7751 day/date change problem

[watchfellow]

Hi everyone, 

I have a Valjoux 7751 where the day will advance about 7 hours after the date changes. Is this normal?

I am assuming it should change closer together, and I am assuming the issue is with the day date driving wheel.

Attached are photos of the watch (with and without the day disk attached). In the second photo, the driving wheel is in the process of changing the date. 

Thanks in advance.

[AndyGSi]

So at what time do the day and date change?

[watchfellow]

I haven't set the hands yet. But the day changes about 7 hours after the date does.

So if the date changed at midnight, the day wouldn't roll over until 7 am...

[AndyGSi]

21 minutes ago, watchfellow said:

I haven't set the hands yet. But the day changes about 7 hours after the date does.

So if the date changed at midnight, the day wouldn't roll over until 7 am...

Is this something you've just serviced yourself or did you but it like this?

If you haven't fitted the hands then how do you know it's 7 hours?

[watchfellow]

Just finished the service myself. I explained the situation wrong. I did set the dial and hands after service and then noticed the 7 hour difference in date/day changing. For the photos I removed the dial and hands.

I know that the 7751 has a delay with the moonphase function changing (which this one doesn't have), but I don't think the day and date should have such a delay (particularly 7 hour difference).

[nevenbekriev]

Fellow, the day and the date have separate driving wheels. You must put (mesh) them correctly when assembling the calendar. The difference of 7 hours is random number and the next time You assemble the calendar without taking in count how You put the wheels, it can be 3 or 16 or any other number from 0 to 24.

[watchfellow]

Hi Neven, thanks for the response. I originally thought there were separate driving wheels for the day and date functions, but it seems like on the 7751 the day and date driving wheel is responsible for both? I've circled it in red in the attached photo.

[AndyGSi]

1 hour ago, watchfellow said:

I originally thought there were separate driving wheels for the day and date functions, but it seems like on the 7751 the day and date driving wheel is responsible for both? I've circled it in red in the attached photo.

What you've circled is the Day Wheel while the centre is the Date Wheel and as
@nevenbekriev said they need to be set correctly as detailed in the guide.

Edit

I presume you've got the guide for all the other setting up procedures?

Edited September 11, 2024 by AndyGSi

[watchfellow]

Hi Andy,

I do have the technical manual but didn't see the page with the guide on assembling the calendar mechanism that you forwarded. That guide looks to be exactly what I need, so thank you! I will try to reassemble tomorrow and post an update on how it turns out.

[watchfellow]

Hmm.. I tried following the instructions as per the technical manual and I am still getting the same 7 hour difference between the date and day change. 

At this point the only thing I can think of is to try replacing the calendar driving wheel and see if that makes a difference.

[AndyGSi]

Have you followed the previous instruction for the rest of the movement?

Edit

Just had another think about this and if they're set as the diagram then one should drive the other so can't understand why the difference in time.

Edited September 17, 2024 by AndyGSi

[nevenbekriev]

OK, now I understand that the date wheel is actually in the center and the date is pointed by dedicated hand. Am I right? Then yes, the driving wheel is one for both date and day. Then, look why the position of date changing finger in this wheel is wrong. Obviously the day finger is placed as in the manual. But the date finger is not visible on the picts. When the day finger points right against the day star, the date finger must point against the date star. May be the date finger is not rigid, but loaded with spring and it has been for some reason blocked in wrong position and the spring can't return it to the correct position

Edited September 17, 2024 by nevenbekriev

[watchfellow]

I didn't get a chance to reply to this earlier, but I got a replacement date driving wheel and it works perfectly after I installed it. The date and day change at the same time now. The wheel appears to be composed of two different drivers and spring loaded, so my guess is somehow the two parts got desynchronized. Not sure how that would happen though. The calendar was non functioning before I took the watch apart, so I didn't pay much attention at the time.

Anyway thank you Andy and Neven for the tips!