So I thought I was making good progress with my 1924 Princine 6N repair - case and dial cleaned, new glass fitted...
Given the age of the movement, the intended use as a dress watch, and my complete lack of experience, I wasn't terribly concerned about accuracy - just a watch which would run for a reasonable period of time at a speed approaching 1 hour per hour!
The movement was extremely dirty when I bought it, so I didn't really test it as recieved, but it would just about tick so I figured it should be a runner when clean. Unfortunately once cleaned, reassembled, and oiled, I couldn't get it to run for more than a few seconds. Then in the process of removing the balance during investigation, disaster struck and I bent the hairspring adjacent to the stud. When I tried to straighten it, even bigger disaster struck and it broke :-(
I suspect that also the balance pivots are bent as the balance does not run true, which might be the reason why it wouldn't run, but I need a bit more magnification and time to really look at that.
Also, I was concerned about the mainspring too - it remained quite tightly coiled when I removed it, but I don't know if this would affect running for a short period, or just the duration of running on a full wind, or maybe is just normal for a watch of this era. (See picture)
So here are my questions...
What are the chances that a balance from another contemporary 6 series movement (e.g. 6AP) will fit and work as a replacement? If not, is this movement based on something else that I might be able to get a balance from? I think that replacing the balance staff and hairspring are beyond my abilities and equipment; although I may be able to get a local watchmaker to do this, I suspect it may start to turn this into an expensive project.
Is the mainspring condition critical to troubleshooting at this stage, or just something to deal with later? (I have seen one for a 6N for sale on ebay, but not for shipping to the UK. It does show a picture with the specs, so I could buy one from Cousins using this data)
Does anyone have any idea why the 6N movement only seemed to be in production for one year - seems to be a lot of design effort for such a short production life.
I know I might end up just hunting down a contemporary movement and dropping it in wholesale, but I know I won't find a 6N, so it won't be "right" (whatever that means...)
Thanks for any advice,
Stuart
The 6N is a Sonceboz 246, and is the same ebauche used in the 6SN, but I doubt that this helps. There were a wide variety of oval movts used by many companies during this time period, but although they may look similar, they are certainly not interchangeable. Parts for these are not readily available, but you could fit a small hairspring of the same type from scratch. This doesn't fix the problem of the balance itself- you would have to find the correct staff. To correct these two faults is a lot of work, from the sourcing of the parts to the fitting.
My experience is that 99.9% of watches from this period are very very worn. This may be because of the Great Depression, when having your watch serviced became a very low priority for most people. Even with the new balance, you may have a watch that runs very poorly. Usually the jewels are very worn, as well as the pivots.
What I usually do, in cases like this, I scour eBay for replacement movts, or even complete watches. It may not be correct, but there may be other movts Bulova used in Princines that would also fit....
As always when it comes to watchmaking, I agree with Rob here. With movements like this, a harvester is usually the way to go. The combination of jewel problems and pivot wear from pieces this old generally forces you to choose the lesser of evils to cobble together the best running movement that you can.
Accuracy also has a huge amount to do with the fact that this watch was manufactured years before the more complicated hairspring alloys and mainspring alloys came about from about 1933 on (i.e. Nivarox, etc.)
Once again, I'm not sure any of this helps, but the best options would be to wait until a movement comes around, or get a certified master watchmaker to make you a new balance staff and comparable hairspring.