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Vintage Bulova Selfwinding mainspring questions


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Hi,

I've been servicing numerous Bulova 23 models with 10BOAC, 10BPAC and 10BZAC movements. All have "sealed" mainspring barrels. Up until this weekend, I've successfully opened, cleaned and reinstalled the original mainspring without difficulty and to good effect. 

This past week howver I opened a 10BZAC and discovered it needed replacement (broken in two pieces). Since NOS bulova 23 mainsprings are not available except as full replacements (i.e., sealed barrel), I decided to measure and order an equivilent from CousinsUK. All good so far, until I noticed the end of the mainspring and realized that I had ordered the right size but not sure I ordered the right kind (manual vs automatic).

My question is did I order the wrong type of replacement?

The first picture is the barrel with the bridle (sp?) pulled out. Notice it has a 'dot' that I assume catches the mainspring and the bridle slips to prevent overwinding.

The second picture is a a legacy mainspring from another model 23. Even though it says selfwinding (which I assumed is synonymous with automatic) it has what looks to me to be a tradition manual tip (i.e., facing the opposite direction of the wind to catch the bridle).

The third picture is the GR replacement I ordered from CousinsUK based on size (which is fine) and specifying 'automatic' since the bulova is 'selfwinding'. I know realize is a different tip, ie., this dual end shaped like a 'Y'. 

Can someone a) help me understand how this GR works, and b) can I use it without a problem as a replacement or did I order the wrong type of mainspring confusing "selfwinding" with "automatic"?

 

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1 hour ago, GuyMontag said:

The Emmywatch database says the 10BZAC takes a GR2936X mainspring. Is that the one you ordered?

That one is discontinued. I ordered GR2920x 

5 minutes ago, Levine98 said:

That one is discontinued. I ordered GR2920x 

So now I’m wondering if I should have left out the detached bridle since the GR mainspring is for an automatic and includes an attached bridle. I’d hate to have to dissemble and reassemble since so far the watch is running fine, but also want to do the job right. 

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As far as I know, automatic and self winding are the same thing.

Early self winding watches used ordinary mainsprings with an additional bridle to allow the spring to slip when it approaches full wind.

Eventually, mainsprings with integrated bridles were produced. There should be no issue using a modern mainspring with the attached bridle, as long as the size is correct. 

Cheers!

  • Thanks 1
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