Beogram 4002: DC Platter Motor Restoration

I recently received the DC platter motor of a Beogram 4002 from a customer in Utah for restoration. Most Beogram 400x platter motors have dry bearings these days, and that usually results in intermittent RPM variations that get increasingly worse. Re-infusion of the bearings with oil is the cure for this issue.

This shows the motor as received:

I took it apart to get to the bearings:

The bearings are the two small donuts on the black pad upfront. I immersed them in motor oil and pulled a vacuum. Immediately strong bubbling started:

This bubbling is indicative of air being drawn from the empty pores of the Oilite bearing material. Once the air leaves, the remaining vacuum allows oil to diffuse into the material. The process usually takes about 2-3 days until the bubbling stops. Then it is time to extract the bearings:

I re-assembled the motor and then it was time to give it a 24 hrs RPM stability test with the BeoloverRPM device:

The BeoloverRPM allows logging the RPM for extended periods of time in 10s intervals, perfect for spotting intermittent RPM inconsistencies. This is the curve I measured after about 24 hrs:

In terms of short term variations this curve is as good as it gets with the Beogram DC platte motors. The long-term drift is a sign for bearing and shaft 'getting used to each other' in their new orientations after the infusion process. The RPM will stabilize in a few 10s of hours. Until then it is a good idea to check the RPM periodically to make sure the speed is close to spec.