Never serviced Jaquet-Droz

[Boz]

Eight months ago when I began my watch repairing journey, a relative passed me this unusual gold-plated pendant watch to "have a go". They had worn it daily for decades, till it stopped working (and had long gone out of fashion), and put it in a drawer.  At the time I had no test equipment but it was running slow and didn't run for long either.

Having opened the case to see what the movement was, I put in in a box of "future projects" as I wanted to continue practicing on junk movements.

Now I'm gaining confidence having serviced about forty movements and inexpensive watches, I thought it was time to repair it. This is what I saw on the time-grapher:

The movement looked clean:

Though the finish on the dial side is poor:

During the strip down I noticed some unusual wear to the underside of the centre wheel

I cleaned the movement and reassembled to try and see what was rubbing on the wheel. It was pretty obvious once I checked the play on the barrel:

I asked the owner when it was last serviced. The answer was I don't know, maybe never. I know it was worn daily for twenty or thirty years and dates from the 70s or 80s. I'm amazed that the only sign of wear I found was the top barrel pivot hole. OK time to order parts. I ordered a fresh barrel arbor, barrel bridge, and mainspring. The barrel itself showed no signs of wear or cosmetic damage. I think only the very tip of the teeth were catching the second wheel. It's a shame that I couldn't find a barrel bridge with the same finish. I've not posted pictures of the disassembly as it's a totally straightforward movement.

I cleaned, reassembled, inspected and lubricated (941/9010/HP1300/MolyslipDX/8200) the movement. For cleaning I use naptha and pegwood on the pivot holes,  followed by a three stage cleaning in an ultrasonic bath. I epilame the inca jewels, pallets, and escapement wheel. I use a superfine oiler and check each pivot under my microscope for correct oil levels and cleanliness. On this occasion I ran the watch for a few minutes, then lubricated the tip of three escapement teeth. I'm experimenting with different methods as I also like to remove and oil the exit pallet. I can't find a difference in results with either technique when you get it right. I probably make more errors oiling the ascapement. 

Putting it on the timegrapher. 280, 300, 320, 340 degrees, SNOWSTORM!!! Sorry I didn't get a picture but I quickly removed the movement as I could hear it knocking, in order to release the main-spring. I checked the replacement spring and it's measurements were the same as the original however the curve was a little less pronounced. It looked fine, I'd simply replaced it as a matter of good practice. So I cleaned the original and put it in.

Now the timegrapher results show unexpectedly high amplitude, but it's not knocking.

Dial down

 

Dial up was within a second and two degrees of dial down, and the other vertical positions were similar to the crown right.

On reflection, this watch will spend almost all of it's life crown up, so I readjusted it optimised for that position accepting a greater error dial up and down. After a few hours of running-in the differential between the horizontal and vertical positions has reduced. The various vertical positions all perform similarly so I won't post them all. These are after an hour or so of running:

So I learned a few things on this movement. Firstly I should have picked up on the play in the barrel as I disassembled the watch. Then I've have known as soon as I saw it the cause of the marks on the second wheel. Secondly, I learned that a new spring even of apparrently correct and identical specification may cause knocking. Finally, a lesson I learned early in this journey (taking care of the dial) remains visible on the face of the watch, where I marked it as I opened it all those months ago. You can only see it under a lupe, but it's there on the seconds dial between 15 and 20 seconds.