Balance pivots and Incabloc: safe installation techniques

[ifibrin]

After breaking the upper balance pivot (balance cock side) while replacing a new complete balance wheel in an ETA 2671, which ironically, came with a broken upper balance pivot, I came to a realisation about balance pivots and Incabloc. This was upon successful installation / replacement of another second new complete balance.

It turns out that leaving the lower (main plate) cap jewels inside the main plate incabloc shock block, when installing the balance cock is probably safer for both balance pivots. The bottom balance pivot can usually be seen visually to enter the main plate incabloc. While the balance cock cap jewels should be removed for easy visual verification that the upper balance pivot is safely in the balance cock incabloc during balance cock installation, leaving the cap jewels in the main plate incabloc supports the lower balance pivots. This ensures that the upper balance pivots don’t drop out of the balance cock incabloc during balance cock installation; if the upper balance pivot is out of the balance cock incabloc, tightening the balance cock screw will break the upper balance pivot.

Does anyone have any thoughts about my observations? Do they sound reasonable?

Edited October 7, 2021 by ifibrin

[Nucejoe]

I don't fully tighten the screw to the cock before seeing the oscilator run happy, even then I am careful and make sure to tighten in half turns and less as you approach the full tight.

 

[ifibrin]

15 minutes ago, Nucejoe said:

I don't fully tighten the screw to the cock before seeing the oscilator run happy, even then I am careful and make sure to tighten in half turns and less as you approach the full tight.

 

Hmm… that’s a good point. I previously installed the cap jewels only after securing the balance cock so without any of the upper or lower cap jewels the movement wouldn’t have started beating. Having the lower cap jewels installed would be functionally equivalent to your method, since it will only start beating if the lower pivot is in the jewel, and the upper pivot within the balance cock shock block.

Edited October 7, 2021 by ifibrin

[Nucejoe]

44 minutes ago, ifibrin said:

Hmm… that’s a good point. I previously installed the cap jewels only after securing the balance cock so without any of the upper or lower cap jewels the movement wouldn’t have started beating. Having the lower cap jewels installed would be functionally equivalent to your method, since it will only start beating if the lower pivot is in the jewel, and the upper pivot within the balance cock shock block.

Your method is good as long as one isn't blind folded when installing, it lets you see both pivots in holes ,oil and in short a preffered method. I don't see how you managed to break a pivot, possibly due to overconfidence with the method.

 Regs

[clockboy]

Fitting the balance complete can be a bit tricky but with practice it becomes a simplistic task.The adage don’t force anything when assembling is the best advice. When tightening down never fully tighten down but gradually test as you go. Everyone to their own method but I do not remove the upper or lower cap jewels until the balance is assembled and running. Then I remove and give them a final clean and lubrication. 

[ifibrin]

11 hours ago, Nucejoe said:

Your method is good as long as one isn't blind folded when installing, it lets you see both pivots in holes ,oil and in short a preffered method. I don't see how you managed to break a pivot, possibly due to overconfidence with the method.

 Regs

I broke the upper pivot the first time because I hadn’t put the hairspring in the regulator stud (etachron) when I replaced the balance wheel, and the cap jewels were not in the main plate incabloc. I suspect the hairspring wasn’t centred because the regulator stud was pushing the hairspring, and this pushed the balance wheel off Center; coupled with the lack of support from cap jewels at the bottom, the upper balance pivot fell out from the balance cock incabloc, and the upper pivot broke when I tightened the balance cock screw.

that was the first time I replaced the balance wheel in an etachron system. I guess you could call it the price for learning how to change a balance wheel!