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!...;-)

Beogram 4002 DC Motor Restoration

Two Beogram 4002 DC platter motors arrived from the UK. This post reports about restoring the first one. This shows the motor as received:

I disassembled the motor to get the bearings out:

The bearings are the two small donuts on the black pad upfront. These bearings are made from a porous material ("Oilite"), which has a limited amount of Oil infused when new. Over time this oil leaches out lubricating the shaft. When the oil is gone the shaft runs dry, which seems to be the case with most Beogram 400x motors these days.

I immersed the bearings in motor oil and pulled a vacuum:

Immediately, vigorous bubbling started. This is a sign of the air drawn out from the pores by the vacuum. Once the air leaves, the volume is filled with oil that diffuses into the material to replace the air ("nature abhors a vacuum"...;-). After about three days the bubbling came to an end and I assembled the motor for testing. 

I installed it in one of my Beogram 4002s and ran it for 24 hrs while monitoring the RPM every 10s with my BeoloverRPM device.

This is the curve I measured:

That is as good as it gets. This motor is ready for duty again!