Beogram 400x DC Platter Motor Restoration Marathon

I recently received four DC platter motors from Sonavor for restoration. He needed them for a bunch of Beogram 400x restorations. Let the motor marathon begin! This shows the four motors:

In the following I only show the process for one of them. The first step is to take the motor apart to get the bearings out:

The bearings are the two small donuts on the black pad. The next step is to immerse them in motor oil and pull a vacuum:

If the bearings are in need of oil replenishment, the vacuum extracts the air from the pores of the bearing material. This manifests itself as bubbling from the bearings. After 1-3 days the bubbling stops and then it is time to extract the bearings: 

Then the motor is put back together and it is time for a RPM stability test with the BeoloverRPM device:

The BeoloverRPM allows logging the RPM over extended periods of time. I usually measure for about 24 hrs. These are the curves I measured for the four motors:

They are all pretty similar and show some small RPM drifts over time, which are most likely related to temperature changes in the circuit and its surroundings. The fourth (blue curve) is a bit more unruly. I get this sometimes. I have seen in the past that such motors 'quiet down' after they run for a while. Not sure why some motors behave like this. At any rate, the variations are much too small that they would be audible. The joys of analog audio! These motors are ready for duty again!