PANERAI OPIII DATE ADVANCES ONLY HALF DAY

[Sassman]

I was able to diagnose an odd issue with my Panerai and thought I would share in case anyone ever experiences it also. 

After I performed a full service on my pam00091, which uses the OPIII movement. The OPIII is a modified Valjoux 7750/7765. After reassembly I noticed the date wheel would only advance half a day. Showing half of the previous day and next day. After verifying everything was properly lubricated I studied in more depth the way the date advance operated. Noticing something a bit strange I put it under the microscope. Low and behold there was a tiny microscopic crack in the date jumper.  It appears as if it was in the original part as the chrome plating follows the crack and may have been just enough to hold it together. Cleaning or bending it to reinstall looks to have been more than it could take. I have to imagine a fault in a part of this type is rare, but maybe not. 

Hope this helps someone in their search for a similar fault.

Edited April 15 by Sassman

[Sassman]

Well I spoke too soon. Here's where I am now with this issue.

I replaced the date jumper and all seemed to function correctly. Fully wound and only in the movement holder, no dial or hands, I let it sit untouched for two days. Both nights it advanced the date. The second night it might have been just shy of fully advanced. Seemed as though I fixed it, so I reassembled the watch. Three nights in a row the date did not advance. Once I pull the crown it does. So you might think that it's the dial interfering, but here's the weird thing. If I advance the date during the day to 11:57p and watch it get to 12:00:30a the date flips with gusto.

So here's what I'm thinking and could use your council. I installed a new Swiss mainspring. I used Moebius 8217 braking grease on the barrel walls. It seems to wind quite a bit before slipping, but does slip.  I've read that the 7750 really needs Kluber p125 as a braking grease. 

Do you think it just doesn't have enough power after a few to several hours of sitting before the date change?

Here are the TG numbers after service:

 Rate +1s/d,    Amp 301,    BE 0.0ms   

[ColinC]

I doubt it is due to lack of amplitude.  My 7750 - which I haven't serviced yet because the numbers were OK (and I am still scared of chronographs!)- has no problem flipping the date with an amplitude closer to 250º

On other movements I have had issues where the plate(s) that go over the calendar wheel interfere.  I did an FHF ST 96-4 last week where there are 2 tiny plates plus a larger plate that hold the calendar wheel in place and I had real problems getting the calendar wheel to snap around nicely.  Lubrication on the points of the teeth of the calendar wheel and making sure the small plates were aligned properly was the solution there.

[Sassman]

I will definitely look for interference when I open it back up. You make good points. 

The part that makes me wonder is the fact that it snaps around well if I do it during the day whilst I'm wear it and assume it has more 'wind' than at midnight. 

Edited 5 hours ago by Sassman