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A Brevet Rebuild


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I had to recondition some Twinlocks for various projects & I thought others might find a tutorial useful.

The Problem
The spring action that ejects the crown from the case tube when the crown is unscrewed for winding/time-setting is not working, the crown feels like it is slipping during winding, or you are unable to fit a stem because the tube shaft is damaged or the threading stripped

In either case, your options are to replace the crown, recondition the crown's internal components or transplant them from another crown. Once the crown is disassembled & the individual components are cleaned & inspected, you can then decide whether they can be reconditioned or whether you will need to replace them (I am not aware of a source for replacements for any of these components, so transplanting is the only real option - note that while the tube shafts may be interchangeable between like crowns, the shaft diameters often differ between the various crown versions, which may require refitting of case tubes & gaskets).

Crown Disassembly
To disassemble the crown, secure (snug, not tight - too tight & you will deform the shaft) the tube shaft in a vice (a pin vice will also work) & unscrew (counter-clockwise) the crown cap from the tube shaft. In most cases, with the tube shaft secured, you will be able to unscrew the crown by hand. If not, use a pair of rubber-jawed pliers (if you use metal-jawed pliers, be careful not to scratch or damage the crown's surface)

After the crown is separated from the tube shaft, you can remove the inner plunger & spring assembly (I needed to transplant the spring assembly from 1 Twinlock over to another, so what you see below are the components from 2 Twinlocks)

Tapping a Stripped Stem Hole
If the stem hole threads are stripped, you may be able to rethread them with a Crown Reamer. This is essentially just a tiny tap that you screw into the hole to freshen the threading. Fortunately, in this case, it was successful


The Cleaned/Reconditioned Parts Ready for Reassembly
When reassembling, do not overtighten the tube shaft into the crown - hand-tighten (with the tube shaft secured in a vice) only

The Reassembled Brevet Crown




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Thank you freddy333! I never knew that these could be disassembled like this. I have several triplocks which were set aside due to various defects. Perhaps I'll be able to salvage one or two of them.

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Amazing! That's pretty cool information- the anatomy of a crown.

Muchas Gracias, Freddy!

Thank you freddy333! I never knew that these could be disassembled like this. I have several triplocks which were set aside due to various defects. Perhaps I'll be able to salvage one or two of them.

You are very welcome. Hopefully, you will be able to salvage some of these valuable parts & put them back into service.

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Great info and pictures!

I figured I was the only one who took these things apart. :p

A few tips learned by trial and error (mostly error):

If there is a "ww" lathe and collets available:

a...find a collet that the crown post just barely slips into

(crown post = the tube that the crown cap screws onto, not the stem tube)

b...mount the collet in the lathe

c...slip the crown post in the collet

d...tighten the drawbar down to hold the crown post

e...hold the headstock and unscrew the crown cap

Since the collet is a precision fit, the crown post will not be damaged at all.

I checked and a standard 6mm or 7mm crown post fits in a #22 collet and a 5.3mm crown post fits in a #18.

You can make a tap 10 (.9mm) thread tap out of a T10 stem (standard Eta/rolex) by tapering the end down a little and grinding or filing a flute (chip groove) in it like in a regular tap using a small commercial tap for a sample to go by (only one flute is needed).

Chuck the "stem tap" in a pin vice and try the tap, if it binds up...back it out and make sure it is not blocked and try again (see notes below).

Do not leave much tap sticking out of the pin vice because it allows the stem to twist and break easier.

"Stem taps" only work in soft metal or where threads have already been cut and just need cleaning or straightening.

Use Loctite on the crown post threads on final assembly.


a...before tapping -- poke a pin or something into the stem tube to make sure there is not a stem broken off in the tube or it is full of lead, glue, dirt etc .

b...lead chips are often used to "pack" crown threads so the stem will still bottom out if the stem is a bit too short

c...it's a good idea to bottom out stems in mechanical watches so the stem will not tighten into the crown when winding the watch

d...quartz watches do not need to bottom out as long as the stem is stuck with Loctite etc

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  • 2 years later...

Pretty amazing, the level of skill demonstrated on this site.

If you went to VRF and asked them how to rebuild a 6mm Brevet crown, do you think anyone would have an idea?

Not likely. And you'd become a pariah for having the temerity to even consider doing it.

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Don't sleep on Nanuq, AK winters are long, Plenty of reading on the bowl? :D

I have to agree with the man. The insightful and very precise information found here is to no comparison elsewhere. This thread alone can save many people time, heartache and money. Now, if only there was a listing of compatible crown:parts that will be ideal.


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