I am currently working on a lovely yellow 6139-6002 for a customer which shows some pretty knarley amounts of wear on the barrel arbor pivot bushes.
The piece ran intermittently, and the customer stated he had to shake the piece to get it going all the time when it stopped.
A shake and a check on the timegrapher showed an amplitude of around 140 degrees, which shows the movement is in quite poor condition. Generally on a vintage piece, you want to see an amplitude between 200-260.
A quick explanation of why this is important is the amplitude of the watch is basically a measurement of how far around the balance can swing. The balance assembly is the “heart” of the watch and is the part that beats. A better swing on the balance means more accurate timekeeping and an ability to better cope with movement when on your wrist. When you move your wrist, the forces mixed with gravity change the speed of the swing, resulting in timekeeping abilities changing. The balance is primarily what regulates the beating of the watch and it is most critical this part is working correctly and within specification.
Anyway, to continue, I disassembled the movement and went through my normal COA routine. After some bubbling away in the ultrasonic cleaner for a while, I noticed weird filth in the bottom of the unit. I mean, dirt isn’t supposed to be circular shaped is it? The movement was absolutely filthy but this was odd.
On closer inspection, those bits were actually pieces of metal which had been shaved off from somewhere inside the movement. This is a really bad thing, as the metal mixes with oil inside the movement and turns into a lovely grinding paste. The paste destroys parts very quickly and with a piece like this, parts are starting to get scarce. A further inspection of the parts clearly shows where this came from.
So that is the top bearing for the barrel arbor pivot. Basically that is the shaft that the mainspring (the spring that powers the whole movement) wraps around. This is a critical part of the movement and has a lot of force on it. The bearing has been poorly lubricated, worn oval and the ratchet gear that sits inside the circular cut-out has worn into the plate. This has shaved off bits of metal which have got all the way inside the movement. Not good. Here is another view which gives a better impression of the complete piece.
Luckily for the customer, I had a good secondhand piece spare. If I didn’t, this easily would have added a minimum $100 to the cost of the repair. That’s assuming the part was even available.
After I replaced this plate and re-built the piece with correct lubrication, this is the result.
225 degrees amplitude. Quite nice for this piece. So there you have it. Get your vintage piece serviced regularly because otherwise you could damage parts inside which are hard to source or cannot be replaced. If serviced correctly, a mechanical watch should last 100 years or more, a lot longer than a quartz watch.