The Omega 550 series of movements is a common series of movements from the 1970's and was put in a huge variety of Omega watches. It's a great movement and I love working on them, but like all things it isn't without its issues. The oscillating weight axle is made of steel, but the pinion that it rotates in is brass. The brass pinion wears and needs to be replaced. Thankfully, the pinion is a spare part that is still available from Omega and can be replaced.
Below we can see the oscillating weight and bridges assembled on the main-plate.
You can see that the oscillating weight (rotor) is touching the main-plate and will be touching the caseback when the watch is turned upside down.
When I put pressure on the rotor the slack is taken up, showing where the oscillating weight should be sitting.
The new pinion ready to install.
We use the hora tool to press out the old friction fit pinion.
With the old pinion removed we seat the new pinion ready to install.
The pinion is pressed in with the hora tool.
The new pinions are supplied under sized and need to be reamed out to fit the axle.
We further ream out the pinion.
The new pinion is now installed into the oscillating weight and put onto the axle. You can see the distance between the oscillating weight and the main-plate, there is clearance there and the weight will no longer rub on the caseback or the main-plate.