Rotor scratches on the case-back - how to avoid them

Is it possible your watchmaker does not properly evaluate the rotor when he cleans/ services the movement? @Archer has probably posted pics before showing the wear that occurs at the point of rotation. I believe the watchmaker should be closely inspection for wear damage (and measuring).

Might want to look at your watch maker... It should not start again if the correct parts where replaced and it has been rarely worn or on a winder over 2 years.

Alot here point it out on watches but it could have been from a few services ago.

No way to tell from photos

Strange to have a rotor bearing issue every setvice if fixed properly

Possibly - I often see debris from the rotor scattered all through the movement, contaminating all the lubricant in the jewels. This can lead to premature failure of the lubricant, and I suppose could lead to premature wear of pivots. The rotor can also damage the movement plates if it is flopping around in a significant way.


This is a more complicated answer. It depends on the movement in question and specifically how the rotor is attached.

On the bumper watches, the axle is located on the rotor, and it goes into a jewel - in this case it's usually the axle that is worn, and these are discontinued parts, so is your watchmaker hunting down new parts for these every time they get worn? That's really the only repair here...

For the 55X series style rotor, where the axle is on the automatic bridge and the soft pinion in the rotor is what wears, he should be replacing the pinion and reaming it to size. Here is how it's done:

The old pinion is pressed out, and I use the Horia tool for this:



The pinion is visible here on the underside of the rotor:



Pressing it out:







Here is the new pinion:



I get it started in the rotor:



Then press it in place:



Installed, but not done yet:



The pinion ID comes undersized, and has to be reamed to fit the axle. Omega sells reamers specifically for this operation, and I do this so often I have the reamer and reamer holder set-up in a spare staking set base all the time, ready to go. Oil is applied to the reamer and the hole is reamed out slowly:



I then check the fit with the axle:



Then clean the parts again in the cleaning machine:



And then fully assemble the automatic bridge:



Now here's the thing - if your watchmaker can't get the new pinions, he may be using a rounded punch in a staking set to close up the hole in the worn pinion. This will work for a while, but since the hole would only be closed up at the top and bottom of the length of the pinion, it would have two points of contact and not the full length contact it should have. This means the wear in those areas will happen quickly, and the rotor will get sloppy again in short order. So that's one possible reason why the repairs don't seem to last.

The other could be that if he is replacing the pinion, he might be reaming it out to fit with tapered cutting broaches. These cut larger as you go deeper, so again to get in far enough to make the center of the pinion tube large enough to fit the axle, the top/bottom opening of the pinion tube will be larger assuming they are reaming from both ends of the tube The reamer from omega is a proper straight reamer, with no taper, so it creates a parallel hole and again this gives the most bearing surface.

To give you an idea how close this really needs to be, Omega has 2 reamers for sale, so if the smaller one is too tight on the axle, you then use the bigger one. I have both and the smaller one is 0.702 mm, and the larger one is only 1/1000th of a mm larger at 0.703. So Omega considers 1/1000th of a mm enough difference to create a second reamer for that close of a fit - that's less than 1/2 the diameter of a human hair...

These will wear over time - there's no avoiding that, but doing a proper repair means that the scraping should not be coming back quickly, and you should be able to go 5 years between service without it happening again.

Note that rotors can also be scraping because people who are not able to fix the bushings properly sometimes bend them up so they don't strike the movement plates, and this may cause them to scrape on the case back more easily.

Cheers, Al

This should get a sticky.

I too have seen this in a few Omegas I have gotten and it’s seems to always be the same part. Is this a known common weak link in the Omega design? Do other makers suffer the same problem?

All these designs are a series of compromises. Parts wear, and the softer of the two parts involved is the one that is going to typically require replacing. Wear is a fact of life so for me personally any "weakness" is more about how difficult the replacement of the worn parts is, rather than the design itself.

For example, Chris showed the replacement of the worn axle in the bumper, with the axle riveted in place - this is similar to how Rolex axles are done. Repeated replacing of the axle can leave the hole it has to be riveted into large, so that's one potential concern. For the Omega with the soft bushing that I showed, to me that is a better design - easy and quick to replace - if I wasn't taking photos it would literally be a 3 minute job.

Sometimes the axles on the 55X series can fail, but not usually from wear - it's usually something like this - notice the line at the base of the axle:



It's a crack:



Now I had serviced this very watch about 7 years ago, and I went back through the photos and I can clearly see there was no crack in the axle base at that time, so something happened in the time since the last service to cause this. Most likely a large shock of some kind, so even though the pinion is the part that is replaced, you still have to check the other parts as well. in the bumpers you need to check the jewel that the axle goes into - I do find they can get broken fairly easily compared to the damage to the axle here seen above.

Note that cracks can also show up in other places, such as the rotor itself. Here's a Rolex rotor that is cracked in a couple of places - I've seen a number of Rolex watches cross my bench with cracked rotors:



This one someone had tried to repair, but it wasn't done well:



Here's another example:



Many brands have gone to a ball bearing, but those can also wear. This is an ETA 2824-2 in Tag, and you can see the slop in the bearing before I replaced it, and how much tighter it is after:


The 2824-2 bearing presses in and out of the rotor, but many bearings are held in using a locking ring, and changing the bearing is quite easy. Here's an Omega 1120 that needs a new bearing:



The rotor is placed into the holder, and there are teeth in the holder that match the teeth on the back side of the bearing to hold it in place:



The red tool has prongs on it that are used to turn the locking ring:



Locking ring is removed:



Rotor is lifted off:



New bearing is placed into the holder, rotor is placed back on, and the locking ring installed using the red tool again:



Again this just takes a few minutes:



Now there are designs that are not the best for this - for example the F. Piguet based watches that Omega used have the bearing for the rotor installed into the bridge, and the bearing can't be bought separately, so when the bearing wears out the entire bridge has to be replaced - that is a much more expensive repair than just changing the bearing:



Omega's versions of the 7750 are similar - the bearing is burnished into the rotor so to replace it you have to replace the rotor:



In contrast the regular 7750 series uses the locking ring design that I showed for the 1120, so not sure why Omega made this change on the 1150/1160 series movements that are 7750 based. Same applies to the 3330 by the way...I do want to figure out a way to replace this bearing at some point, but so far haven't had time to do so...

Speaking of 7750 based watches, I've seen rotors fail in other ways too...



In this case the sintered tungsten weight section came loose from the flat plate portion of the rotor...

In the standard textbook for watchmaking schools The Theory of Horology, it states that a reversing wheel in the automatic winding system of a watch can change directions as many as 10 million times per year - this means the rotor is also changing directions that many times. The automatic winding portion of a watch is one of the hardest working parts inside the watch, and it can be wearing without having any immediate effect on the timekeeping of the watch. This is why when people say as long as your watch is keeping good time it must be okay, well they just don't understand the technical side of watches very well.

In watches where the parts are discontinued or hard to get, letting the watch go until you see a problem is not a good idea...so regular service is the key.

Hope this helps.

Cheers, Al

Wow!!! That was a total crash course in rotor 101!!

Isn't one of the major reasons vintage Omega, Rolex, etc didn't use ball bearings is that Eterna held the patent for the design?