Grundig TK120 motor troubles

[martin.m]

Are the motors in these machines meant to be lubricated? I had one that was stiff to turn so took apart, cleaned and oiled the spindle at both ends. The machine worked fine for a few days, but after not been in use for a week the motor has become stiff to turn again. I used some very fine clock oil. The stiffness was in the bottom bearing. On reassembly, I had to centralise the rotor using shims cut from a piece of thick paper to stop it from scuffing against the motor body. I thought this one would be a quick fix, any advice greatly appreciated.

[DMcMahon]

Not much help here but attached is the lubrication information from the TK 120 Service Manual. No explanation of the Fig 5 symbols.

David

[oldbury863]

I have worked on a few of these machines but I cannot help regarding your requirement to use paper shims. Certainly the holes in the laminations are larger than neccessary and require the bearings to be aligned manually as there are no locating lugs. Have you completely removed the rotor and cleaned the shaft of dried up oil? I suspect that the oil you have used is not suitable as the motor's running temperature is much higher than typically found in a clock! I previously used a general purpose Starret oil on the syncronous motors fitted to chart recorders and found it most unsuitable. It rapidly dries out when exposed to higher temperatures. I have however had success using modern car engine oil. I have lubricated the phosphor bronze bearings of my gas boiler fan unit with engine oil a couple of times now and it still performs well after 21 years of use.
Richard

[mitajohn]

In order to center the rotor you have to use two flexible bronze filers about 0.30 mm thin each, as in the pic. Build them.

[martin.m]

Thank you for your replies. I spent an afternoon experimenting with a couple of these motors. Richard, I think you are correct regarding the clock oil. I used a drop of car engine oil and got much better results. John, thanks for the advice about the shims. I used strips of good quality (thicker than usual) writing paper to centralise the rotor. If the clearance is wrong, the motor will spin when turned by hand but when mains is applied will just sit there and vibrate. In the Grundig TK120 range of machines, the 250v HT and 6.3v heater supplies come from windings on the motor. It saves a lot of time if mains is applied for a quick test before fitting the motor back into the machine, The primary windings need to be connected in series for 240v operation of course. I think that in today's trendy speak, this has been a Learning Curve.