Omega Seamaster Automatic Calibre 752 Service

This lovely vintage Omega Seamaster came in need of a service. The watch was not running very well.

It is powered by Omega’s Calibre 752. The serial number dates the production of this watch to 1968, it looks well preserved in appearance.

Omega-Seamaster-Automatic-Calibre-752-Service

I start by opening the case. This uncovers Omega’s Calibre 752, with the typical copper plating found on Omegas of the era.

Note the many finger prints on the rotor (not mine!), we are about to put this right.

The automatic works is removed from the movement. It will be stripped, particular attention will be paid to the reversing gear as the cleaning and oiling procedure on these is very specific and differs from conventional reversing gears.

The movement is taken out of the case. There are signs of ageing on the hand, but we should be able to improve this. The dial has very small marks, but all in all it is in reasonably good condition given it is half a century old.

Hands, dial and stem are disassembled.

This particular model has a 9ct solid gold case and case back. Thankfully the value of vintage Omegas nowadays is such that they no longer face the threat of being scrapped for gold rather than being taken care of  (unfortunately it does happen, if you ever wondered why there were so many loose movements sold on ebay).

At the time of writing, this is worth approximately £320 in scrap value (in excess of $400), it is easy to see why so many gold watches do not make it through the years. A crime against horology if you ask me!

 

 

I now move on to the other side of the movement.

After removal of the day indicator disc, I take out the date indicator guard.

 

This exposes the motion work. 

And now we are left with the keyless work, cannon pinion and minute wheel.

After disassembly of the above I move on to the other side of the movement.

This is a close up of the friction spring for the sweep second pinion. This design is typical of the omega caliber 55X, 56X and 75X  family of movements. I believe the rational for this design is to reduce the overall height of the movement. It is not unique to Omega, Rolex ( amongst others) also used it in some of their movements.

I proceed with the disassembly of the ratchet wheel and crown wheel, leaving just the barrel bridge, train and the escapement.

 

 

And finally the movement fully stripped, ready for cleaning.Omega-Calibre-752-Service

The strip down of the watch was straightforward, with the exception of a broken incabloc spring, more on that later.

The parts in the basket have been ultrasonically cleaned, those finger prints are gone!

 

Now is the time to address the snag I mentioned above. During disassembly, as I released the lower cap jewel spring to remove the jewel for cleaning, the spring split:

 

 

 

 

Close up of the broken spring.

 

 

 

This meant sourcing a new one, but replacing it is not so straightforward. The incabloc setting needs to be lowered ever so slightly to expose the hinges of the spring. It must be done with a jewelling tool, as extreme precision is required here (of the order of a hundredth of a millimetre). This is because the distance between the two end cap jewels determines the end shake on the balance wheel, the play, for want of a better word. Too little and the balance will be restricted and will lack amplitude, and too much is equally problematic.

 

 

The replacement spring.

 

 

 

And here in action, adjusting the height of the incabloc setting to have the correct end shake on the balance wheel (notice the micrometer near the top of the tool which allows the required level of control and accuracy to be achieved).

A few iterations were required to get the endshake just right. With this issue resolved, I completed the assembly of the escapement.

I start re-assembly with the mainspring. 

I then rebuild the train and winding mechanism and escapement.

 

       

At this stage, with the balance installed and everything in place for the movement to run, I like to test how the movement is performing on the timegrapher before proceeding with further assembly.

In this instance it was obvious that something was not right, there was a very irregular wave pattern (timekeeping varying at regular intervals).  I trace the root cause of the issue back to the third wheel which was out of true. Unfortunately this meant another interruption in the project, while a replacement was sourced.

After the receipt of the new wheel, the assembly was completed and I am pleased to say that at this point I did not encounter any further issues.

Prior to fitting the hands, I gave them a light polish to remove some of the marks and scratches. My intention here was not to make them look as new, but a bit more presentable, new hands would look odd on a old watch, I find it best to keep consistent patina across dial and hands.

And now with the dial, minute and hour hands fitted.

 

It is worth pointing out that on this movement, due to the design of the indirectly driven sweep second I mentioned earlier, the sweep second pinion needs to be supported when the seconds hand is fitted. Ideally this would be done with a specific movement holder, but in absence of this I used my staking tool successfully to press the seconds hand on the pinion arbor whilst supporting it from the other side.

I also polished the crystal, I first use wet and dry paper and then finish off with some polishing compound.

And the final touch was a very light polish with a soft cotton wheel on the case. Polishing is typically done in several stages. In this case I only used the final finishing compound, just to take off the natural tarnishing of the gold. The case now looks fantastic.Vintage-Omega-Seamaster-Automatic-Service.

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