Monday, March 13, 2017

Beogram 4000: Restoration of AC Motor

A while ago I realized that the AC motor of the Beogram 4000 that I restored started making distinct knocking noises in sync with the pulley rotation when I played it. This was a sign that the Oilite brass bearing needed an oil re-infusion. Oilite bearings are porous brass bearings that get factory oil infused under vacuum. Over time the oil is dispensed onto the shaft of the motor and from there into the motor housing. This means that after a certain run time the bearings need to be replaced or re-infused. If you have a food vacuum sealer, this can be done with a mason jar. Here are a few impressions of my process:

First the motor needs to be removed
Then the two rivets that hold it together need to be pressed or drilled out:
This shows the motor opened up:
and a peek at the bearing in the bottom part:
For the record, this shows the arrangement of a spring and washers on the motor shaft:
Since after removal of the coils there is only metal left, one can simply put the entire enclosure into oil and pull a vacuum:
The usual air bubbles formed as the air escaped the brass pores. After about 24 hrs the process came to a halt, indicating that the bearings were again full of oil.

Since the rivets had to be destroyed for opening the motor, I replaced them with two 3D printed parts that hold M3 nuts enabling to put the pitch adjustment screws back in:
This shows the motor back in the enclosure:
After this procedure the motor was quiet again.

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