Speedmaster 1861/861

An 861 can certainly be regulated to better timekeeping than +20 SPD. The 861, 1861 and 3861 are all good movements. The 3861, being relatively new, has had one known issue with some of the early production models that Omega has repaired under warranty for affected models. The co-axial movements are not any more or any less prone to breakdown than any other modern movement. I’ve had experience with three different Omega co-axial movements. All were reliable and extremely accurate with no mechanical issues.

Since the watch you see advertised is an 861 (which Omega stopped using in the early 1990s when they switched to the 1861), the watch likely needs a service which is why it is running so fast. After a service and regulation, it will keep reasonably good time (± 10 sec per day), but might be more variable.

The 3861 is a chronometer METAS certified, so has better timing tolerances and SHOULD be + at less than 6 seconds/day. It also hacks, so is easier to set the time accurately. That is harder to do on the 861/1861.

So, if you want a chronometer-grade Speedmaster, get the 3861 or one of the automatic versions. If you are willing for the timing to be a little more variable, the 861/1861 is a great and reliable option.

The other thing to consider is that many watchmakers will work on the 861 or 1861, but won't work on the new Co-Axial movements because they chose not to go through the extra training. Mine is an example -- he has plenty of work on Rolexes and ETA-based watches, that he chose not to mess with the new co-axial movements, even when the shop he works for was an Omega AD. I wouldn't trust someone working on my co-axial movement without the training and proper equipment.