Overhaul of the Thorens TD 124 motor

Please note: Information described in my webpages is to the best of my knowledge, but I cannot guarantee the information is entirely correct and I am not responsible for any consequences of using the information.

Unsolder the wiring connections, and remove the motor assembly from the chassis.

Disassemble the motor. This is the inside view of the bottom over.

Drill out the rivets (with a 2.5mm diameter drill).

Remove the bearing holder.

The felt rings have hardened with age and no longer retain oil. They should be renewed.

Remove the thrust plate holder.

Inside of the upper cover.

Remove the bearing holder.

These felt rings have hardened, too.

The rotor.

The bearing ball in the lower end of the rotor.

The bearings.

(The wire threaded in the right one is for identification.)

These are oil-impregnated bearings. They are made of sintered metal and retain oil.

Heat the bearings in an oven.

Old oil contained in the bearing will exude.

Immerse the bearings in new oil.

The following is a suggestion from Mr. Peter Folwer. I agree with his ideas. Thanks Pete!

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Another thought about cleaning the sintered bronze motor bushings - I was considering trying a repeating cycle of your recommended heating in an oven to more completely flush the old oil out of the pores. Perhaps something like:

1. Heat at 250 degree F on paper towel for 20 (?) minutes
2. Remove, wipe with a lint free cloth and drop in solvent to dissolve old oil.
3. Wipe off solvent and back in oven. Repeat until no further old oil is obtained.

Then to flush out the solvent and load the bushing with oil:
4. Heat in hot oil.
5. Remove and wipe off oil with lint free cloth. Allow to cool and then heat in oil again. Repeat several times
to flush the solvent and replace with clean oil (most solvents are volatile at high temps so one or two times may be sufficient).
6. For the final oiling, leave the bushings in the oil and allow it to cool - they will retain the maximum oil

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Prepare (fabricate) new felt rings.

Use a pair of M2.6 screws/nuts instead of rivets.

If the thrust plate (a small nylon plate) is dented, it could be reused by turning it upside down.

The bearing is retained by the spring plate. The plate determines the position of the bearing.

The bearing can be moved (tilted) slightly in the plate, and in theory, due to their hemispherical shapes (of the bearing and the spring plate) it is self-aligned. But, in reality, you may have to adjust it slightly by yourself.

The spring plate is sandwiched by the felt rings (felt pads).

The bearing is oil-impregnated, but needs to be supplied with oil for continuous use. The felt rings act as a reservoir, and retain oil and supply the bearing with oil.

Apply enough oil to the felt rings before assembly.

The thrust plate and its holder are thoroughly cleaned.

The bearing holders in place.

These are the upper cover and posts salvaged from a junk motor of TD 124 Mk-II..

The posts are extended and rubber bushings can be doubled.
They make some improvement in isolation of motor vibration.

Reassemble of the motor is the most important and most difficult part of the overhaul.

Correct alignment of the upper and lower bearings is the key to success.

(I have not yet found the definitive and most effective ways of aligning the bearings, though...)

Check it by rotating the rotor shaft by hand. It should rotate freely and smoothly.

Supply AC mains voltage to the Red leads.

Connect the Black leads each other for 100 - 120V ; Yellow ones for 125 - 150V ; Green ones for 220 - 250V. (And one of the Green leads goes to neon bulb via a resistor.)

Ideally, run the motor with low voltage at first by using a voltage regulator, and raise the voltage gradually.

Check noises and vibrations carefully. Hold the motor correctly (horizontally) as same as it is used in the chassis while checking it.

Bring your ear close to the motor, and also try to feel vibrations with your hand.

If noises (rattles) are excessive, try to realign the bearings.

With a use of voltage regulator, the voltage at which the motor shaft starts rotating is an indication of a good (or bad) alignment. Lower the voltage is, better the bearing alignment is.

Also, the time (how many seconds) the motor keep running after the voltage is shut off is another indication. Longer the time is, better the alignment is.

The left photo shows a stethoscope (this particular one is for a mechanic) is quite useful for checking noise.

If noise check is OK, perform a break-in (preferably, with low voltage first).

Overhauled motor is likely to get very hot for a while.

I have experienced that the difference of motor speed when it is cold and when it gets hot is more noticeable in a break-in period.

Also please note, when the motor and other parts are back in the place, lateral force and load are put on the motor spindle/bearings by the rubber belt. So, it may need some more break-in time for the motor to begin running in the best condition.

The following is another suggestion from Pete. I completely agree with his ideas. Thanks again.

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I believe the information on your website is quite good, and only needs additional considerations in the alignment section. Your advice is excellent for preliminary alignment and will help the reader avoid accidental damage to the motor.

Here are some additional ideas to consider:

I think the final adjustment of the motor top and bottom plates should be done with the motor installed in the turntable with the belt attached, the platter installed and the motor running. This will put the proper load on the rotor shaft and ensure quiet operation under load.

Since the motor runs hot, I also think it should be allowed to run for at least half an hour before alignment since the different metal parts will expand and contract due to the heat. I found my motor would be almost silent at start-up but after warming up it would become audible again. Unfortunately, this means wearing cotton gloves for protection from the hot motor while working.

I also found a stethoscope was the best way to hear the various motor noises, but my hearing is not so good any more! ;-)

I characterize the sounds the motor makes into 3 types - electrical (hum), normal bearing to rotor contact (whirring) and misaligned end-plates (grinding or rubbing). When aligning the motor I seek to eliminate the grinding/rubbing noise completely and minimize the whirring. Electrical hum is unavoidable.

I also assume that minimal noise translates into minimal vibration, but this may not be true if the rotor is not balanced or centered on the shaft properly. I have no suggestions for correcting either problem if present.

The alignment process I follow is like this:

1. Place the TT where you can access under the motor with both hands safely while the motor is running.
2. Assemble the TT completely (belt, platter and mat).
3. Loosen the 4 motor screws so that the top and bottom plates can move only with firm effort.
4. Turn the motor on and allow it to run for 1/2 hour or longer.
5. Wear cotton gloves to proctect your hands from the hot motor.
6. Using the stethoscope, gently move the top and bottom plates slightly to develop an understanding of how the sounds change as the plates move relative to each other. I find it takes little time to find an alignment where there is no grinding/rubbing sound and very little whirring. This is the ideal alignment.
7. Carefully begin tightening the motor screws in a cross pattern, using 1/4 turns to tighten around the pattern. Listen for changes in the sound of the motor. Overtightening one screw before the others can cause misalignment from unequal torque on the end plates.
8. At some point you will find a particular screw cannot be tightened any further without making the whirring or grinding noises worse. Stop adjusting that screw and continue tightening the rest as before. Periodically check bacl to see if the noisy screw can be tightened further. Sometimes it may and sometimes not.
9. For my motor I ended with 2 screws fully tight, one screw 80% tight and one at 60%. This alignment is now over one year old and is still silent after the motor is hot, so I think it is not critical for all screws to be 100%.
10. The next time you start the motor it may be quite noisy until it comes up to full operating temp. Then it should be whisper quiet and stay that way.

Those are my thoughts and experiences. I hope some of them may be helpful for you. Please feel free to include any of the above on your website if you feel it is useful.

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