Longines Calibre 12.68Z model 7033-4 – Service and restoration

Nick sent me this vintage Longines watch for a service and restoration. I have already featured an almost identical watch on the blog in this article. The service on that particular watch had been perfectly straightforward, but in the case of Nick’s watch it turned out to be a little more complicated as you are about to find out….

Vintage Longines Restoration

I start by removing the caseback, which exposes the beautiful Longines calibre 12.68Z.

 

 

The hands are carefully lifted after removal of the bezel and crystal.  The dial has severe signs of ageing, and Nick asked me to arrange a full restoration of the dial.

 

 

 

I start stripping down the dial side, it is pretty straightforward, with no date complication to worry about.

 

I then move on to the upper side of the movement. After removal of the ratchet wheel, I can immediately see that not all is well with this movement: there is excessive wear on the barrel bridge hole, and, as a result, the barrel has too much sideshake.

 

 

The hole in the barrel plate has worn out of centre, which makes the barrel tilted when the watch is running.

 

 

Not good for power delivery, and eventually this can lead to the barrel binding with the centre wheel.

On the close up shot here you can see a significant gap between the barrel arbour and the bridge. It may not look like much, but this is very significant in the context of horology.

 

I will have to rectify this but for now I proceed with the strip down, and ultrasonic cleaning of the parts in the cleaning machine.Longines 12.68Z service

 

Unfortunately, a replacement barrel bridge is not available, this part is the Achilles’ heel of this movement and I expect supply has long dried out. In order to remedy this I will have to re-bush the bridge, not the easiest job as the plate is very thin indeed (0.4mm around the hole).

 

 

 

I first bring the hole back to its original centre by manually broaching the hole. I then enlarge the hole with a reamer to accommodate the bushing.

 

 

 

 

 

The bushing is pressed in place, it is essential to have the correct amount of friction here: not too much or the plate will be damaged, and not too little or the bushing will be loose.

 

 

 

 

I then manually broach the bushing, this time to open the hole to the correct diameter to accommodate the barrel arbour.

 

 

 

 

I finish by making a chamfer on the new bushing, and, after cleaning the bridge, it is now ready for assembly.Watchmaking rebushing

 

The rest of the assembly is straightforward, and I do not encounter any issues.

 

Once the movement is fully re-assembled, I check its performance on the timegrapher. The rate is nice and stable, and the amplitude is excellent, but I was a little disappointed by the positional error, on the high side for this movement. I therefore decided to dynamically poise the balance, using the timegrapher to identify the heavy spot and rectify it. Very much like one would do to balance a wheel on a car, but on a much smaller scale.Balance wheel poising

 

A small timing washer was added to the opposite side of the heavy spot of the balance, and the positional error was much improved as a result.Timing Washer

 

The calibre 12.68Z is a real joy to work on, and I wanted to point out a few details which in my eyes make it a very attractive movement indeed…

 

This is the underside of the ratchet wheel, with a beautiful finish, which cannot be seen when the movement is assembled, a real treat for the watchmaker!

 

 

This is a close up photo of the train bridge, you can see the beautifully brushed finish on the plate, and also note that that jewels are set in “chatons”, settings you only find on high end watches nowadays.

 

 

 

Meanwhile, I received this back from the dial restoration specialist, who has done a fantastic job.

 

 

 

 

Dial and hands are fitted back onto the movement, which is re-cased. The final touch is a brand new Italian leather strap. The watch is completely transformed, and looks fantastic.Longines-7033-4-service

I would like to conclude this article by thanking the owner of the watch, Nick, for entrusting me with this very interesting restoration project, and allowing me to feature it on the blog.

 

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