Repair: Heuer Autavia / Buren 12

IMG_0476Andrew sent us this Heuer Autavia, and it’s running way too fast – about 5 minutes per hour. Usually, this happens if the hairspring is too short, e.g. two windings stick together, or it’s touching somewhere…IMG_0484

And, indeed, it does 60 seconds in 55 seconds!IMG_0475

The Buren 12 movement. It’s the first automatic chronograph movement, with a micro rotor beneath the chronograph layer. Not a movement that is entirely unproblematic, with several weaknesses.0423141533

First of all, I notice dirt on the hairspring. This watch was sold to Andrew by a dealer in the US as freshly serviced…0423143111Also, the hairspring is a bit deformed – see the last bit of the outermost coil towards the stud.0424092713

I start off by re-shaping the hairspring and cleaning it – this looks better.IMG_9916

The movement doesn’t look that well serviced, so I just take off the complete chronograph layer, and take the base movement apart. IMG_9950

The worst of the weak points of this movement – the intermediate setting wheel wears the plate down, and will then start to slip. This happens when the clutch is too tight, so too much force is needed to set the movement.Β 0427132456The damage to the plate under the microscope, with the intermediate wheel in place. This is all too common, and the reason why I don’t have a Buren 12 in my collection.IMG_9944The movement almost taken apart.IMG_9954

All the base movement parts go into the cleaning machine.IMG_9964

When putting the mainspring back in, I notice that the bridle has broken off the end – the mainspring will just slip in the barrel, without being able to build up a decent power reserve. These mainsprings aren’t available for love nor money, so I order a manual mainspring, and fit it with an adaptor bridle from manual to automatic.IMG_9993

The new manual mainspring fitted with an automatic adaptor bridle.0427104351I’m nowhere near being able to put this movement back together, though. I notice that both pivots have broken off the auto winder click – somebody had just “thrown” it into its place, without it being able to function at all. Nice job.IMG_9999

The new pivot needed isn’t exactly big, with the pivot ends 0.1mm thick, and the whole pivot only 0.4mm thick…IMG_9998A photo of the broken pivot on my index finger, just to put things into perspective!0427125544

Time to fire up the lathe, and to turn a new pivot. Here it is pressed into the click. I still have to size the right end, which I have turned a bit too long just to be on the safe side.0427130339But my problems aren’t over yet – the click itself has a worn tip, and it won’t engage properly with the wheel, so it can still turn freely in both directions.0427131510I take the click out again, and re-shape the tip so it will stop the wheel properly.IMG_0485

Having put the movement back together, it’s looking good on the timegrapher, but it’s still 5 seconds per minute fast! Time for some serious head scratching. I can exclude the balance and hairspring from the troubleshooting, as the beat rate is correct for this movement (21,600 b.p.h.), and my timegrapher shows me -6s/day, not +5s/minute. So the problem has to be somewhere in the gear train.IMG_0486This movement doesn’t have a centre wheel that’s in the centre, but it’s off-side, with the clutch on the centre wheel, and an intermediate wheel that drives the cannon pinion, which isn’t a clutch. (intermediate wheel second from left, centre wheel third from the left). Time to count teeth! The best way to do this is to take a high-res photo, and to count the teeth on the screen. What I get is this:

Escape wheel: 15/6
Fourth wheel: 66/8
Third wheel: 60/9
Centre wheel: 72
That gives me 1.0909 turns of the centre wheel per hour if the movement beats at 21,600 b.p.h.! The centre wheel has to course to turn once an hour, not 1.09 times. So the gear ration of one of the wheels is wrong. Armed with a calculator, I play with the gear ratios, until I find the culprit. Β The fourth wheel should have 72/8 teeth, not 66/8. To make sure, I search through my photo database, and find another Buren 12, and count the teeth of the fourth wheel, and, sure enough, it has 72/8 teeth!
What happened here? A bit more detective work – the Buren 12 is based on the Buren 1280. Ranfft tells me that the Buren 1280 beats at 19,800 b.p.h., but is otherwise pretty much identical. Gotcha! Somebody took the fourth wheel out of a Buren 1280, and put it into this movement.
Being very lucky, I find the right wheel on eBay, and a week later, it arrives from Italy.IMG_0870
With baited breath, I take a photo of the new and old wheel, and count teeth. I really got the right wheel from Italy, and now we’re ready to go!IMG_0873
The proof is of course in the pudding, and now the watch does 60 seconds in 60 seconds.
One of the more troublesome repairs we’ve had in the workshop so far, with an unusual problem indeed. With luck, I won’t encounter that one again πŸ˜‰
The dealer in the US is very nice indeed, and very sorry that the watch left him in this condition. He foots my entire bill, and everyone is happy.


21 thoughts on “Repair: Heuer Autavia / Buren 12

  1. A really good post really interesting. Wonder where you get the adapter bridles from as this is a really get around when springs are not available.

  2. I had a 1972 heuer Daytona before and that was a new old stock watch, that Cal 12 is just not a very well made movement compare to it main Rival of that Era the Zenith El Primero

    • I own a couple of these. Including the cal 3019 El Primero and a cal12 Breitling/Buren. I am not sure why you would discredit the Buren?
      Both designs have several flaws, and have had multiple modifications done over time. The El Primero is notorious for “eating itself up”.
      In all due respect they are both titans in terms of technical development. The microrotor automatic of the cal 12 is a gem and allows a slimmer movement. The El Primero is, with its 36.000a/h a true marvel.

  3. Hi Christian I am just wondering where you got hold of that mainspring adaptor bridle or did you make it yourself?

    • I had one from a watch where I fitted a proper automatic mainspring. I don’t think that you can buy them anywhere, but it shouldn’t be too hard to make one.

  4. What a great job. You should be proud of your talent! The devil is always in the details. Very interresting repair job.

  5. Wow, that was great detective work Christian. Too bad that the dealer who sold this watch lied about giving it a service. That seems to happen quite often.

  6. Documenting your fine work with pictures not only entertains us immensely, but in this case righted a wrong. Good job Sir!

  7. And THIS is why I send my most prized watches to you for service, Christian!

    Masterful detective (and horological) work, indeed!

  8. “The dealer in the US is very nice indeed, and very sorry that the watch left him in this condition. He foots my entire bill, and everyone is happy.”

    Great to see someone stand behind their word like that! And, as usual, great job, Christian!

    • There isn’t much you can do but to try to find a used plate that is better. The setting still worked, so I’ll leave that for another day to sort out. My idea would be to drill through, and to make a new post for the wheel that can be pressed into the plate.

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