2078 E50
TD124 Motor refurbish details
Disassembly:
The motor assembly after having been removed from the chassis with wiring
harness intact. There is no need to de-solder anything!
Measures and observations
The rotor shaft shows some evidence of having been in operation for
approximately one half of a century.
The rotor shaft has been wiped down with a clean rag. A micrometer reading
of the shaft diameter was .1867 to .1865 inches.
the thrust bearing ball is being held into the countersink at the shaft end by a
bit of grease.
and the grease is approximately one half of a century old. It has
hardened. Turned to wax.
the disassembled pieces. Note that the mounting shaft on the upper motor
case has been removed and is now ready to accept MKII mounting shafts.
Clean-up.
Rotor and shaft: The rotor was thoroughly bathed and wiped down in acetone. The shaft areas that were in bushing contact are now much less visible. The rotor shaft diameter, after initial cleaning, measured .1867 to .1865, depending on the area being measured. After a more thorough acetone bath, readings were .1865 uniformly from one end to the other with circularity (roundness) deviating less than .0001 inches. My assessment is that there was a thin hardened layer of lubrication residue build-up and this has been removed.
The rest: The individual parts, casings, retainers, etc which will be reused have been cleaned/scrubbed in acetone to remove decades of accumulated grime.
Assembly
New E50 motor bushings have been cnc machined out of Oilite Bronze to replace
the original 50 year old bushings. The Oilite material is the same as the
original. Oilite bronze is a product name for a material also known as
sintered bronze. This particular type of bronze is highly porous, allowing
lubrication to be retained within the bushing, providing a constant supply of
lubrication to the rotating part. The bronze is very soft and tends
to wear far quicker than does the shaft which rotates within it. Two bushings from this new lot will go into this project motor.
In the photo are the cleaned parts and some of the new replacement parts ready to go in. New oil
retaining felts. New Oilite bushings (In the container of lubrication),
will replace the old ones. Note also the container of Loctite thread
locker. The thread locker will be used sparingly on the machine bolts and
nuts to ensure that the bushing assembly does not vibrate loose.
A new bearing thrust pad has been cut. The new pad material is Delrin infused with
Teflon. This Delrin/Teflon blend retains the sonic signature of plain
Delrin but with a greater wear life. Plastics have come a long way since
1957 when the TD124 was originally introduced to the world.
In this photo the lower motor case is partially assembled. The lower cap with the thrust
pad is beneath and being located by the two machine bolts. Visible are the
new oil
retaining felts after having been soaked in Texaco R&O 46 (turbine oil 20
wt). The felts will feed lubrication into the porous bronze bushing over
time to maintain a continuous supply of lubrication to the rotor shaft for
another 50 years. In this shot the assembly awaits the placement of the
upper retaining cap Fastener thread size is M2.5.
The cleaned rotor shaft and its new thrust bearing.
The original hardened steel ball bearing thrust has been replaced with this new
silicon nitride ceramic bearing ball. Size is 2mm. The new bearing ball features a surface
which, unlike steel, completely lacks porosity. Meaning improved surface smoothness. Meaning
less friction.
With a dab of bearing grease, the new bearing ball is held within the
countersink of the rotor shaft end. Ready for assembly to the motor case.
The motor is assembled. In this shot it can be seen that the original
mounting shafts have been replaced/upgraded with the MKII length shafts.
It is to be
fitted with a double grommet arrangement as per the TD124 mkII. The sonic benefits of
this upgrade is significant and should be carried out to all original TD124
(mk1) players.
Here's a side by side shot of the motor assembly before and after the upgrade/renewal.
preliminary bushing/shaft alignments. The motor bushings are of a self-aligning
design. It is necessary for the upper and lower bushing to share the same
axis of alignment so that the rotor shaft may operate with the least amount of
contact with bushing walls.
The adjust; the upper and lower motor casings are gently moved (tapped) with a light/soft mallet into a position of relative alignment with each other. To gage the success or failure of each adjustment, the rotor is spun and observed for the amount of time it spins freely before slowing to a stop. Longest spin time is desirable. During this process, the case fasteners are only lightly snugged down in order to allow the upper and lower case shells to be easily shifted for position. Once best alignment is achieved by this method, the 4 case fasteners are lightly tightened in an order that is least likely to alter the adjustments already made. After tightening the rotor is spun again to check for free spin.
assemble the motor to the chassis and begin making bearing to shaft alignments for optimal motor operation.
After initial upper and lower bushing alignments, the motor was run steady, 24 hours/day, for one solid week. Then the motor was observed for vibration as follows:
using a mechanic's stethoscope, the motor is listened to at various points on
the outer motor body. On the lower case, on the upper case, on the plates
in the center.
The 4 fasteners that hold the motor assembly together are loosened so that the
upper and lower bushing cases can be manipulated for position again. 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.