
« on: November 25, 2018, 11:29:12 PM »
Nice Omega watch came to service. Let's start the story from the cleaned parts.

Normally I would insert lowert shock assembly later, just before putting on the Balance, but because of the structure of this movement lower shock assembly was oiled and inserted at this point. Also assembly of keyless works is started.

Keyless and all connecting wheels in place. I follow service manual here, but I don't like this order of assembly as there is possibility of pinching cannon pinion teeth to the minute wheel while driving cannon pinion down later on.

Reason for the lower shock assembly. Support plate is added to the mainplate. Notice the hour recorder wheel and hour reset hammer. Yes - it's a chronograph.

Support plate or bridge to hold aforementioned in place. This order of assembly is needed as the barrel lower support is also this bridge.

New mainspring.

Barrel assembled. Hour recorder wheel driving wheel is attached directly below barrel. Always when chronograph is off, this wheel slips. Lubrication needs to be in order.

Here a view with the mainplate turned over. Hour recorder wheel easily visible.

Going train without escape wheel.

Barrel bridge gets assembled. Click..

.. and crown wheel.

Barrel bridge above going train. Escape wheel, escape wheel cock and pallet.


Initial readings looks good.

Now we can proceed to the chronograph parts. This is start-stop-mechanism. When fully assembled, "column wheel" alternates in two positions when start-stop pusher is pushed repeatedly.

Chronograph second wheel and minute register wheel and their connecting wheel.

Chronograph bridge. The minute recorder wheel click is integrated into this bridge.

Chronograph bridge in place.

Here the brake is installed. When is Stop-position, brake engages to chrono second wheel holding it still.
Notice also a small stick poking on the left side of the start-stop lever.

Chrono driving mechanism. In Start-position driving wheel engages to the chrono second wheel.

Hammer. Remember the small stick I just mentioned? When this stick is driven to side, hammer is freed resetting chronograph counters.

Lastly connecting rod to transform the state of the chronograph to the front side of the mainplate.

Back to the front side. The connecting rod is at 9 o'clock on the figure.

This mechanism prevents resetting hour recorder when the chrono mechanism is in start-position. Also this mechanism acts as a brake for the hour recorder wheel while in stop state. - Very clever.

This is the fine detail of this movement. In many cases the chronograph movements have 3 states: start, stop and reset. In this movement the column wheel has 2 states: start and stop and it toggles between these two. But if reset is pushed when chronograph is in stop state, hammers are enabled to reset the counters.

Dial and hands and final testing the movement operations.

Movement cased.

Finally the watch is in the hands of happy customer.