Tuesday, December 20, 2011
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.
I start by using a large rubber band to get the motor leads out of the way. (Please note this demo was shot twice with two potted motors. Please excuse any cosmetic differences between the two.)
Removing the grease cup caps
We start with the grease cups, two short shafts that contain the grease wicks and some other fun stuff. The user is supposed to periodically fill the grease cups with grease, which the wicks then deliver to the armature shaft to keep it nice and lubricated so the motor can turn freely.
The grease cups are enclosed by two large, knurled caps:
Sometimes you can unscrew them by hand, but other times they’re stuck fast by old grease. If you cannot unscrew them with your fingers, it’s time to move to Plan B: A penny and a pair of pliers.
In the process of doing this you may ruin the penny, but that will still make it the cheapest tool you ever bought.
First stick the penny in the pliers. Then use the pliers to stick the penny into the slot of one of the grease cup caps.
But don’t start unscrewing yet; while the penny is in the slot, slide the pliers further onto the penny so that there’s no space between the pliers and the grease cup cap. This will give you better leverage. Then you can easily unscrew each cap without totally twisting the penny out of shape.
After removing both caps, if the insides of the caps themselves are covered in old, hard grease, I wipe off what I can, then drop them in a shot glass with some rubbing alcohol, to loosen the old grease up. They caps will soon be joined in the glass by some friends.
Removing the grease wicks, springs, and retaining clips
Turning back to the grease cups, with the caps removed, we see this:
What we’re looking for is a little rectangular tab that lets us know where to place our tweezers or forceps. In the photo above, you can see the rectangular tab in the right grease cup but not the left.
Look at the same photo with some red dots that I’ve added. Those dots mark where you would insert a pair of tweezers or forceps. Read on for an explanation.
The left grease cup is completely filled with grease...
...but if we scrape some grease out we eventually see this:
What we’re looking at is the top of a little metal retaining clip that holds the grease wicks, and a spring containing them, in place. To remove this retaining clip, we need to stick the points of a pair of tweezers/forceps where the red dots are in the photo below.
Stick the points down into the cup just 1/8 to 1/4 of an inch past the tab, or a few millimeters for those of you living in countries with a more sensible measuring system.
Then squeeze the tweezers very gently and pull straight out of the grease cup. The retaining clip should come out with the tweezers. If they don’t and they feel like they’re stuck, squeeze just a little bit tighter--be gentle so as not to overly bend the delicate clip--and try again.
Sometimes the retainers come out and bring the spring & wick with it, other times it does not.
If it does not, look in the hole and you'll see the spring.
Pull it out, gently, with the tweezers. They should come out with the wick. If for some reason they don’t, fish around in the hole with the tweezers and pull the wick out. (This may be a messy process.) After you’ve done one grease cup, don’t forget to do the other.
Once the grease cups are empty of all this stuff, I generally scrape out whatever old grease I can get out of the cup. But I do not use any solvent or liquid here, as we don’t want any of that stuff riding down the armature shaft and into the motor. If you’re really intent on cleaning the grease cups out completely, do it later, after we’ve gotten the motor apart.
Also, as you’re scraping, please note that the inside of the grease cups is not a perfect cylinder, so if you hit a hard obstruction with your scraper, don’t go nuts trying to dislodge it; there is a “step” inside.
The next thing I do is get the old grease off of the retaining clips, either with a scraping tool or Q-tips. Then I “unscrew” the wicks from the springs. (This is a messy process and was impossible for me to shoot with both hands engaged and covered in grease.) While trying to free the wick from the spring, you’ll occasionally find that the end of the spring has been purposely bent and stabbed into the wick to hold it in place, which can make it a pain to remove; please do this cautiously, as we do not want to stretch the spring out and deform it too much. That creates more work for us later.
Here you can see that, despite my best efforts, I’ve slightly deformed the second spring. I’ll have to correct that later when we get this all back together.
After removing what grease I can from the bare springs and retaining clips, I throw them into the rubbing alcohol. After they’ve soaked enough to break the grease down, I clean them off with Q-tips.
A word about grease wicks
I always replace the wicks since they are frequently old, hard, filled with crusty grease and can no longer perform their wicking action. I have heard of people washing the wicks out but have never done it myself.
I order my replacement wicks from McMaster-Carr. Due to the layout of their website I cannot provide a direct link, but to order some you need to click here and enter part # 8767K226 in the search box. Unfortunately they only sell it in five-foot lengths, for $5.35, and we only need a couple of inches; but I have not been able to find another place that sells felt wicking. If you know of one, please
mention it in the comments.
We will replace the wicks later, after all of our soldering is done.
Go on to Part 10: Removing the Motor Brushes