Repair, Restoration, Omega Military cal 283

Repair and Servicing of Omega Military Cal 283

The owner said that the watch was not keeping accurate time and that it would start and stop running. So it was sent in for diagnosis and repair of the defect, along with a full servicing.

Here is an overall view when it arrived





With the caseback removed, if you look closely, you can spot a defect



A closer view of the balance cock and balance reveals one of the problems, the hairspring is bent and damaged





Overall the movement is in poor condition, it's very dirty and gummed up with old oil, the sweep seconds wheel was bent and touching the bottom of the sweep seconds pinion cock, and there was surface rust in the keyless.









The movement was completely disassembled, here is an overall view of the movement in pieces ready for the cleaning.



Hairspring defect

So why was the hairspring bent and distorted? The damage certainly didn't happen on it's own, someone carried out the rate adjustment and didn't pay attention to the regulator and the effect that the regulator was having on the hairspring.

A close look at the regulator pins shows that they are not positioned properly, the pins should be perfectly parallel with each other with a small gap each side of the hairspring. As shown below, the pins are too close together, and tapered, which doesn't allow the hairspring to breath properly. When the regulator was moved, instead of the pins sliding along the hairspring surface, the regulator pins grabbed hold of the spring and the spring was bent.

Here is a close up view of the regulator pins, see how they are tapered and too close together, as well as being very dirty, you can see how the pins would grab hold of the hairspring.

BEFORE


After cleaning in the ultrasonic machine, I fixed the pins and here is what they should look like, now the hairspring can breath properly and slide between the pins as the regulator is adjusted.

AFTER


Here is a closer look at the hairspring once the balance was removed from the cock, this is before repair.



This type of defect is repairable, however there is always a risk with a bend near the stud that the spring will break during manipulation, but that is a risk you have to take. If during manipulation the hairspring was broken from the stud, I would remove the taper pin from the stud, reinsert the spring end, and secure it once again with the taper pin.

Some careful manipulation with tweezers takes care of the defect, here's the result with it installed. It now follows the arc path of the regulator arm and no longer grabs the spring when adjusted.



After the ultrasonic bath, rinses, and drying, the parts came out nice and clean.

Here is the sweep seconds wheel and pinion, cleaned, oiled, and with the wheel installed level with the bridge.



Keyless looks much better.





After assembly and oiling, a slight adjustment of the beat was needed, which has to be done by removing the balance from the balance cock, then you move the hairspring collet on the balance staff in the right direction, reassemble the work, and put on the analyzer to see if you got it right. As well; the hairspring needed a slight adjustment in the flat, and the rate adjusted on the analyzer. I timed and adjusted the movement in all 5 positions, and the movement ran well within specifications.

Thank you for reading.

BHI Professional Watchmaker, www.roberthoran.eu

Wonderful job and results 👍

Nice work, great pictures, thanks.

Glad you enjoy the post.

If the spring was shorter, the rate would increase, but the change could easily be compensated for by adjusting the regulator to a slower position.

Interestingly the hair spring was somewhat long and probably a replacement, this due to the fact that I had to adjust the regulator to the max Fast position to have an acceptable rate on the analyzer. In this case, a shorter spring would be a good thing, because it would move the regulator from the max Fast position to a more midrange one, where you would prefer it to be.

Great question, thanks.

Love these posts! Very interesting! Thanks for taking the time to do it, for learning and amusement! 👍

Wouldn't it be possible to remove or add weight to the balance to change the rate to keep the regulator more to the mid-range. Or is this method just a really colossal PITA?

Very interesting Rob and neat work with that hairspring and regulator. I can appreciate how critical these adjustments are to getting the movement to run well in all positions and it's not as easy as you make it sound.😉

I've just completed a 1951ish cal 351 which also needed hairspring work (not as much as this though) and was very dirty with some other problems. Running well now but these 50s movements seem to be more abused than ones just a decade younger. Are you also seeing that or have I just been unlucky so far....

Out of interest, do you usually remove the balance and hairspring from the cock before cleaning or was it just this movement? I've been cleaning the plate with the balance/cock installed and Incablocs removed. Any adjustments being done afterwards. Just interested to see if there is another way of doing it.

Cheers, Chris

I do have boxes of timing washers, vintage ones because they don't seem to be manufactured anymore (probably due to modern balances not having any timing screws). Because I was able to get the rate where I wanted it with the regulator, I choose not to add washers. If you do add washers you really need to poise the balance to make sure it's not been affected with the addition of the washers. Not a total PITA but certainly a lot more work, but if needed, it can be done.


Chris, as a standard practice I only use the ultrasonic on the balance/hairspring if it's very dirty, and if I do use the ultrasonic, as a final rinse I always use one-dip hairspring cleaner.

If the hairspring and balance look clean, I soak them as a unit in hairspring cleaner, give the pivots and roller a scrub with a fine paint brush, then dry in sawdust and blow clean with the bellow.

I find that no matter how clean or new the ultrasonic rinses are, they always seem to leave a residue on the hairspring that causes it to cling together, and that I end up having to clean off with hairspring cleaner anyway.

Hairspring adjustments are as you say are not so easy and time cosuming, a big help is a good quality articulated binocular microscope, which I have on the bench for detailed work, especially on the lathe and hairsprings.

I would never consider replacing a complete balance assembly when the hairspring is distorted or simply broken/unglued from the stud, some repairs can take extra time, but I don't want to get lazy and become a parts changer, I prefer to challenge myself and keep my skills honed.

Rob