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TELECHRON ROTOR
Rejuvenation...
By Dr. Radio
When the encapsulated rotor assemblies were attached to the Telechron clock and timer units that left the Ashland, MA plant, they certainly didn't lack quality, however, they did lack adequate lubrication! This article focuses on some tips and tricks to get them running quietly and effectively again. This is simply a guide, no gurantees expressed or implied (i.e. your results may vary!). Please read all the information carefully before attempting the procedure on your own.
The vast majority of "baby-boom era" clock-radios utilized a Telechron Timer as the motoviation behind the familiar clock dial. While the timer internals are fairly straight-forward and reliable, the rotor capsules (referred to simply as rotors) are the most notorious for noisy, sluggish or erratic behavior in time-keeping. The rotors are the driving force that transforms magnetic field (created by the alternating current from your wall outlet by the coil) to mechanical motion needed to run the works. When the mechanicals inside the rotors were assembled, only a small amount (roughly a few cubic centimeters or less) of oil were dispersed inside. Fine machine oil was apparently utilized. Unfortuantely, the lubrication was deemed adequate because the following was assumed:
1) There would be enough oil on gears, shafts and bushings upon assembly thanks to internal capilliary plates designed to hold oil where most needed.
2) Proper orientation of the rotor in regards to placement of the timer assembly (the word "TOP" found on the rotors was supposed to face upwards in respect to its mounting) would be practiced by the manufacturers to ensure proper oil dispersion after complete assembly.
3) Most units wouldn't be in service for more than a handful of years, that is the owners would buy the latest and greatest to upgrade instead of continuing to use the units.
So is it any wonder that you hear whining and grinding when you plug in a dust-covered 50 year-old clock radio that was used for decades?!
Before focusing on how to rejuvenate that rotor, let's look at the anatomy of a Telechron "H" rotor:
The noise comes from the wear and tear on the reduction gearing sandwiched between the movement plates. The gearing reduces the high speed whirling of the tail shaft's internal rotor (apart of the noise "trouble area") caused by the electromagnetism in the field (the frame that holds the coil and surrounds the "tail" of the rotor). The speed is greatly reduced to a usable 3.6 RPM with enough torque to drive the timer's gearing and of course the hands of the clock. The output pinion (which is clearly visible when you hold a rotor in your hand) is the gear that mates to the actual timer gearing to transfer the motion.
Well, so far we know that the rotors didn't have much of a chance given the fact lubrication was meager, they were ignored for the most part by radio owners and servicers, and for some, used uninterrupted for decades! Now let's give those "thirsty" rotors a second chance!
Here's what you need to perform a non-destructive rotor rejuvenation:
1) Some sort of squeeze-bulb that will be used for storage and application of the oil.
2) A soldering iron of the "heavy duty" variety. A "gun type" with at least 100 watts of power. A simple 40 watt "pencil type" will not do.
3) Some sort of heat-sink. The one pictured below was the audio output transistor heat-sink from a junked 1960s car radio.
4) Last but not least, the oil! Here's the key: you want something that will last a long time and not break-down or turn acidic. It must be compatible with the various materials inside the rotor capsule (such as aluminum, copper, brass, beryllium copper, phenolic resin, stainless steel etc.). It must have the proper viscosity (not to thin or thick) and fairly easy to purchase and work with. Drum roll please...
I use synthetic motor oil! MOBIL 1 "Extreme Formula" 0W-30, to be exact. Synthetic because will virtually last forever inside the rotor regardless of how much use (or disuse) it sees and is compatible with the different rotor materials. 0W (zero weight) as it is the "thinest" and will easy flow inside without impeding the movement of the tiny reduction gears.
Now carefully follow these directions:
STEP 1)
Position the rotor so the output pinion faces up. You'll notice there is a surround that encircles the output pinion. We'll refer to it as the "oil dam" and will be used as such. However, we must first make sure the oil dam and output pinion are completely clean of dirt, debris and old oil residue. I recommend rubbing alcohol and a toothpick. Use the toothpick to pick the junk out of the oil dam and teeth of the output pinion. Give it a quick squirt of rubbing alcohol to wash any remaining residue away. Repeat if necessary and then make sure it is completely dry before proceeding.
Step 2)
Open the container of oil. Carefully squeeze the squeeze-bulb and insert it into the oil. Slowly release while continuing to hold the bulb in place to start the vacuum action--the bulb will start to draw oil from the container. It doesn't have to completely fill the bulb. Close the container of oil and put it in a safe place for use at a later time. A single container of oil will last a long time when rejuvenating rotors! Bring the squeeze-bulb over to where the work will take place. Be sure to have some paper towels ready to clean-up any spills.
Step 3)
Slowly tilt the bulb so the oil trickles out and fills the oil dam up and around the output pinion. Forming a "bubble" of oil that covers the output pinion is ideal. Don't worry if a little bit spills over onto the rest of the rotor around the outside of the oil dam.
Step 4)
Now carefully place the rotor on the soldering iron's heating element assembly. It doesn't have to be at the very tip of the element (to help balance it), but the tip of the iron allows the proper temperature to be reached within the stated time period. Pull the trigger on the iron to start heating up the rotor. Keep it steady and let the rotor heat-up for approximately 40-50 seconds (for a 100 watt iron with the rotor resting on the tip). If you see small air bubbles forming in the oil before 40 seconds, don't worry, this is completely normal.
Step 5)
Regardless if there are bubbles or not, after the approximate 50 seconds have past, it is time to transfer the rotor. Carefully remove the rotor (old salad tongs make a nice removal tool to prevent burning your hand!) and place it on the heat-sink. While it is on the heat-sink, it is recommended you "work the pinion". This consists of using a pin, a toothpick, or a small piece of wire to gently lift the output pinion upward and then push it down again. Do this a couple of times to break any "air lock" that may have formed around the output pinion shaft and the oil dam bushing. We are trying to encourage the oil to flow betwen the small space around the output pinion shaft. Bubbles (air bubbles) are a good sign as it means the heated air inside the rotor is successfully escaping. This means there's a path inward for the oil. Now simply leave the rotor alone while it sits on the heat-sink. The rotor will now slowly "inhale" the oil as it cools due to the vacuum that was created when the rotor was heated-up and then slowly cooled. The heatsink not only provides a safe place for hot rotor to sit, but also aids in speeding up the cooling process.
Do not attempt to speed the process along no matter how tempted. A rapid change in temperature (such as attempting to spray "freeze spray" on it) will only cause fatigue damage from the materials rapidly contracting after being heated.
So how long does it take? Results may vary according to how effectively you heated the rotor, how "willing" the rotor is to accept oil (some are just plain stubborn!), and other outside factors such as barometric pressure. These factors will all play a role in the rate in which the rotor will "inhale" the oil. The rotor depicted took approxiamately an hour to absorb the oil that was placed in the oil dam. To pass the time while waiting for the oil to "magically" disappear, you can focus on the other areas of restoration of your clock-radio. If you inspect the rotor after a few hours and find that none of the oil has been absorbed, you can always try the process again (but try to "work" the output pinion more this time to make sure there are no "air locks" as described above).
You're not done if the rotor successfully took to the first oiling! You must repeat this process for 5 to 7 times. This ensures there is enough accumulation of oil inside the rotor to be of use. After experimentation, I found that more than 7 "oiling sessions" and you are actually adversely affecting the rotor. Too much oil will impede the movement of the reduction gears--resulting in slow or non-functioning clocks and timers. Too little of oil and the excessive wearing of gears will only continue.
If you have successfully repeated the rotor oiling process 5 to 7 times (or as many times before 7 that the rotor seems to accept) you must now follow through with the process of oil dispersion. This will ensure that all internal areas of the rotor are lubricated.
Ensuring proper oil dispersion...
While some may think this is merely the Hokey Pokey for rotors, this guide actually outlines the steps needed to ensure proper dispersion of the new oil (represented in green) inside the rotor capsule. By following the carefully numbered steps, you are saturating the proper areas of the rotor and allowing lubrication to reach passages and shafts. Each position should be maintained using wood blocks or other materials found around the work bench to hold the rotor in place. Leave the rotor in each of the numbered positions for at least 15 minutes to ensure the oil reaches the proper points. Progress through all of the steps sequentially. Steps 2 and 10 show the rotor's output pinion facing downward--don't let the rotor rest on the pinion itself. The rotor must be resting completely flat in these positions.
Step 12--you want to leave the rotor in this position UNTIL you reassemble the Telechron timer unit and reinstall it into the radio. This is because the output pinion area of the rotor "sees" the least oil when installed and in operation in the clock-radio due to the oil draining to the opposite end of the rotor capsule. If the rotor is going sit for an extended period of time before you complete your restoration, it is recommened you alternate the positions shown in step 1 and step 12 every few days.
Other thoughts...
It can be very helpful to test the rotor for short periods of time between steps. I've built a "rotor bench tester" consisting of a field mounted on a stand and wired to standard plug. All I have to do is insert the rotor into the field, and plug-in the field to hear the rotor run.
While your rotor should be quieter than before, it probably won't ever be completely silent. These units always had some noise even when they were new. However, the whining and grinding should stop. If it hasn't, the rotor probably had too many internal problems to begin with. For example, (refer to the anatomy of an "H" rotor picture) sometimes the internal brass surround shifts out of place and collides with the internal rotor. This is unrepairable and is indicated by a tell-tale "scraping" sound when the rotor runs with no load. Don't be disappointed if the oiling procedure didn't work out for you, you have still gained knowledge and experience. Also, think of it this way, the rotor's internals can't get any worse--you've stopped the lubrication problems!
Theoretically, it would be ideal to completely fill the entire rotor capsule with oil to squelch all noise. This is impractical because, 1) it's harder to get oil absorption as the rotor gets fuller. 2) Too full and even the least viscous oils would impede gear movements. 3) As the rotor runs, internal pressure builds up and an over-filled rotor would constantly weep oil out of the output pinion, resulting in a mess.
If you can't find 0 weight synthetic oil, you can use 5 weight oil, but don't use anything heavier.
What do the numbers mean? Each Telechron rotor has letters and numbers printed around the capsule. For example a typical rotor will say "TELECHRON" as well as a scheme such as shown below:
H3 HNK TOP  M2394
3.6 RPM 60-C 4125
"H3" indicates the style of rotor, "H" rotor.
"TOP" indicates this part of the rotor needs to face upwards for proper oil dispersion during operation.
"M2394" (the numbers vary), but this example is Telechron's code that reflects an "H" rotor with a 10 tooth output pinion.
"3.6 RPM" indicates the speed at which the output pinion turns.
"60-C" indicates the rotor is designed for use with a 60 cycle (hertz) alternating current coil.
While some of the information is obvious, others such as internal plant designations and codes are often speculated upon, but still unknown with no definite answers.
The above oiling techniques can also be used on the later "S" rotors (these are the smaller aluminum rotors that were first introduced into the clock-radio industry in 1961).
The later "H" rotors that have aluminum capsules may not be oiled as these "cheaper" rotors used grease inside instead of oil. These can be identified by the aluminum capsule (which does not say "TOP") and a bead of colored expoxy around the seam where the capsule body meets the front where the output pinion protrudes. These were used on the later era clock-radios and served as service replacements for the older brass and copper "H" rotors. Don't confuse these with the smaller, oilable, aluminum "S" rotors which are about half the size of an "H" rotor.
Later rotors may have "GE" or "GE of USA" printed on the capsule rather than "TELECHRON". This is because General Electric owned the Telechron factory and operated it as one of its subsidiaries. Can you guess which clock-radio manufacturer had no problems getting ahold of timers?!
If you use some of your clock-radios as "daily drivers" as I do, you may find it helpful to turn the clock-radio [carefully] up-side-down and at different angles for a few minutes every few months to cause the oil in the rotor to re-saturate the "top" and tail-shaft areas to keep it running quietly. While this is not practical for some radio designs, it will work with most to ensure proper, quiet operation for many more years. "Stay tuned" for more Telechron Timer and clock-radio articles!
Copyright © Dr. Radio 2002 e-mail Dr. Radio
