..HELP NEEDED !!....501 movement information...

The 500 (US version w OXG mark like yours) had 17j. The ROW 501 had 19 then 20j. I’d suggest yours has had some parts changed and is either a 17j 500 with a changed bridge or a 19/20j 501 with a swapped rotor and balance. In summary it’s mostly legit but not quite!

The rotor bushings on the entire cal. 49x/50x series were very weak. As a result, many watches have replacement rotor assemblies which don’t necessarily match what was originally there. Obviously this affects the value, but it is important to understand why this happened years ago.
gatorcpa

A 47X rotor will not properly fit as the 47X is 25mm and the 50X is 28mm. 49X is also 28mm (sub seconds)

470-1400R is a fairly common part. So they must have been aware of this weakness. The bushing pinion presses out of the rotor. The sealed packages usually contain both. There is no need to swap the whole rotor, other than lasyness.

A little secret I learned. Many of the common 47x/50x parts are depleted stock and can fetch high prices on eBay. So a search for 490 will often find that variation. Especially with parted out second hand parts which are not in factory packaging. Care does have to be taken as the sub seconds train is slightly different than the sweep seconds one.

These subtle differences are more apparent when one targets lots of unknown or mixed caliber plates.

Yes, these were the packages that contained both the rotor axle and a new rotor pinion (bushing). Really the axle rarely needs replacing, so it's just the pinion that is required, but if you buy just that, you have to ream it to size.


I wouldn't call them weak necessarily. With the weight and inertia of the rotor, it's going to wear just like Rolex axles wear, and ball bearings wear. The entire rotor gets replaced because when these were fairly new watches, no one cared about such details, and the "old timer" watchmakers of the day did the job the quickest way they could, which was to swap out the rotor. When the 550 series came along, Omega offered the entire auto winding unit as an assembly you could just swap out, not because it was weak, but because it was a faster way of fixing the watch.