Beogram 4002 DC Motor Restoration

This post reports about the restoration of the 2nd Beogram 4002 DC motor (1st: see here) that recently arrived from the UK. This shows the motor as received:

I took the motor apart to extract the bearings for oil infusion:

The bearings are the two small brass donuts on the black pad up front. I immersed them in oil and pulled a vacuum. Immediately, vigorous bubbling started:

This indicated that the air was drawn from the porous Oilite bearing material making room for fresh oil to diffuse into the bearing. After about 48 hrs the bubbling stopped and I extracted the bearings from the oil:

I reassembled the motor and installed it into one of my Beogram 4002s. I ran it for 24 hrs measuring the RPM in 10s intervals with my BeoloverRPM device. This is the curve that was measured:

This is a pretty good result, but this motor seems to have slightly more variation than the first one. It is very likely that it will 'calm down' after it runs for some more time. The root cause for this kind of behavior may be that the orientation of the bearings improves over time as the motor runs. See here for a documented case, where the improvement happened over three weeks of running the motor. The joys of analog audio!...;-)