Beogram 4002 (5514): Rebuilding a Noisy DC Motor with Oil Infused Bearings

Most Beogram 4002 with DC motor need the motor rebuilt at this point in time. Sudden RPM drops or a noisy motor performance are signs that the time has come. In this particular Beogram 4002 (5514) the motor was fairly noisy when running without load. I rebuild all DC motors when I restore a 4002 since these problems will sooner or later hit all of these motors. The main cause for these performance issues are drained oil infused brass sleeve bearings with 'permanent' lubrication. these bearings are made from porous brass, which are infused with oil under vacuum. This type of bearing is good for many years until the infused oil runs out. While the motor is running the infused oil continuously replenishes the oil film on the bearing surface. The spinning shaft slowly distributes the oil to locations outside of the bearing, eventually depleting the oil.

Since such low voltage DC motors with appropriate inductive tacho control feedback appear to have vanished from the marketplace, the only solution is to replenish these bearings with oil to give the motor another lease on life. The extraction of the bearings requires a complete disassembly of the motor. Otherwise it is not possible to get the bearings back in properly. This shows the motor disassembled. The bearings are the two small round items in the 'front row':

Once I had the bearings out I immersed them in a mason jar and pulled a vacuum with a FoodSaver pump. Immediately, air bubble started emerging from the bearing indicting that the infusion process had started:

After 24 hrs the process had abated and no more bubbles could be noticed:

I read that about 20% of the weight of such a bearing is the infused oil.

I extracted the bearings from the jar and reinstalled them. This shows the bottom bearing installed in the brushes carrier:

The top bearing needs to be installed by clamping the holding ring down on the spring that holds the bearing in place. This shows the bearing with the spring:

After slightly bending the tabs of the holding ring,

I used my special tool with adjustable pliers to clamp the tabs fully down:

This ensures that the bearing is held in place snugly as it was before disassembling the motor.

Then I put the motor back together:

After soldering the PCB back on it was time for a test with my bench supply:

A properly assembled motor should draw less than 30mA at 5V. If the current is higher the brush career plate needs to be loosened and the screws carefully tightened in several small steps in sequence around the motor (as you would tighten a vacuum flange).

These motors are very sensitive to improper alignment of the shaft with the bearings and they will not run well if this is not done properly. Another frequently encountered issue is that the motor runs in the wrong direction after assembly (or it runs not at all). This is caused by the brush carrier plate being mounted at the wrong angle relative to the permanent magnets in the motor. If that happens remove the screws, rotate the bottom plate by 120deg and try again. If it still not works properly, do another 120 deg and then it should run int he right direction. Generally, it is a great idea to make an alignment mark with a Sharpie pen before taking the motor apart...;-).

Alright, it seems this motor is running well again...the grinding/screeching noise went away. I will give it a RPM test with my BeoloverRPM device after I rebuild the main PCB with a new RPM relay and RPM trimmers. These items are the other leading trouble spots causing unstable RPM performance of DC motor Beogram 4002s.