I have an Omega Seamaster Cosmic Automatic which I purchased new in 1969. I recently took it from a drawer where it had languished for about 20 years and had it serviced at an Approved Omega Service Centre. It now exhibits a strange time-keeping anomaly which I would be grateful for any comments. When I reset the time the minute hand will lose anything from 2 to 5 minutes over the first hour, usually near the start of the hour while the second hand will keep perfect time. On one occasion the minute hand was completely stationary for 3 complete revolutions of the second hand. After this initial change the watch will be amazingly accurate over several days losing a regular 2 to 3 seconds a day – remarkable for this age of watch. I usually compensate for this behaviour by setting the watch 3 minutes fast, resulting in the watch settling to being correct to about a minute. I have no regrets at having resurrected what I have always felt was a very attractive watch but would be grateful for any advice on whether this fault is common and correctable.

 

How nice to be using your watch again after all those years and it's a true 'one owner from new'.

This is usually not a big problem and in my opinion, is likely to be a loose cannon pinion. It could also be related to a missing dial washer. Let's see what the real watchmakers on here say.

If it is the former, then it works like this:
The barrel containing the mainspring rotates and drives the 2nd wheel.
The 2nd wheel staff extends from the back of the mainplate , where the barrel drives it, through to the forward side, where the dial is.
The cannon pinion is a light interference fit on that shaft and attached to that is the minute hand.
So, the 2nd wheel shaft (staff) must turn if the watch is running but, if the cannon pinion is a loose fit on that shaft then it (and the minute hand) may not move regularly.

Solution is to tighten the cannon pinion but, this means a return trip to the service centre.

I had one watch where, if you shook it, the minute hand would move a few minutes on its own. That was very loose!

Hope this helps and let's see what the guys say.

Cheers, Chris