How many hours in a day? Watch Day/Date Changes Every 26 Hours!

[Waggy]

I have a Seiko 7009A non-runner which I have had for a while and thought it was time to restore/refurbish - all going well, I install the dial and then I rotate the crown until the date clicks over and then install the hour hand, I rotate the hour hand using the crown just to make sure it isn't fowling anything and notice that the date now flips at 2:00 am, 26 hours from the original position..... Silly me, I must have messed up and I reinstall the hour hand, again it flips at 2:00 am, thinking I am loosing my mind I rotate it again and this time it flips at 4:00 am...then 6:00...Pulling my hair out I decide to leave it for the day and watch TV.

My thinking is that a Frankenstein "7009A" has somehow found its way into my collection and I have a rogue wheel with a gear ratio error somewhere, or does anyone else have any other ideas? Or know the best way to troubleshoot so I can find the rogue wheel/gear?

[watchweasol]

Hi Waggy  have you installed the day/date finger and gear correctly.  If you dont have the tech sheet I have attached it below.  Depending on the watch they usually start about 11 30/45 pm  and complete 12 30/45 am there are others that vary.

277_Seiko7009A.pdf

[Delgetti]

I agree it sounds like wrong gear ratio. Here is what I would do:

Count teeth on hour wheel, intermediate date wheel and date wheel, calculate gear ratio, should be 0.5

If you find wrong ratio, google for pictures of the 3 parts and find out who is the bad boy. My first candidate would be the intermediate with its two layers.

 

By the way: Did you check with a loupe if all teeth are ok?

[Waggy]

Found the problem, the small plastic gear had stripped teeth, see picture at 10:00 O'clock (apologies for blurry picture). The order of the universe is restored and a day once again has 24 hours.

Thanks to everyone who helped.

[Waggy]

So this happened to me again last night when putting the hands on a Citizen 6651A, 26 hours in a day - then it dawned on me what the issue is... of course it was 100% my fault! So here is what causes this:

1. When I put on the hour hand at midnight I turned the hand 24 hours with the winding stem to make sure that the date turned over at midnight, but the hour hand must have been sitting at an angle or slightly low and hung up on the 9 O'clock marker
2. I adjusted the hand and spun it again for 24 hours to make sure all was OK (no hang up this time), but noticed that the date changed around 11:30, not midnight
3. Here's my mistake, instead of removing the hour hand I simply bumped it forward 30 mins by pushing it with a piece of peg wood
4. I then spun it again for 24 hours to make sure all was OK, but noticed that the date changed around 1:00 am, not midnight
5. Here's where I compounded my mistake, instead of removing the hour hand I simply bumped it back 1 hour
6. Now when I then spun it again for 24 hours to make sure all was OK, I noticed that the date now changed around 2:00 am, not midnight.... and so on
7. Eventually I gave up and went for a coffee

Whilst drinking my coffee it dawned on me that the lazy bumping back and forward was not slipping the hour hand on the hour wheel, but instead stripping the teeth off the cheap plastic date change gears! So tonight I have to change them out, fortunately I have a donor watch I can steal from. I'm mad at myself for my lazy mistake causing more work and problems and burning parts, but happy that I solved the mystery! Hopefully others can learn from my mistake:

Edited October 24, 2023 by Waggy