Reassembling Balance in a Bunn

Marv

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Jan 29, 2021
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I removed the balance wheel and hairspring from my Bunn, cleaned it in One-Dip and re-oiled the jewels as an experiment. The watch was running fast by about 2 minutes a day and the amplitude was piss-poor (about 160). Beat error 2 mS.

Well, I got it together and it is running (amplitude is about 270 now and the watch runs about 5 s/d fast and the beat error 0.8 mS)). If you can't be good, be lucky.

The question is, how does one properly install a balance wheel? My concern is getting the pivots into the jewels without damage.

What I did was drop the balance into its lower jewel and then lay the top assembly over the balance pivot and try to fish the pivot into the jewel. I can't really see the pivot, so it seems like a hit and miss prospect. That's my issue.

Using a bulb blower I checked that the balance would oscillate and then kept tightening the screw to clamp down the upper assembly until it was snug.

Obviously, I am a total newbie here. Is there a better way?
 

Repivot

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Been repairing watches for a living 25 years now. The way you describe is essentially the way I do it too. Before the last tightening of the screw, look from the side and make sure the balance wheel isn't crooked, but level.
 

darrahg

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Way to go Marv. It reads like your are doing ok. FWIW, I always have the balance rotating, after positioning, while tightening down the cock. That way, if it suddenly stops I stop tightening the screw immediately. I then adjust the balance, get it rotating again and commence tightening. I repeat until the cock screw is tightened. This procedure will eliminate the use of a blow bulb. Take your pick and enjoy!
 
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Skutt50

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What yo described is what I would do when possible.

There are however some situations where this does not work well for me.

One such situation is when the regulator pins are of a type where you close them around the hairspring. In such case I instal the balance in the cock and lift both into the movement. Holding the balance at 90 degrees before lowering it will allow me to get the impulse pin on the correct side of the paller fork. Then it is a matter of gently wiggeling the balance wheel in place while slowly tightening the screw for the balance ccock.

Another situation when I install the balance on the cock is when the stud is tight and will not slip in place easily. Instead of "modifying" the hole/stud I install the balance in the cock on the bench.

When lifting the balance/cock in place I try to avoid having the balance dangle in the hairspring. I lift both together and roughly place them is position. I can then fine tune the balance position and make sure the fork is on the right side of the fork etc.
 
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Marv

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Been repairing watches for a living 25 years now. The way you describe is essentially the way I do it too. Before the last tightening of the screw, look from the side and make sure the balance wheel isn't crooked, but level.
Thank you, all. Those pivots are about the same size as frog hair. A bit scary.

I am not sure about the alignment of the impulse pin (roller jewel?) with regard to the pallet fork. I think I got lucky on that as well. When assembling, should I make sure the pin is in-between the fork?

I am assuming so, or will it self correct when the watch is wound up?
 

Skutt50

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The impulse jewel has to be on the "correct" side of the pallet fork or you will have a watch that is overbanked!

I usually give the crown a wind or two so the pallet fork will snap and rests against one of the banking pins.

Now when lowering the balance the impulse jewel should be inserted as if it has passed the pallet fork i.e. inserted towards the side where the pallet fork is resting. That way it will have fair chance to enter into the pallet fork and move the fork towards the other side when you start the movement. If you get it wrong it will meet a fork that won't move and the watch will not run.

You could try to fix this before you insert the hairspring stud in the balance cock but it will mean you have to rotate the hairspring (and balance) one turn. The stud have a tendency to get stuck several times during the rotation so I would rather lift the balance and re-instal.

If you got it right the first time, congratulations. Without paying attention you will get it right half of the time.....
 
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Marv

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Jan 29, 2021
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The impulse jewel has to be on the "correct" side of the pallet fork or you will have a watch that is overbanked!

I usually give the crown a wind or two so the pallet fork will snap and rests against one of the banking pins.

Now when lowering the balance the impulse jewel should be inserted as if it has passed the pallet fork i.e. inserted towards the side where the pallet fork is resting. That way it will have fair chance to enter into the pallet fork and move the fork towards the other side when you start the movement. If you get it wrong it will meet a fork that won't move and the watch will not run.

You could try to fix this before you insert the hairspring stud in the balance cock but it will mean you have to rotate the hairspring (and balance) one turn. The stud have a tendency to get stuck several times during the rotation so I would rather lift the balance and re-instal.

If you got it right the first time, congratulations. Without paying attention you will get it right half of the time.....
Thanks! I am eager to learn and the book I have along with some of the videos I have watched do help, but sometimes there are little things that nail all the details. People here really help fill in those voids!
 

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