The TD124 Motor
My example came with a spare motor. The original TD124 motor is seen to the right of the turntable. The PO had trouble with too-fast running speeds and had replaced the motor with another. Unfortunately the fast running speeds persisted. For this page I will clean and lube the original motor to see if it can be re-used.
The motor type is a shaded pole induction motor. In the above photo the two phase coils are visible on either side of the large central opening. The different colored wires are for different operating voltages. Black for 100-120. Yellow for 125-150. Green for 220-250 volts. The red wires are for AC mains.
Looking inside the casings after many, many years of use and then many years of non-use. The lube reserve held within the felts has dried and turned to wax.
The bushings are contained within an assembly of felt pads, spring collar and cover. These are originally held in place with hollow rivets. To service the bushings the rivets were drilled out. I've seen photos of these motors far more gunked-up than this one was.
Take a look at the bottom end cap with the white plastic thrust pad. The small bearing ball rides between the pad and the countersink within the end of the rotor shaft. Wear is indicated by the indentation within the white pad.
Some of the parts. The white plated parts were allowed to soak in Berryman's B9 Carburetor cleaner. After 1/2 hour they came out free of crud and shiny. The carb cleaner can also strip paint. Caution is in order. Caustic skin irritant, eye melting acids! The bronze spring retainers were simply washed in lacquer thinner and wiped dry. On second thought, these could have also benefited from a soak in the carb cleaner, but they will be functional as is.
The sintered bronze bushings after the first cleaning. First the bushings were baked at 250 deg. F. A dark greasy substance oozed out. Following that they were washed in a jar filled with lacquer thinner then allowed to dry. Next I put the bushings back in the oven just to see if any more crud might run out. It did. More black ooze. Another cleaning with lacquer thinner, then allowed to dry. Next I placed the bushings in a container of lube and put this into the oven at 250F. After several minutes they were removed from the oven and allowed to cool while still submerged in the lube. Next I removed the bushings from the tin filled with lube and then placed them in a disposable pie tin to be baked dry at 250F. No more black ooze. Once more the bushings were put in a container filled with fresh lube and baked at 250F for a few minutes, then removed and allowed to cool. Now they were ready to be installed. the lube being used is 20 wt turbine oil. ( I'm using Texaco R&O 46).
Note the spherical ends. This feature makes possible a limited amount of alignment adjustment between the upper and lower casings once all of the parts are assembled.
Oil reserve felt pads: These I lightly cleaned by soaking/washing in a lacquer thinner bath, then allowed them to dry. This was followed by filling the pads with 20 wt turbine oil to the point where the pads were fully saturated with the lube.
Bearing end cap, thrust pad and ball, after cleaning. The end cap went into the carb cleaner. The ball and pad were simply wiped clean with a paper towel. The bearing ball mic's at 2mm in diameter. The pad measures 1mm thick.
Without the ball. The previously used indented side is now faced down. The unused side provides a flat new surface to engage the thrust ball. I'll try it this way for now. Perhaps, later on, a heavy bronze end cap with a fresh Delrin thrust pad could be made for this! I'll put that idea on the back burner for something to try at a later date. Also, the bearing ball could be replaced with another one of different material.
The lower bushing after a few cleaning and lube cycles. It awaits to be inserted into the spherical socket of the end case. The end cap with thrust pad is positioned to receive using m2.5 x .45 machine screws The larger oil retaining sponge pad is laid against the end case.
The bushing is inserted with its spherical end fitted within the spherical socket of the end case.
The inner cap is partially assembled with the smaller sponge pad and the bronze bush retainer spring. it is ready to be fitted over the bushing end and onto the case.
After fastening the bearing assembly onto the lower case. The inner cap tensions the bushing while allowing the bushing to be rotated a small amount within its spherical socket fitting. The m2.5 hex jam nuts were carefully ,and somewhat tediously, fitted with my fingers to engage the threads of the machine screws. Once the nuts had a 'start' on the threads I used a screw driver to engage the slotted end of the screw while holding the hex nut with a small plier. In this way I was able to tighten the assembled bushing quite firmly to its end case. Do note that the spherical end of the bushing must not be locked into position. It must be able to swivel within its assembly. Test this by placing the rotor shaft in the bushing and manipulate the bushing attitude using the leverage of the rotor shaft. If the bushing puts up too much resistance there is something within the assembly that is wrong.
The bushing assembly is installed to the upper case the same as the lower but with the exception that there is no end cap. The rotor shaft fits through the upper case. Like the lower case, it is important to insure that the upper bushing can be swiveled within its mount.
The importance of the swivel mountings is for aligning the rotor shaft to the bushings. Ideally, upon assembly, the rotor will spin within the upper and lower bushings only touching a film of oil and not making hard contact with any part of the bushings themselves.
Another view of the end cases after cleaning and reassembly of the bushings.
The thrust ball, in my example, is magnetized and sticks itself to the end of the rotor shaft. Very handy for assembly and disassembly. Failing the magnetism, a small dab of grease may be used to retain the 2mm bearing ball into the countersink end of the rotor shaft during assembly.
Above three photos: To assemble the motor I fitted the rotor (with thrust ball stuck within the c-sink at end of the shaft) into the bushing of the lower case. Then the stator core was slipped over, then the upper case. Care was taken to align the wire harness and fit it through the intended port of the upper case. Note the photo showing the position of the posts. these fit up through the cast chassis for mounting and must be oriented as shown.
Btw, the motor in the above photo is not yet fully assembled but is complete enough to make preliminary bushing alignment adjustments.
Before installing the motor to the chassis. And before applying electricity to the motor. With the four assembly bolts not yet tightened, slightly loose. Hold the assembled motor in one hand. With the other hand hold the top of the rotor shaft between thumb and forefinger. Wiggle the shaft back and forth, around and forth, to operate the self aligning bushings within the upper and lower casings in an operation designed to align bushings upper and lower to the rotor shaft. Then, spin the rotor shaft by giving a spin with the thumb/forefinger hand. Observe how long the rotor spins. Repeat this process until the longest spin-down time is achieved.
After the preliminary bushing alignments you may install the assembled (but not yet fully tightened) motor into the td124 chassis.
Next: After the motor has been installed to the turntable, and the belt has been fitted, and while the motor is running and fully warmed up, under load, I will make further bushing alignment adjustments using the stethoscope.
For this operation I have constructed an assembly jig to hold the chassis while working on various parts of the turntable. It will be useful to allow access underneath the chassis and to the motor while making the following adjustments. Also for this operation the motor is powered up. I use an isolated power source with adjustable voltage output. (Viz ISOTAP WP-28) Do be careful not to shock yourself. Voltage level is in the range of 110-120 vac and can be lethal. (as in this is enough voltage to kill people)
The 4 fasteners that hold the motor assembly together are still loose so that the upper and lower bushing cases can be manipulated for position. A small, light piece of hardwood is used to gently tap on the upper and lower motor casings in order to slightly adjust their positions relative to one another. The stethoscope is the instrument that will allow us to know if the adjustment was good or not good by the noise level that results from the adjustment.
When re-tightening the 4 fasteners it is observed that the adjustment is altered. This I can tell by listening with the stethoscope. So then further adjustments are made to the upper and lower case position while the case is being tightened. This is a painstaking process. The reward for going to this trouble is a quieter running motor, and drive train that comes up to speed on the strobe within 1 minute of a cold start-up...and then holds a constant speed all day long. A rock steady strobe observation.
The next process is to run the motor and drive train components in by playing records. You may put the assembled chassis in its plinth for this operation. Typically I will play records for a week.
After this process the motor should now spin freer than before. It should come up to speed sooner than before and be ready for long term operation.