First a picture for those wondering what a Singer “potted” motor is…
A potted motor a direct gear drive motor where the motor housing is attached to the back of a so equipped Singer sewing machine. The motor drives the sewing mechanism via a gear on the balance wheel. The motor case protrudes from the back of the machine and kinda looks like a pot… a potted motor.
Singer only offered the potted motor on a few of its machines, these include the Model 101 (different design), model 15-91, and the model 201-2. Some have described the Singer potted motor as the best sewing machine motor ever made for a sewing machine. I don’t know about that, but I do agree it is a fine motor. They are still found on many machines running today that were manufactured when it was first introduced in the 1920’s . Imagine a sewing machine motor made today that will last 100 years.
In my opinion, it has some drawbacks. First of all, if it does go bad, it must be replaced with another aged vintage motor. They are not manufactured today…. even in China. The machine will not work with any other style motor. An external motor on the other hand can be replaced easily. This is a serious consideration for someone considering a Singer model 15-91 (potted motor) or a Singer model 15-90 (external motor and belt). The machine doesn’t care what runs the sewing mechanism… I would bet that there is someone, somewhere, who adapted their belt driven sewing machine to power it with a chainsaw motor… I’ve thought about it myself. Anyway, that’s off topic. This tutorial is about restoring the potted motor on your machine so you don’t need to replace it.
As I said, it is a great motor and it was designed to be serviced and repaired. The achilles heel for these motors, and most likely why you have read this far, is the wires. They all suffer the same fate. The motor was designed to last for decades, but unfortunately, the wires don’t.
So, getting on with this tutorial, I must tell you up front that it is a long and extensive blog because I am going to show you how to restore this motor to the highest degree possible… There are instances where a motor will burn thru a winding (The thin copper wires wound in the motor), in which case, there is no hope left and a replacement is the only cure. I can’t wind a motor, you can’t wind a motor, and if you did find someone who could wind this motor, the cost would not justify the service. Still, there is much that can be done to turn the clock back decades to restore this motor to its youthful vigor, and this is what I want to share with you in this tutorial.
The steps will be shown in order of process. To try and keep this post to a reasonable length, I will not use much space for discussion, but will caption the pictures to describe the steps. If I think I need to explain something outside of captions for clarity, I will stop and do so. You can do as much or as little as you want. No matter how deep you go, the reassembly from a certain point is simply the reverse steps up to that point.
Note, the pictures in this tutorial show several different potted motors, It ain’t a “bait and switch”, but because I document all of my restorations and I have plenty of pictures combined to show each step in detail. The grease that I refer to for the grease wicks is petroleum jelly. Don’t frown just yet, the reason is revealed in the tutorial. The grease for the worm gear is Tri-Flow synthetic grease, Singer sewing machine grease will work well too… but use these only on the gear, not for the grease wicks… yep, two different grease types for two different applications. That said, lets begin:
Remove the balance wheel by loosening the stop screw in the stop motion knob on the back of the balance wheel. Set aside the balance wheel, the stop motion knob and the washer for reassembly. Removing the bobbin winder aides in cleaning. This means removal is optional. It has springs that for some folks can be difficult to reassemble. Don’t disassemble if you are unsure… better safe than sorry.
These 2 screws are tight. They must be removed with a tight fitting screwdriver. The easiest way to remove these is to press the screwdriver hard into the screw slot while lightly tapping on the end of the screwdriver with a hammer as you are trying to loosen it. This impact will loosen them, simply trying to loosen them with all your might will not. This is most important… You will NOT get them off simply trying to loosen them. What you will do is strip out the slots trying. Use a little impact, it works. Lay the motor on your bench.
Important! There is a thin washer on the armature shaft. You may not notice it immediately, but it is there. Be careful that this washer in not damaged or lost. It prevents the motor grease from migrating into the motor housing. You can see it here.
Moving on, the next steps require soldering and desoldering. To be successful, you need a hot soldering iron. I use a digital soldering station at a temperature of 450 degrees centigrade, or a hand held 250W soldering gun. A small hobby or wood burning soldering iron may not get hot enough to handle this size wire. The most important consideration in any de-soldering/soldering operation is that you need enough heat to melt the solder quickly. To much time melting the solder will heat the wire and possibly damage the insulation. Note: This step is not necessary but for my needs it is part of a potted motor restoration. Likewise, the motor housing can be cleaned without removing the brush tubes.
Next we remove the grease wicks.
Lay all of the parts out for cleaning and keep track of them… there is a lot of grease and small parts sticking to this grease are lost easily.
With the motor housing stripped, it, the spiral gear, and the grease wick retainers are soaked in kerosene for about 24 hours to dissolve the grease. Kerosene will dissolve the grease without damaging the paint. All other parts except the motor brushes, field coil, and armature are ultrasonically cleaned. They can be cleaned manually.
Next the main wires are replaced… I use solder connectors for ease and a good solid joint. I find it difficult to “twist” the new wires to the old wires… remember the old wires are brittle. I make my own as follows.
Next, the motor can be reassembled. Remove the old grommet. Make sure the new wires are routed through the grommet hole and gently pull on them as you are seating the field coil. The key is to make sure the wires are not going to interfere with the armature and have clearance in the housing. The commutator and armature shaft is polished before reassembly. I use jewelers rouge on the commutator and 2500 grit wet/dry sandpaper wetted with oil on the shaft. In lieu of jewelers rouge, the commutator can be polished with dry 2500 (or finer) grit sandpaper. For polishing, chuck the shaft in an electric drill and spin it at a moderate speed. Wipe with a clean cotton cloth to remove traces of oil.
Reinstall the springs and brushes in the brush tubes and gently tighten the bakelite brush caps. They do not need to be tight… snug is good. To much tight and they can break.
Install a new rubber grommet on the motor housing where the wires enter. It is a 3/8″ rubber grommet available at most hardware stores.
Almost there… the hard part is done. Only the grease wicks and end connectors remaining. If you opt not to replace the grease wicks, the old wicks can be cleaned with dish detergent and plenty of water. The cleaned wicks (thoroughly rinsed) can be dried in the oven or toaster oven at a low temp… 170 degrees for an hour or two is sufficient. Keep in mind, cleaning the wick is acceptable only if the wick looks usable, that is, it is still pliable and not hard from the old grease. Also, the wick should not be stretched or rolled thinner. It needs to fit properly in the motor housing.
Reinstall the grease wick caps and the armature end cap. Wondering about what motor grease to use? Use 100% unadulterated petroleum jelly… the cheap stuff with no additives. There has been much debate on this… but it has the proper melting point for these motors and provides adequate lubrication. If you are unsure or don’t believe me, research the topic online. I’m not being cheap here, a substitute is necessary. The simple fact is that these grease wick motors have not been produced for a very long time, and the stuff originally formulated for them is not available anymore.
Now trim the new wires for final length. Reinstall the motor on the machine and route the new wires to the wire plug connector. Leaving about an inch or even a little longer is better than too short. The end connectors from the old wires are reused.
Coat the worm gear and the textolite gear with a good quality grease. I use Tri-Flow synthetic grease for this purpose. Now would be a good time to restore the shock absorbing mechanism behind the textolite gear. It is not hard and you are halfway there with the balance wheel off. Its easy and takes about 15 minutes. See my blog showing how this is done at:
If you choose not to do this now, you are done!
Now the motor has been restored, it is important to “run it in”. This simply means run the motor on the machine with the sewing mechanism disengaged… Run the motor at full speed. You may notice that it runs slower and then faster. This is okay. Keep running the motor until it picks up speed. You will hear the speed increase. Run the motor until the end cap starts to feel warm to the touch. Alternate the speed from fast to slow. The purpose here is to seat the brushes and wicks. As the motor warms, the petroleum jelly will melt, fee the wicks, and lubricate the shafts. The motor will break-in after some use and you may notice some increase in speed. All of this is normal, and the motor should be good for another few decades!
That’s it! Your patience and attention to detail will pay off if you choose to restore your motor, I hope that this tutorial has helped you and answered a few questions in the process. Don’t hesitate to contact me if you have any questions, and please visit our Etsy store at https://www.etsy.com/shop/pungoliving, to see our restored fine high quality sewing machines.
As always, our tutorials are provided as a free resource to help you learn and maintain your vintage sewing machine. As our site has grown, so has the cost to keep and maintain it. Despite these costs, I will strive to continue posting tutorials and other relevant content for the benefit of the sewing community. If you found the content of this tutorial useful, please consider making a small donation to help me grow the site and help defray my costs… every little bit helps.
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