AC 4-pole synchronous motor lubrication

[Dimani4]

Hi people,

Recently I got sharp-rp11h turntable. I changed the belt but anyway the RPM was still low. I took the whole turntable to some guy to check the belt in place. But he looked at this turntable and said right away that this belt is good and the problem of some regulator. So I took it home to see which regulator is the problem. So meanwhile I dissected the motor because this motor wasnt in service for a long time. The motor is 4-pole synchronous AC motor which runs at 1500 RPM at 50Hz. So look here:

And the spindle which is actually spins:

You see here the upper plate. The upper plate goes up on the motor spindle at the longest part of spindle. Here you see the tiny hole written "Oil". So its understood I need to drop there the oil. I drop oil into this hole and the oil will come down to the big hole where the spindle comes out. The question is should I put the oil as well into the lower plate where the short part of the spindle comes in?

Here the assembly of all these parts together:

Thank you.

 

[Echo]

Hi people,

Recently I got sharp-rp11h turntable. I changed the belt but anyway the RPM was still low. I took the whole turntable to some guy to check the belt in place. But he looked at this turntable and said right away that this belt is good and the problem of some regulator. So I took it home to see which regulator is the problem. So meanwhile I dissected the motor because this motor wasnt in service for a long time. The motor is 4-pole synchronous AC motor which runs at 1500 RPM at 50Hz. So look here:
View attachment 1534

And the spindle which is actually spins:
View attachment 1535

You see here the upper plate. The upper plate goes up on the motor spindle at the longest part of spindle. Here yo
[...]

Yes, you should oil both bearing points on this type of motor. The upper bearing (where the longer part of the spindle sits) has that dedicated oil hole for a reason, and a drop or two of light machine oil there is correct. The lower bearing, where the shorter stub of the spindle sits, should also receive a small amount of oil. Both ends of the spindle run in bushings or sleeve bearings, and if either one is dry it will create friction and drag the motor down below its rated speed.

For the oil itself, use a light, non-detergent machine oil or a purpose-made turntable/motor oil (such as Nye or a sewing machine oil). Avoid anything too thick, like WD-40 (which is not really a lubricant) or heavy grease. One or two drops per bearing is enough; over-oiling can attract dust and cause its own problems, and excess oil can migrate onto the rotor or stator.

Once you have lubricated both bearings, reassemble the motor and let it run for a few minutes before measuring the speed. If the RPM is still low after lubrication, then the issue the technician mentioned - a regulator or speed-control component - is likely still the culprit and worth investigating separately, but stuck or dry bearings are a very common cause of low speed on a motor that has sat unused for a long time, so this is the right place to start.

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