Reader Questions: Rewiring a 99?

All photos in this entry by Azul from California

Azul from California writes,

I was excited to discover your motor rewiring series, but I have a model 99, which does not have the potted motor and does involve a light switch. The motor is mounted on the side, as seen below.

The Complete “How to Re-wire a Potted Motor”

If you are arriving at this entry for the first time, this is a comprehensive guide on how to re-wire the potted motors found on vintage Singer 15-91 and 201-2 sewing machines. It is my attempt to walk someone with zero experience through the entire process.

For your convenience, here are links to all 20 entries in the series. This way you can bookmark this page as a Table of Contents and quickly get to the entry you need.

Part A: Skills Building

1: Wire, Wire Stripping and Wire Braiding
Learn about the tools and wiring basics you’ll need to know to re-wire a motor.







2: Tools & Materials Required for Soldering
Learn what equipment you'll need to complete basic wire soldering.

3: Learning to Solder
Learn and practice basic wire soldering.

4: How to Terminate Your Wires
Learn how to create connections for attaching wiring to power terminals.

5: Covering Wire Joints with Heat Shrink Tubing
Learn how to clean up exposed wiring.

6: The Underwriter's Knot
Learn how to tie wiring into a strain-relieving knot.

How to Re-wire a Potted Motor, Part 20: Hooking It All Back Up

Now we’re at the final step to getting your machine back up and running!

Start by sliding your newly-renovated motor onto the shaft.

How to Re-wire a Potted Motor, Part 19: Re-installing the Brushes and Grease Wicks

 

With the armature and worm back in place, we’re now ready to install the final items: The brushes and grease wicks, and then we'll re-fill the grease tubes, as seen above. 

We’ll start with the brushes.

How to Re-wire a Potted Motor, Part 18: Re-installing the Armature and Worm

Folks, we’re now very close to the end. Having succesfully completed the actual re-wiring, your machine should now be up and running in no time. But first we have just a few more mechanical steps to get through.

Now we'll start closing the motor up, in preparation for re-attaching it to the rest of the machine. First, grab the worm, and I’ll show you a little time-saving trick.

How to Re-wire a Potted Motor, Part 17: Cleaning the Commutator

Now that our potted motor has been rewired and is partially back together, we need to put the armature back inside. But first we ought to clean the part of the armature called the commutator. The commutator is the series of copper bars arrayed in a ring. They are what the motor brushes make contact with, and they need to be smooth and clean so that electricity can be transmitted between commutator and brush.

The Singer manuals all say to clean your commutator with nothing more than a pencil eraser, but in practice that’s never worked for me. Perhaps it was a valid fix five or ten years into the life of the machines, but some of mine are from the 1930s and require more aggressive cleaning techniques involving a power drill and some sandpaper. The best thing to use is actually a rubber honing stick, but as I'm guessing most of you don't have access to those, I'll show you how to do this with sandpaper you can find in any hardware store.

How to Re-wire a Potted Motor, Part 16: Re-attaching the Field Core

Now we’ll begin closing the motor back up. Please orient your motor as shown in the photo above, which is the way we had it in Part 15.

Then note that there will be a potential problem in closing it up, as seen below:

If we’re not careful, the bottom motor lead will block one of the screws that attaches the field core to the rest of the housing.

How to Re-wire a Potted Motor, Part 15: Soldering On New Motor Leads

Now we’re finally ready to solder new motor leads on. Again, please ensure that your motor is oriented exactly as in the photo below, to ensure my explanations of “top/bottom” are correct:

Motor oriented with field core at left, bobbin winding assembly at top right.

Ready? Let’s begin.

How to Re-wire a Potted Motor, Part 14: Replacing the Motor Housing Grommet

I almost forgot! Before we take the big step of soldering the new motor leads on, there’s one more thing we ought to check, as this is easier to do while we’ve got the motor leads clipped and out of the way. Take a look at the rubber grommet covering the hole that the motor leads will eventually go through.

Here I can see this one has a crack in it:

How to Re-wire a Potted Motor, Part 13: Cutting and Prepping the Motor Leads

Now that we’ve got the motor as open as possible, we’re going to cut the motor leads at specific points to prepare for soldering new ones on.

First, very important, please orient your motor as shown in the photo above: The field core is to the left, the bobbin winder is at the top right. We need to have our motors oriented the same way so when I say “right/left/up/down” you’re not getting confused and cutting the wrong thing.

How to Re-wire a Potted Motor, Part 12: Detaching the Field Core

Now we need to access the motor leads so we can replace them. To get to the motor leads, we need to detach the motor’s core, or field core, from the motor housing. As you’ll see, we cannot detach it completely; although we will physically separate it from the housing, it will remain attached via two wires. (In the photo up above, the two wires in question look like water mocassins.) We must be careful not to disturb those two wires.

The first thing you’ll need to do is remove these two screws.

How to Re-wire a Potted Motor, Part 11: Armature & Worm Removal

With the grease wicks removed (and the motor brushes if they were willing to come out), it is now time for us to crack the motor open. In this entry we will learn to remove the motor cover and perform the crucial task of safely removing the armature. We will also learn the difference between a worm and a worm gear.

How to Re-wire a Potted Motor, Part 10: Motor Brush Removal

In preparation for removing the armature and cracking the motor open, we're now going to remove the two motor brushes. For those of you with no electric motor experience, they’re not “brushes” in the conventional sense; they’re little sticks of carbon that look like charcoal sticks. They reside in a tube leading into the motor and are covered by caps. There is one on the top of the motor, one on the bottom. And as you'll see, inspecting them can provide a good warning as to whether you'll be able to save this machine or not.

How to Re-wire a Potted Motor, Part 9: Grease Wick Removal

Now that we’ve got the motor separated from the machine, we can store the machine someplace else, to free up some desk space. We won't come back to the machine for a while.

Our next goal is to get the motor open. In order to do that we need to remove what’s called the armature, and if you don’t know what that is, you’ll see it shortly. In order to remove the armature we should first remove the grease wicks and the motor brushes, a multi-step process.

How to Re-wire a Potted Motor, Part 8: Motor Housing Removal

Now that we’ve got the motor leads disconnected (as shown in Part 7), we need to remove the motor housing in order to access the motor.

To get to the motor housing, we first need to remove the handwheel. I would ordinarily also disassemble and remove the bobbin winding assembly, but because that is an operation in its own right, I will save that for another entry and leave it attached to the motor housing. (Leaving the bobbin winding assembly on is not “standard operating procedure” for me, but as long as we are careful, we should be fine.)

How to Re-wire a Potted Motor, Part 7: Disconnecting the Motor Leads

Okay folks, time for us to get our hands on the machine.

Before removing the motor from your 201-2 or 15-91, we must first disconnect the motor leads. From here on in we’re going to need lots of different screwdriver bits, so be sure to read the entries on proper screwdriver bits if you’re unclear on this area; if you use the wrong type of driver and strip a screw in the middle of a motor re-wire, you’ll find it a huge hassle.

Step one is unplug the machine. Not at the wall, but at the terminal body.

How to Re-wire a Potted Motor, Part 6: The Underwriter's Knot

This is the last thing we need to learn before moving on to the machine! Congrats if you’ve made it this far.

After we eventually solder new wires onto the motor leads, inside the motor housing we’ll need to tie those new wires into what’s called an underwriter’s knot before we push the wires out through the housing.

An underwriter’s knot provides strain relief, so that if we tug and pull on the wiring while we’re installing the motor, it will not place any stress on the motor leads where they join with the motor’s field core. (The knot will simply catch on the inside of the housing.) This is very important, because if you break that connection at the field core, your potted motor then becomes a potted paperweight.

We’ll practice outside of the machine to be sure we can get the knot right. Ready?

How to Re-wire a Potted Motor, Part 5: Covering Wire Joints with Heat Shrink Tubing

Now that we’re able to solder two wires together, we’ll use heat shrink tubing to cover the soldered joints. It’s quick and easy.

Heat shrink tubing is just a little tube of thin, rubber-like material. You cut it to length with scissors. Then you slide it over your wire joint, apply heat with a cigarette lighter or heat gun and it shrinks a predetermined amount, acting as insulation and protection. It comes in different sizes and many different materials, but there's a particular kind we need.

How to Re-wire a Potted Motor, Part 4: How to Terminate Your Wires

If you are able to solder as shown in Part 3, congratulations! That’s the most difficult part to learn. These next few things are much simpler in comparison.

Once we finally replace our old motor leads with new wiring, we’ll need to connect the ends of that new wiring to the “3-Pin Terminal Body,” which is this thing:

When we detach it later, you’ll see that inside are three threaded brass studs:

The wires need to connect to these studs. We’ll eventually connect them by either a) crimping pre-bought ring terminals onto them, or b) creating ring connections on the ends of the wires ourselves. I’m going to show you both methods so you can decide which you prefer.

How to Re-wire a Potted Motor, Part 3: Learning to Solder

Once you’ve mastered wire stripping and braiding (as shown in Part 1) and understand the tools you’ll need (explained in Part 2), we can get down to actual soldering practice.

First thing I’ll say is, a soldering iron is dangerous. So is a kitchen stove and a steak knife. Because we learn early on to use a stove and a knife with care, we can use them daily without having any accidents. That same care should be taken with a soldering iron. Here are some steps I recommend:

A. Clean up your workspace. The soldering iron needs a dedicated place to rest where nothing else is near it. The tip gets extremely hot and there should be no chance it will accidentally touch anything, either while it is at rest or while you are using it. Remove all obstructions from your work area, leaving only the things you will need to do the job.