Saturday, March 16, 2013

Singer 401A Cam Stack

The Singer 401A is considered by many, including the Singer Company at the time, as "the finest zigzag sewing machine made". The company had good reason to be proud of their 401 though. It was built with precision and had scads of built-in stitches, plus it had the option of using Singer top hat cams. To top things off, it was 100% gear drive.

I recently acquired a second 401A machine and decided to prep it for sale. After popping the top cover off, I noticed the cam stack was quite discolored with old oil remnants and decided to venture into the unknown realm of cam stack removal. It was actually quite easy. The top screw that holds the top hat spring clip is all that holds the cam stack in place, so once that screw is removed, it is just a matter of getting the cam follower fingers out of the way and the stack lifts free of the machine.

Three small screws on top of the stack hold all the pieces together, but after 50 years of being clamped together, it took some gentle persuasion to get all the cams apart.

The cams are numbered 1-7 except for number 5, which had no markings whatsoever on it. The cams have three holes each (small, medium and big) around the large center hole, so it is pretty much impossible to get the stack back together the wrong way, as long as cam 7 is on top and all holes line up according to size.

Here is how I started reassembly.

I lightly oiled everything also so the cams wouldn't rust. The next photo shows the cam stack back together in one piece.

Next thing to do is to pop the cam stack back in place and re-time the stack to the needle. There is a timing mark on cam 7 that you can see below. It is lined up with one of the cam followers. This timing mark needs to be lined up with the follower when the needle is at its lowest point of travel. Then just tighten the three small screws on top of the stack and everything should be set to go. No, I didn't bugger up the small screw heads. A previous owner or technician did that.

As many owners of 401s (and 500s) know, the two posts that the cam followers slide on are notorious for getting gummed up and refusing to work properly. It is just a matter of getting them cleaned up and oiled, at which time the stitch selector mechanisms should work again. The two posts can be seen in the next photo, one on each side of the cam stack post, and having the notches in the sides. You can also see the grime in various places that hadn't been cleaned up yet.

The 401A is really quite the mechanical marvel. It is fairly easy to work on but at the same time is very complex in its combination of stitch patterns. I highly recommend either the 401 or the 500, or both. You can never have too many sewing machines. That's my motto and I'm sticking to it.

Update 1/23/2016:
"Practice" asked the question about a spring they found in their machine. I took the cover off my 401 and took a couple photos showing where the spring attaches.

In the first photo below, the spring is in the upper right. It attaches to a small "hook" about 3/4-inch to the right of the red dot in the center of the photo, and just to the right of the brass-colored screw.

In this next photo, the other end of the spring can be seen attached to a rod. The spring can be seen about a third of the way down from the top of the photo.


  1. I just came across this post today and I am so appreciative that you've taken the time to post the most helpful information on the cam stacks that I've found thus far. My one question would be what did you use to clean them with. Thanks so much!

    1. I used mineral spirits (paint thinner) to clean the parts. Something stronger would have worked faster but I used what I had on the shelf. The parts are steel and brass so I imagine just about any cleaner would work. Thanks for the comment.

  2. I have been trying to refurbish my 401A. I haven't been able to get the cam stack to come apart. Is that necessary for the machine to run smoothly? Also when I have tried to reinstall the cam stack, the machine drags very much and I would be afraid to try to get it to run, while when the cam stack is not installed, it purrs like a kitten and runs so smooth. What is the trick to getting the cam stack reinstalled? It is very difficult to push down and then the followers don't work very well and they drag very hard, while otherwise without the cam stack installed they function smoothly. Thank you for your help.

    1. That adjustment is a bit tricky..First loosen the set screw that holds the "pinion" the cam stack sits on.. There is the possibility a previous "repair-man" got his hands on it and "mucked it up"- I have had to learn to "un-do" the butcherings of several repair-men.
      This is accessed after you first remove the light cover. Underneath you will see a large screw head. With either an off-set screwdriver
      or a small stubby slot driver, slightly turn the screw until the cam-stack easily slips on ( with out any motor binding). When the cam-stack is properly seated, the black clip which holds the removable cams should turn freely- but the cam-stack should have little "up or down play". If the black clip is not freely moving, this is an indication the pinion is pushed down too far and need a tiny coaxing up.
      In these older machines it may be a good idea to spray a little WD-40 before attempting an adjustment. And use the proper size screwdrivers..nothing is more unsettling than to open a machine and see all the screw heads mangled. Remember these are all very minute adjustments, only a slight amount of movement is needed, and do not make the final "tighten" until you are certain the machine is running "fast and smooth".. You may need to try a few times to get it correct. Do not attempt this if you are tired or if you feel frustrated, step away and return when your nerves have settled..These are tricky adjustments.. My "pet peeve" is when the zig zag is not centered. Out of necessity, I ordered the professional repair handbook and studied it. I do all my own adjustments.. I ordered the repair manual on E-bay and could not be happier knowing I can put a Slant-O-Matic back to its "showroom condition".. I wish you the best of luck.
      Regards, Richard Ransom Beman

  3. Thank you for showing how to remove the cams for some reason my multi stitch zig zag doesn't work (BQ) I removed cleaned and oiled the cam stack but my gears are still frozen how can I disassemble clean and oil those?

  4. My 403 has the same top hat cam gears but one of the three prongs of the clip spring has broken off. It's still working with two prongs but I am afraid a second one may break and I will not be able to use the cams at all. I have searched the Internet high and low and couldn't find a replacement spring (only seen it on eBay once). Do you know where I can find a replacement clip spring for it? Thanks

    1. No, sorry. I'd just recommend you keep looking online. Maybe one will pop up. Good luck.

    2. It is the same clip used on the 600 series Touch and Sew machines..The 400-500-600 all used the same clip.. That should make it easier to find. It's possibly worth it to find a 620-648 machine with stripped plastic gears to use for spare parts... That is how I have "stock piled" many extra goodies ( space is an issue, I have them in plastic boxes). Parts are impossible to "simply order", so when
      one loves these older machines it is necessary to "hoard" spare parts..Its either that or buy a non- repairable computerized machine.
      Lot's of luck, Richard Ransom Beman

    3. I don't know if you will see this post but it pays to have more than one machine. your best machine can be used for sewing and another one or two for parts. You can often find an old machine that is less expensive than the part you are searching for.

  5. I enjoyed reading your post and am hoping to find an answer to my latest stumper. I recently acquired a Singer 401A and have been cleaning it. I was able to unstick the stitch selectors (good old hair dryer and smo). While I had the top off, I found a spring laying on top. I'm guessing its for the needle position control. I can freely move the control and the parts inside move but the needle and the bar above it don't move. I can also move the needle side to side, but it doesn't move the top pieces or control. So, I'm assuming that spring is needed. But... Where the heck does it attach? I've looked at the users manual and the service manual and can not see it in the diagrams (doesn't mean its not there, lol).

    Anyone have any experience with this spring? Am I on the right track? Help... Please.

  6. i am having trouble getting the spring back into the black disk on the cam stock what am I doing wrong Thnak you for your help Roberta robzik60@