I recently obtained a 21 jewel Bunn Special (sn 2895528). It wanted to run, but wouldn't. The only thing I could find wrong with it was the safety table wasn't completely seated and the beat was not set properly. I tried to finish seating the safety table, but it wouldn't move. So I decided to restaff it. It now runs for a minute (or so) then stops in either dial up or dial down. With the main spring let down, the balance moves freely in all positions. As soon as I wind the main spring, the balance stops. I put a balance from another Bunn in it, and it operates the same. I am bewildered by my Bunn. Any suggestions? Could it have too strong of a main spring in it? Thanks

Again, Mark, it's almost impossible to diagnose problems without the watch, but...

I assume that you have cleaned it.

I couldn't know what the problem actually was, but upon your statement that the balance is free and another balance had the exact same problems.... I'd look to the power train.

I have had similar problems and have traced it to the mainspring barrel. The 16 size Bunns use an annoying system of 3 screws to hold the barrel. Tightening this system... it is very easy make the barrel slightly tilted. That will cause the mainspring barrel to bind. Dont't forget that the mainspring-barrel assembly is the first-wheel of the power train.

What I would do would be to remove the balance and set it aside. I would take-down power and remove the mainspring barrel and the pallet. Then I'd carefully check the rest of the power train to see if it is running free. If it has been cleaned, it may still suffer from a bent, damaged or improper wheel. It is is free... I would then concentrate on the mainspring barrel. Is the cover COMPLETELY set and level? Then, I'd reinstall the mainspring barrel, making certain that it is set level and proper. Without wind... the mainspring barrel SHOULD have a tiny bit of end and side shake. Don't forget to oil the pivots of the mainspring barrel, as you would any pivot in the power train.

At this point, before reinstalling the pallet, I would give it a backlash test. Put a few clicks of power on the mainsrping. The power train should wind-down and.... at the end of it's wind down, it should reverse direction for a bit. The Bunn's are so finely made that the backlash should be rather pronounced (with some, I actually get TWO reversals of direction). If you are getting backlach, in this test, you can be 99.9% certain that it's not the power train.

If I had to guess... I'd say that there is a problem with the mainspring barrel. It's happened to me and I am now very careful.

An incorrect mainspring can cause problems but I would not expect it to stop the watch... unless it was physically broken.

Thanks - this gives me a plan of attack. I'll let you know how it goes.

Well, I thought I had it. I noticed that one banking pin was a micto tad taller than the other. So I compared them to another Bunn and adjusted them accordingly. What a difference. The watch ran great for about 4 hours then started operating the same as it did before. What a puzzlement.