Wednesday, January 25, 2012

Reader Questions: Eric's Knee-Operated 15-91

All photos in this entry by Eric from Ottawa

Eric from Ottawa writes,

[The 15-91 I recently acquired] looks like it's in great shape, but it doesn't run. It has a knee switch rather than a foot pedal and it looks like the motor controller has failed. 

To test it, I unscrewed the center of the flywheel so there was no load and plugged it in and got nowhere, even with the knee switch in and fully engaged.

Do you think it's worth re-wiring it to use a standard foot pedal like most of the ones I've seen?

Hi Eric, first off, a little about your machine. The chrome rim on the handwheel plus the design on the faceplate, from the little bit of it that we can see in the photo up top, indicate this machine is from the 1930s or early 1940s (assuming those parts are original). The old-school cylindrical Singerlight visible in the photo below also indicates the machine is from that era.

The “J-“ prefix on the serial number plate indicates your machine was made in Singer’s Canadian plant in Quebec.

Secondly, good on you for trying to run the motor with no load, that’s exactly the correct first step to test out a motor.

As you’ve observed, your machine uses a knee-activated controller.

For those readers unfamiliar with this device, it was an early alternative to the foot pedal most of us know, and it eventually fell out of favor. It consisted of a motor controller placed in the right side of the wooden base:

The end of the removeable knee lever--which stows handily inside the case and underneath the machine, or occasionally up in the domed lid via clasps, when not in use--“plugs” into the hole in the front of the case.

Pressing against the lever would activate the motor controller, which is wired into the inside of the three-pin terminal.

Eric, there are three possibilities here: 1) The power cable is faulty. 2) The motor controller is faulty. 3) The potted motor itself is faulty. Hopefully it is #1 or #2 and not #3, as the first two are easy, relatively inexpensive fixes.

To see if it’s the power cable, try turning the light on. That’s not a 100% accurate test because the bulb may be burnt out, but at the very least, if the light does turn on you know there’s power flowing through the cable. Another thing you can do is bring your cable to the house of a friend with a vintage Singer--that cable will fit a variety of machines made in the 1930s, ‘40s, ‘50s and some in the ‘60s--and see if it powers his/her machine okay. If you determine your cable is what’s faulty, you can order a replacement from Sew-Classic for US $7.95 right here. If you choose to go with a different supplier, perhaps someone local to you in Canada, note that you’re looking for a “single-lead” (as opposed to “double-lead”) cable.

If the motor controller is the problem, it is totally “worth re-wiring it to use a standard foot pedal,” to answer that question, and the good news is that it doesn’t quite require “re-wiring.” The motor controller leads are easily removed via two thumbscrews inside the three-pin terminal. There’s no cutting of wire or soldering required, it’s a simple mechanical connection. To see how to remove the leads, click here and look at the parts of the entry that pertain to removing the two motor leads, which in your case are really the controller leads. Be sure to note which two pins in the terminal those leads connect to.

To replace your motor controller with a foot pedal, you’ll need to spend a tad more. You’ll need to buy a foot controller; the least expensive offered by my preferred supplier, Sew-Classic again, goes for US $11.95.

What you can do is connect the two leads from your new foot pedal to the same two posts that you disconnected the original motor controller leads from. Then you can remove the old motor controller (attached via screws) from that compartment on the right of the wooden base, and store the pedal there.

Alternatively, if you’d like an original Singer foot pedal, you can check eBay.

If it’s the motor that’s bad, then you’ve got a fair amount of work ahead of you to figure out what exactly is wrong with it, and if it’s fixable. You may want to browse the complete “How to Re-Wire a Potted Motor” to determine how to disassemble the motor so that you can inspect the wiring, one possible culprit. But if it’s something beyond bad wiring--a burnt-out field core, for example--that’s beyond the range of my fix-it knowledge.

If you do determine the potted motor is what’s faulty, you will occasionally spot someone selling one on eBay.

Whatever you do, please don’t throw that motor controller out, even if you determine it’s bad; if you stay in this hobby long enough, you will eventually encounter someone else who may need a part from that controller--even if it’s just a single screw--so you may be able to help them rescue an otherwise non-functioning machine. Ditto with the knee lever.

Best of luck with it, congrats on the machine--I love those chrome-rimmed handwheels!--and let us all know how it turns out.


  1. A quick follow up.

    Good news followed by bad.

    With the existing two wire plug the light works I have a functioning cord and light.

    I was able to get the pedal controller from an old 128 to test with and set forth to open up the plug.

    The motor was wired across 3&3 and the knee-controller wired across 1&2.

    I tweaked it so the motor was on 2&3 to match the foot controller (and the wiring diagram on the sew-classic site -

    Still nothing.... Sounds like it's the motor which makes me a little sad. I'll read through your tutorial on the motor to see if there's something obvious like a broken wire and then I guess I'll attempt a replacement on the motor.

    It's too bad since the motor wires are in almost perfect condition.

    Thanks again for your feedback.

    1. Eric, with any luck it will be something simple like the brushes not making proper contact. Go through the Potted Motor tutorials to find the part on removing the brushes, and check those first. "Always start with the easy stuff."

      - Rain

  2. Yup.. I fully disassembled the motor and found a couple issues:
    - There was a thin grease in one of the brush ports and it didn't look like it was making good contact.
    - There's evidence of a soldered repair of one of the winding wires.

    The interior was pretty clean but has some signs of corrosion. I worry that the core doesn't turn as smoothly as it should. I cleaned everything up but don't have replacements for the wicks or grommet.

    I checked and there's continuity on both wire coils and I cleaned up the commutators.

    I put it all back together to the motor testing in stage #20 and it tries to run but jams. There must be too much drag on the motor to start properly.

    on one of the coils in the motor the paper cladding has come off, probably from the soldering which replaced the wire right back to the fine wire.

    Do you think it's worth stripping it and doing a more thorough clean and replace those wires?

    1. Not sure if you're aware, but there should not be *any* grease in the brush tubes, and if there is, you certainly need to remove it all.

      If the motor runs but jams, that's at least a positive sign in that it is trying to turn over, so there's some life there. Impossible to diagnose from afar but I suspect there's an issue with both brushes not making good contact. But now it will be up to you to determine where the jam is, as that's a very hands-on diagnosis and fix. With the armature in place and the potted motor cover off, are you able to turn it smoothly by hand? It should spin freely enough that if you give it a good spin and let go, when you let go it should almost feel like it's going to keep spinning for a bit (though it won't actually do that).

      To answer your question I definitely think it's worth a shot, as these motors are not that easy to come by; the question is whether *you* think it's worth it, as the results are not guaranteed.

      If you need more detailed guidance--that paper cladding being gone is a source of concern--now may be the time to sign up for the "WeFixIt" forum on Yahoo Groups, which is populated by experienced mechs with way more experience than me.

      hope that helps,

      - Rain

  3. Eric, what a great machine, hope you get it going.

  4. Rain- I find myself wondering how you are, no post in such a while...your past tutorials have been so helpful!

  5. I just bought a '55 Singer 15-91, Knee Lever Operated, in semi working order - The potted motor was and is strong, and in great working order, tested by removing the load on the motor (IE: clicking it over to bobbin winding).

    I found that the entire rest of the machine's moving parts needed a generous helping of oil, and lots of time to sit, and soak it up - Overnight. I used about 1/2 a bottle to basically hose off the machine. Totally got oil everywhere but she ran like a top the next morning, and there was no excess oil to wipe up.

    The thread tensioner gave me fits until this morning - late last night it dawned on me to try the simple fixes before I disassembled it. Again, I brought out my trusty Singer Sewing Machine oil, and "hosed off" the thread tensioner. This morning I was able to run a stitch perfectly - and the upper thread, that had been snapping about 1/4 of the time going forward and 100% of the time going in reverse, worked perfectly.

    My question now is, where can I go to learn what all the extra feet are for, and how to operate this machine properly? I can't even find museums that have antique sewing machines from that time period to go look at, hoping to find a volunteer there that can tell me more.

    I plan on calling/going back to the antique consignment shop that I bought it from (for $80 including everything and the cabinet) and asking if the owner knows more. I'd love to work up a historical binder on this machine.

    How do I go about contacting Singer for a Certificate of Authenticity also? That would be a really neat addition to this machine's binder.


    1. Lisa, it's been months since you asked, but just in case you haven't found it yet, the manual for the 15-91 is here:

  6. I have the Singer 206D from Germany serial Number starts with a C and the decal on the front says Wittenberge Germany. the motor works but it doesn't sew ?? something is wrong with the bobbin case and the only ones I can find are for the 206K ??? It's a different machine and also I read that this machine does not take the 206X13 needles instead it takes the 15X1. I also wanted to know if Kai Albers (who has the same machine and has written to you) can tell me where to find the Manual for the 206D I have the manual for the 206K but again it is a different machine. I brought it to a repair man and he said it goes but will not sew because of the bobbin case.

  7. What a great blog I found! Thank you very much for all the info here.

    I saw a 15-91 on sale. I believe the seller replaced the motor with 1.5amp. Will it make any difference to its ability to sew heavy duty canvas or many layers of jean materials?

    One more question: Choosing between original well-kept 15-91 or beautifully refurbished (cosmetic-wise, wiring and replaced peddle) which one is a better choice. Thanks very much in advance


  8. "the seller replaced the motor with 1.5amp. Will it make any difference to its ability to sew heavy duty canvas or many layers of jean materials?"

    I doubt that's a 15-91 then, as you cannot easily attach a replacement motor to a 15-91; the potted motor is a proprietary design.

    To answer your question, I'd say probably not. The 15-91 is already powerful enough to punch through a few layers of canvas and hem a pair of jeans. What exactly is it you're trying to make? Please be specific so I can recommend an appropriate machine.

    "Choosing between original well-kept 15-91 or beautifully refurbished (cosmetic-wise, wiring and replaced peddle) which one is a better choice."

    I don't know, which one works better? What is different about each machine? Without that information, I don't have enough data to answer your question.

  9. I recently picked up a 15-90 that someone was giving away. It has a foot pedal that stores up inside the machine as well as the knee lever. Is that unusual? I think it's a great machine. It's my first Singer and I'm in the process of cleaning it up.