cal.751 750-1572 friction spring for day star dial and positioning the day star driving wheel

noless · May 14, 2022

I have recently been servicing a 752 and a 751 and while going through the parts list I discovered that I am missing the friction spring 1572 in both of these watches. I was wondering if anyone (well @Archer really) could tell me if this is due to an update or if I should be looking to get a pack of dial washers for these movements.

A related question, how to align the day star driving wheel so that the day changes when the date changes?

Archer · May 14, 2022

The dial washer isn't used on these day/date calibers, as the upwards travel of the hour wheel is already constrained by other parts.

In order to sync the day and date change, assemble the calendar to this point:

In the hand setting mode, turn the crown so that the time advances until the tooth on the date indicator driving wheel is just touching the tooth of the date indicator as shown by the arrow on the left. Then adjust the day indicator drive wheel finger so that it draws a straight line to the cut out on the cover plate for the day jumper spring - as shown above.

Then finish the assembly:

And test the sync - if it needs adjustment, remove the day indicator and make a tweak, and try again. When done right, it should look like this:

Cheers, Al

kaplan · May 14, 2022

Correct me if I'm wrong but here's my theory, I believe there are 2 models for these, flat/older design that needs a washer and a newer design with a spacer

This is the flat one and the washer:

This one is I believe similar to the one in the video:

With the spacer protecting it:

It was my theory that the spacerless older design could be more prone to cog slips as well

Edit: Or could it be a 752 vs. 751 thing with the 751's getting the better designed part? I didn't pay attention to where the parts came from, the serial years etc.

noless · May 14, 2022

Thanks for the information and photos @Archer I hadn't realised the day indicator drive wheel finger could be moved independently of the wheel, but in retrospect that it is listed as "with finger assembled" in the parts list I have it seems obvious now.
I was thinking I would have to repeatedly take the indicator guard off and reposition the wheel, but felt that there would surely be a more efficient method since these were mass produced movements.

I think you might be onto something @kaplan looking at both of my day dials they are these ones with the raised inner lip/flange, I had been thinking that a dial washer here would really introduce a lot of power drain at midnight when all of these indicators need power to change, so perhaps the older design with the dial washer was changed because of this?

After learning that there are 4 revisions of the date indicator driving wheel, I take a bit longer to investigate instead of just going with what a photo copy of a print from 1967 says.

Archer · May 15, 2022

kaplan
Correct me if I'm wrong but here's my theory, I believe there are 2 models for these, flat/older design that needs a washer and a newer design with a spacer

This is the flat one and the washer:

This one is I believe similar to the one in the video:

With the spacer protecting it:

It was my theory that the spacerless older design could be more prone to cog slips as well

Edit: Or could it be a 752 vs. 751 thing with the 751's getting the better designed part? I didn't pay attention to where the parts came from, the serial years etc.

I can’t see clearly what the “washer” is in your first photo, but as I said these don’t use a dial washer.

The day indicator was redesigned to extend the pipe as your second photo shows, and this was deemed a mandatory replacement part in 2015. So this is a relatively new change that applies to all versions of the movement.