Just had my 2007 3570.50 (1861 movement) serviced by a local watchmaker. I noticed that before the service, I could put slight backward pressure on the crown and stop the seconds hand (or even go backwards) during setting. Then a slight rotation forwards starts the seconds again. I used this to sync the second hand to the time reference.

I understand this is normal behavior for the 1861.

However, after the service, I can no longer do this; when I pull the crown to set the time, back pressure no longer stops the seconds; it keeps going no matter what. Is this expected?

 

It is to be expected.
The potential to " hack" the 1861 is dependent upon the tension on the Cannon pinion.
Are you trying to hack the movement at a full wind of the Mainspring or a partial wind?
I ask because the ability to hack the movement is improved with only a little power in the Mainspring. At full wind it may be impossible. My 1861 is like this as well as my Seiko with the 7s26 movement. When new the 7s26 was hackable at full wind but after some wearing in, that changed.
They all vary from one watch to the next and it may become impossible to hack after some wear occurs over time.
The situation with your watch can be fixed or improved with some very judicious adjustment to the tension. But it can be a bit of a lottery in that a little can be a lot more than desirable and not enough will never really be right.
In summary, the adjustment is simple to do, but difficult to do well and it may not be worth the watchmaker's time to pursue as it's a sort of a rabbit's hole in some respects.
Archer will be able to shed more light on it

How's the timekeeping?

 

Wow, thanks for the detailed response!

I was trying to hack on a full wind. This isn't important to me; I just wanted to make sure it wasn't an indication of a poor service.

Timekeeping - he provided me with the timegrapher output post-service: +004/+006/+001/-002/+009. Not really thrilled with these numbers (+9 secs?), but I guess they are all within spec. I just picked up the watch on Saturday so I haven't had a chance to check the accuracy on the wrist over the longer term.

 

They appear to be nicely within spec
Enjoy that baby for all it's worth
Was it an independent watchmaker or Omega?

 

Thank you! I'm the original owner, bought it in 2007 and love it more than the day I got it. This was its first service, as after 15 years it started gaining one minute per day. I took it to him, and he said not only was the rate poor, the amplitude was really low (121 degrees)

He's an independent watchmaker, but Omega trained. He was real chatty and happy to show me pics of him in a white Omega lab coat getting co-axial training at some official Omega building (may have been Switzerland). He also sends a pic of your completely disassembled watch before cleaning. It was a shock to see to say the least!

 

She was well overdue for a service then.
A good outcome overall and a good experience for you. Just the way it ought to be
Enjoy

 

Guessing that after the watch wears in a little bit, you’ll find that the canon pinion loosens up slightly and allows hacking again

 

Thanks. It's no big deal, I don't really need the hacking, just wanted to make sure it wasn't an indicator of a bad servicing, which sounds like it isn't.

 

That would lessen the ability to hack, not allow it to happen.