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Valjoux 7750 Date Only to replace Day/Date?


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Hello WRT! Glad to have found your site, the resources here are incredible for a beginning hobbyist like myself. 

I purchased a project LeJour 7000 (Valjoux 7750 powered) that is currently running hilariously fast- something like +2 hours per day. I purchased it with the intent to drop in a modern, more decorated 7750.

The LeJour has a Day/Date dial (Seen here) but I've found a date-only 7750 that would fit the bill. Is it possible to use this movement and just add the day wheel from my current movement? Is the underlying hardware all there?

Even better, what is the best way to research the parts necessary to do the conversion?

Thanks all!

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Don't know unless you provide pictures of the spare movement I'm afraid. You will need a jumper, driving wheel, and dial washer in addition to the day wheel. It's a crapshoot whether or not you get all, some or none of these parts included on a movement meant for date-only. More than likely you're going to need to transplant at least some of these parts to the one you intend on using from the extracted movement.

If it was up to me I would try and save the old movement. Taking the original Valjoux out of this watch and sticking in a modern ETA would likely have a negative impact on its value.

Edited by CaptCalvin
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You need a copy of the tech manual for the 7750. There are many floating around. This will tell you what you are missing and how to put the assembly in. I have added several day comps to 7750s......its quite easy. As far as swapping movements it probably comes down to the fitment ie the watch movement ring. From what youve described it may be a fairy 1 to 1 swap. If im understanding you correctly youre gonna have a dial with a missing slot or vice versa. If you pm me your email I will send you the tech manuals. The 7750 is the one I specialize in......or rather its the one I started out working on and have spent the most time with.

Sent from my SM-G950U using Tapatalk

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@CaptCalvin - I don't have a spare movement on hand, I was looking at buying a 25 jewel out of a Montblanc Meisterstuck which seem to be plentiful and relatively cheap. Here is an example with some photos. 

@Bauertime  - I will do some reading on addressing the hairspring, if it's a single part that needs to be addressed I can give it a go, but the watch has unknown service history so I'm not sure how worn the remainder of the movement is.

@bjd1020 - Thanks for the help! Yes, the concern is the blank space in the day slot. Is there a great deal of variance in movement sizes between 7750s that lack additional complications?  

 

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4 hours ago, Displacement said:

@CaptCalvin - I don't have a spare movement on hand, I was looking at buying a 25 jewel out of a Montblanc Meisterstuck which seem to be plentiful and relatively cheap. Here is an example with some photos. 

@Bauertime  - I will do some reading on addressing the hairspring, if it's a single part that needs to be addressed I can give it a go, but the watch has unknown service history so I'm not sure how worn the remainder of the movement is.

@bjd1020 - Thanks for the help! Yes, the concern is the blank space in the day slot. Is there a great deal of variance in movement sizes between 7750s that lack additional complications?  

 

If you're going with the example in the link it does come fully equipped to take a day wheel with exception of the washer that ETA lists as "indicator distance piece". Your LeJour should have it. It's a little silver washer that sits on top of the day wheel so do keep in mind to transfer this part over.

7750 and derivatives should all be the same size with the exception of the Valgranges line (wider diameter) and that alarm-equipped one that Fortis modified that added considerable height.

Edited by CaptCalvin
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This thread has been incredible! Thank you to all of you for your help, you have built an incredible resource on this site and it has given me confidence to take this on.

My plan is to demagnetize the current movement, see where that and an adjustment get me, but replace the movement temporarily. The long term plan is to service the movement myself. Looking forward to learning more from you all!

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