Junghans J30BZ cockpit chronograph

Todays article features a Junghans cockpit chronograph which dates from the WWII era. It arrived in a bit of a sorry state, flooded with oil, quite a few parts missing and it’s been hacked about a bit in its long life with scratched plates and bruised screws. However the fact it survives at all is a minor miracle! The brief was to try and get it running, but not to throw too much (any!) money at it. It came with a donor movement which provided all the missing parts. The instrument itself has a rotatable ‘count up’ bezel a chronograph with a centre seconds sweep and 15 minute sub register. The chronograph hands weren’t delivered with the watch but I’m assured the owner has a set. The knurled wheel at 6 o’clock serves two functions, the first is to wind it up, the second is activated by pulling the cord attached to a lever by the wheel. Once this is pulled down the wheel can be used to set the time, once it’s set the lever can be pushed back in. The brass button below the wheel starts, stops and resets the chronograph.

Junghans J30BZ chronograph

The back is plain and has a bayonet type fitting, just twist, pull and off it comes.

Junghans J30BZ chronograph

We can now see the movement which is a low beat, weighted balance, column wheel chronograph.

Junghans J30BZ chronograph

With the movement removed from the front I removed the hands ready to take the dial off.

Junghans J30BZ chronograph

Once the dial and dial housing was removed the rocker assembly that switches from winding to time setting is visible. Note the piece of chain link fence acting as a click spring!

Junghans J30BZ chronograph

This was soon stripped ready to tackle the motion work on the other side.

Junghans J30BZ chronograph

The first thing I noticed was the lack of a centre chronograph wheel, no indexing finger on the minute register wheel and the balance had all it’s rim weights removed apart from four. I think the balance isn’t from this particular movement and has been adapted to fit, I’ll see how it works later on. Everything was dripping in oil which is a double edged sword, it means the movement won’t run but it also means it’s been protected from the ravages of rust!

Junghans J30BZ chronograph

I stripped the chronograph levers and wheels which allowed me to remove the train bridge. Can you spot any other issues with this?

Junghans J30BZ chronograph

The centre wheel has a missing tooth, quite a common occurrence with these old high torque movements.

Junghans J30BZ chronograph

The mainplate was soon stripped…..

Junghans J30BZ chronograph

….and the parts were ready for the cleaning machine. I’d already cleaned all the excess oil off in essence of renata, this way the cleaning chemicals in my machine last a lot longer.

Junghans J30BZ chronograph

The parts came out a lot cleaner than I imagined they would, must have been all that pre-cleaning!

Junghans J30BZ chronograph

Junghans J30BZ chronograph

Junghans J30BZ chronograph

Reassembly started with the huge mainspring.

Junghans J30BZ chronograph

A replacement centre wheel was harvested from the donor, you can see the original had been cut down for reasons I can’t fathom so even with good teeth it would have needed changing.

Junghans J30BZ chronograph

I refitted the train….

Junghans J30BZ chronograph

….then the bridge, pallet fork and balance. However it still can’t run yet as I can’t get any power into the mainspring yet so that’s the next job.

Junghans J30BZ chronograph

The ratchet wheels and assoiciated levers were refitted and the donor movement provided a proper click spring.

Junghans J30BZ chronograph

This spacer around the circumference gives support for the dial.

Junghans J30BZ chronograph

The chrono wheels and levers were rebuilt and the watch put on the timing machine. Even with the regulating lever fully retarded it was gaining 10 minutes a day! As I suspected the balance wasn’t designed for this movement, the reason the weight screws had all been removed was to reduce the mass to allow it to run faster, it seems whoever did it removed too many.

Junghans J30BZ chronograph

Luckily the donor had a useable balance wheel.

Junghans J30BZ chronograph

This was fitted and the movement was rehoused. Note the minute register detent spring and centre wheel, these were also harvested from the donor. Setting the depthing of the coupling wheel was a bit hit and miss as two of the eccentric cams were seized, I managed to get it set by gently bending the lever and it now works beautifully. Definitely not to be recommended but given the brief it was all I could do.

Junghans J30BZ chronograph

Pop the back on and she’s finished. With the correct balance it’s keeping remarkably good time, however the positional variation is a lot larger than I’d like but considering where it started from it’s not bad at all. I wish the owner had sent the chronograph hands as it would have been nice to see them running but I’m sure they will be the first things he fits when it gets back. It’s interesting to ponder what aircraft this came out of, bomber or fighter!

Junghans J30BZ chronograph

Junghans J30BZ chronograph

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