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Choosing the correct replacement crown?


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My latest project watch is a BFG 866, which states that it is (was) waterproof to 5atm. 

I have a stem but am missing the crown, there is no threaded tube on the case, so its not a screw down crown, but I’m struggling to find the right replacement.

The stem is 1mm diameter, the opening in the case is 2.5mm and I believe the crown should be 5mm. 

I assume the crown should have a tube with a rubber seal of some kind.....?

Am I best buying one of those cheapo eBay jobbies with assorted crowns?

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Edited by Robbie010
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29 minutes ago, Robbie010 said:

The stem is 1mm diameter, the opening in the case is 2.5mm and I believe the crown should be 5mm. 

Your watch has no pendant tube, so I don't see how it can be water resistant, unless you fit one. Beside that a pendant tube is needed to avoid the crown wobble and the stem bend easily. The tube is measured on the ouside diameter, to match the seal on the crown.

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I assume the crown should have a tube with a rubber seal of some kind.....?

Yes, so called waterproof, Swiss style. 

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Am I best buying one of those cheapo eBay jobbies with assorted crowns?

All assortments are very useful especially you intend to do a lot of resturations on watches that match the boxes you have. And having the right part ready to fit is a great achievement.  Look the table which lists the sizes, see if there's what you need before buying.

Otherwise Cousins has a good selection of individual crowns also.

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Press-fit a pendant tube in that hole, there's a special tool for this. That's going to leave you with a pendant tube OD of 2.5mm. The crown fits over this to form a waterproof with a rubber seal inside the body of the crown. You have chosen 5.0mm crown diameter, you still need to know the tap size (metric diameter of the threads on the winding stem, commonly 0.9 but also other sizes). Those 3 numbers, plus the finish (stainless, gold, etc) and the type (waterproof, swiss style, domed, etc ) will find you a crown.

Older, cheaper, non-waterproof watches just have a hole with no pendant tube and no seal, or sometimes a notch in the case rather than a hole, so the movement with stem fits into the case and a press-on caseback holds the movement and stem in place (often seen in "ladies" cocktail bracelet watches)

 

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On 1/16/2021 at 7:14 PM, KOwatch said:

Press-fit a pendant tube in that hole, there's a special tool for this. That's going to leave you with a pendant tube OD of 2.5mm. The crown fits over this to form a waterproof with a rubber seal inside the body of the crown. You have chosen 5.0mm crown diameter, you still need to know the tap size (metric diameter of the threads on the winding stem, commonly 0.9 but also other sizes). Those 3 numbers, plus the finish (stainless, gold, etc) and the type (waterproof, swiss style, domed, etc ) will find you a crown.

Older, cheaper, non-waterproof watches just have a hole with no pendant tube and no seal, or sometimes a notch in the case rather than a hole, so the movement with stem fits into the case and a press-on caseback holds the movement and stem in place (often seen in "ladies" cocktail bracelet watches)

 

Sorry to resurrect this thread but I’m still struggling to get my head around this and I suppose there is no point in me not getting to the bottom of my query while I’m trying to learn.......

My new Vernier Calipers arrived today so I measured the stem, which was 1.1mm. Now, this is the outer width of the thread so I assume the stem thread is actually 1mm. 

The case does not have a pendent tube fitted and you advise that I fit one - does that mean that the case would have originally had a tube fitted that has been removed?

If that is the case, once I have fitted a pendant tube should I use a crown with a tube or without a tube?

Also, if the watch case never had a pendent tube fitted, which type of crown would have originally been installed?.

Thanks. 

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15 hours ago, Robbie010 said:

If that is the case, once I have fitted a pendant tube should I use a crown with a tube or without a tube?

In horology terms, crowns do not have a tube, but can have a shorter or longer pipe. That is the part where the stems screws into.

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Also, if the watch case never had a pendent tube fitted, which type of crown would have originally been installed?.

Maybe one with a pipe long and wide enough to stay always in good contact with the case hole, to minimize wobbling.

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CousinsUK:

11 x Ø4.50mm x Ø2.50mm, SS

C528GZ1

 

1.1mm is a thread size. It's possible it didn't have a case tube, but it wouldn't have been water resistant.

Hard to tell from the photo but the caseback looks like a screw-on so decent WR is possible . How's the gasket? Definitely want to have  a look at that crystal also.

Edited by KOwatch
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18 minutes ago, Robbie010 said:

Is there any way of fitting a pendent tube / case tube without having to fork out £130 on the Horotec tool from Cousins??

As long you can find a way to press down straight it will be fine. Normally watchmakers have some sort of press that they adapt for various uses. Also consider if the watch you work on is worth to invest in new tools and which chances are of needing them again.

The Chines makes copies of various expensive tools

https://www.aliexpress.com/item/10000014322393.html

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