Need directions to find missing part

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Good afternoon from the Netherlands,
I have a Heuer 2447 with a Valjoux movement. The chrono wasn’t working properly and when opening the watch I found out a screw was missing. I have attached a photo and circled which screw is missing.
I was hoping one of the expert can point me in the right direction where I can find this little part.
Thanks in advance.
Jan

IMG_3640.jpeg
 
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Had the watch functioned properly prior to your detecting a problem? If it had, how long did you own the watch prior to the problem arising? Might the missing screw be buried somewhere in the movement? Or what are the chances the screw was floating around in the case, and when you removed the case back, the screw fell out? Check your work area with a magnet.
 
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That is not a screw - it's an eccentric stud that is used to adjust the depth of engagement between the chronograph drive wheel and the coupling wheel. It should be a slight press fit into the bridge, so not likely to have fallen out.

Step 1 is to identify the exact caliber...Valjoux 72 I think. Might be part 8400.
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Thank you! I checked everywhere but can’t find the part, must have been missing when I bought it. I recently received it and it wasn’t working properly right away.

It is indeed a Valjoux 72 movement. I will look for part number 8400 online, thanks a lot for providing me with the number.
 
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These parts have subtle variations on the age of the watch. The finish and shape of the bridges suggests late era production. This part can wrap around the wheel clockwise or counter clock wise. That affects how and where this plate is drilled. Sometimes this is called old style and new style.

Valjoux eccentrics do turn up from time to time. They can be really expensive. Often sold as 'rolex' parts. Sometimes it is more practical to get a parts 'assortment' which of course is much like treading water. Now one has two watches to search for parts.

Usually I see the eccentrics broken at the slot. They should fit really tight. Only turned as a last resort. Adjusting is usually done by pressing them out and pressing back in.

8400 does seem to be the part number.

Good luck.
 
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Thanks a lot, I appreciate the help. I ordered on eBay, I assume it is the right one.
IMG_3657.png
 
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I received the part I ordered at eBay.
Is there a special way to place the eccentric part?
 
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I received the part I ordered at eBay.
Is there a special way to place the eccentric part?

You will have to remove the bridge, and press the eccentric in - how you press it in depends on what tools you have. A staking set would work, or a Seitz of Horia jewelling tool.

In terms of the orientation, you might be able to get an idea by looking at photos of other eccentrics on the same movement, but in the end you will have top adjust this to get the right depth of engagement between the wheels in question.
 
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When using a stake to not hammer it. A light press with fingers that is all that is needed. I have found on the dismembered Landerons, that one can get it close before pressing it in all the way. Twisting with the slot can cause it to become loose or break the side of the stud.
Not sure if locktight is allowed. So far I have not had to do that.

Go slow and be prepared to repeat the adjustments many times with the balance and fork removed. A usb inspection scope helps. I saw that demonstrated at WOSTEP in the 1990s, when such things were really cutting edge.

The old books imply adjustments were made by hammering and filing the levers, so one does not really know what was done before. Before WWII mass stampings such parts were hand fit. I suspect that many of the post war mass produced stamped out ones got sometimes mangled by people following the old instructions. I have tools for shaving the bottom of screws. Not something I have used. So one also has be be careful about what screw goes into what hole. Most holes go all the way through the plate, so one has to check both sides for clearance. Many of the screws are keeper or 'safety' screws what hold the parts in place and keep them from falling out when the movement is jostled about.

I also often find the chrono bridge and the balance bridge screws swapped. The balance bridge screw is the longer one according to most data sheets. Chrono bridge screws are usually the same as the barrel bridge. Always check the data sheet.
 
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Not sure if locktight is allowed. So far I have not had to do that.

DO NOT use Loctite - these are meant to be adjustable!
 
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Thanks, I really appreciate the advices. I think it’s best to wait till my watchmaker is back from vacation and ask him to install it.. don’t want to mess it up :)