Beogram 4004: DC Platter Motor Restoration

Sonavor recently sent me a Beogram 4004 DC platter motor, which will be used in one of his Beogram restoration projects. This shows the motor as received:

I disassembled the motor to extract the bearings for oil infusion:

The bearings are the two small donuts upfront on the black pad.

I immersed them in motor oil and pulled a vacuum. Immediately strong bubbling started:

After about 72 hrs the bubbling stopped and I extracted the bearings from the oil:

Then I assembled the motor and ran a 24 hrs RPM stability test with the BeoloverRPM device, which allows logging the RPM for extended periods of time in 10s intervals:

This is the curve I measured:

There are some slight fluctuations, which is seen in some of these DC motors after the oil infusion process. My working hypothesis is that in such cases the bearing surface is polishing itself as the motor drives the platter. I try to install the upper bearing in the same orientation as before, but of course there are small variations - after all a human is doing it...;-), and I think that causes some friction fluctuations. In my experience this phenomenon gets better over time as the turntable is used. At any rate these RPM variations are much smaller than what the human ear can detect, i.e. this motor can be used again!