Mainspring alternatives for 10BPAC

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BulovaBoy
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Joined: Sat Dec 08, 2018 2:24 pm

Mainspring alternatives for 10BPAC

#1 Post by BulovaBoy » Mon Feb 04, 2019 3:41 pm

Newbie here hoping to do some repairs. I have a couple of "project" non-spectacular Bulova 23s (10 BPAC) that I would like to start reworking. I know that there is a "lifetime" mainspring in these with a sealed "do not open" mainspring barrel. We all know that things don't last forever and are not unbreakable - especially after 60+ years. What is the correct mainspring for redoing such watches and/or alternatives per Bulova. It there a source for such mainsprings or another source. I guess I could settle for correct dimensions and do my own searches. Oddly, I can find no source for the correct mainspring replacement or a source......lots of 23s out there. Thanks for any assistance you can provide!

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JackW
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Location: Denver-metro area

Re: Mainspring alternatives for 10BPAC

#2 Post by JackW » Mon Feb 04, 2019 7:49 pm

The spring that goes in them is 1.30-.08-296 that is metric.

They are apparently a bit fragile and one needs a good winder to put them in.... so says the internet. I've not worked on one of these.

Places to try
- Twin City Supply
- Scott Watch
- posting on the vintage Bulova forum
- Casker - www.jewelerssupplies.com/
- https://www.esslinger.com/

I already looked at CousinsUK and Jules Borel.... they are out of stock.

Good luck!
All I know is based on hard work & writing by others. I can only aspire to augment this body of knowledge. If I am wrong it is because of my own failings. -me
"If I have seen farther it is by standing on the shoulders of giants." - Newton

BulovaBoy
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Joined: Sat Dec 08, 2018 2:24 pm

Re: Mainspring alternatives for 10BPAC

#3 Post by BulovaBoy » Tue Feb 05, 2019 10:28 am

Thanks. That is most helpful and definitely gives me a starting point. I appreciate your check of those two sources. I will connect with the others and see. I believe these are alloy springs also. So much for the lifetime spring pitch!

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SFC
Posts: 277
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Re: Mainspring alternatives for 10BPAC

#4 Post by SFC » Tue Feb 05, 2019 11:11 am

Is there a problem with your spring? I encountered the same issue the first time I worked on this movement. I thought it was interesting that the bestfit book states sealed barrel and doesn't include the mainspring dimensions. You can take the old spring out of the barrel to assess the condition.. if it looks ok and undamaged re-use the mainspring when you service the barrel and see how the watch runs. You can always re-do the barrel with a fresh spring if you are not satisfied with how the watch is running. The few that I have worked have been good runners.

BulovaBoy
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Joined: Sat Dec 08, 2018 2:24 pm

Re: Mainspring alternatives for 10BPAC

#5 Post by BulovaBoy » Wed Feb 06, 2019 5:14 pm

Good advice SFC! I guess I am expecting the worst. Also, perhaps I'm a bit lazy and thinking it would be best to simply replace the mainspring if I have it down that far. Having several of these it is probably wise to follow your thought during my first attempts. That said, at some point I will need a mainspring (or two or more). In addition, I have a solid 14K case that I would like to work up to repairing (or will have to send out). That one will get an overhaul with a new mainspring regardless of the condition of the existing spring. I can always reuse that original spring in another "more common" 23. But the gold with get the royal treatment....kinda like how it works in real life, right?! :lol:

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afire
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Re: Mainspring alternatives for 10BPAC

#6 Post by afire » Thu Feb 07, 2019 11:19 am

BulovaBoy wrote:
Tue Feb 05, 2019 10:28 am
So much for the lifetime spring pitch!
Well, to be fair, considering this movement hasn't been made in 60 years, there's a very good chance it did outlive the original owner. :lol:
Real men wear small watches.

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SFC
Posts: 277
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Re: Mainspring alternatives for 10BPAC

#7 Post by SFC » Thu Feb 07, 2019 5:31 pm

I think the "lifetime" and "unbreakable" came about because the improvement between blue steel and white alloy is night and day. It would have seemed like such a remarkable advancement to see these white alloy mainsprings for the first time. Fast forward to modern watch service centers... The standard practice is to throw mainsprings and even barrel completes into almost every watch. Even though the white alloy mainspring is still good it is not worth it to the manufactures to risk having to redo an overhaul over a faulty 10$ spring. Just imagine if the spring breaks in a manual wind chronograph your taking the entire watch apart and you will lose big time on the job.

Here is a pic of an "unbreakable" white alloy mainspring. It is severed in half and bursting through the barrel wall. The barrel arbor is in multiple pieces.. portions stuck in mainplate and barrel cover.
Anything watch related is breakable if it is put through harsh enough treatment
Image

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