I bought my machine used, and it was running fine when I got it. At least it sounded fine, I haven't seen it sew nicely yet.
I followed instruction to lubricate it, using Tri-Flow oil (and grease where appropriate) and it seems to run great. It was apparently almost never used (or was very well maintained).
Mine is serial number NB829xxx, manufactured in 1960 at the Anderson, South Carolina factory.
The bobbins are Singer part 172222, also referred to as "class 66". These are easy (for me anyway) to recognize, because they only have a few holes. I have two kinds. One kind just has a single small hole. The other kind has 3 big holes and one little hole. The bobbins for my other Singer machines have lots of holes, all the same, equally spaced all around the bobbin.
As a side-note to myself, the 401a bobbins are not the same as used in the Singer 237. The 237 uses "class 15" bobbins (part 2518-A). They aren't the same as the bobbins for my Featherweight 221 either. The 221 uses part number 45785.
Remove the needle plate, bobbin, and bobbin carrier. Operate the machine by hand and watch the "hook" go round and round. The main point of this is to identify the hook itself. Now, put a needle in the machine, thread it and operate the machine by hand. As you pull the top of the hand wheel towards you, you should observe the hook moving counterclockwise The needle should go down, then the hook moves from right to left and catches the thread as it passes the needle. If the hook passes the needle after the eye of the needle has lifted above it, the machine timing has slipped and repair is needed. My machine was fine when I performed this check.
Most of the following are videos. These vary in quality and I have omitted some where the people talk in a way impossible to understand or the video jumps around in a way to drive you crazy. Even some of the videos I do include are marginal but are retained because they do provide useful information. As the saying goes, you have to learn to eat the fish and spit out the bones.
Christopher Nejman deserves special recognition for producing some truly nice videos.I like the videos by "Archaic Arcane", but sometimes she talks really fast and is impossible to understand. It is worth the effort (and possible replaying as needed) because she presents valuable information. In particular, I learned a lot about the tension mechanism from her. For some reason, both of here videos of the tension mechanism start with the mechanism already taken apart and removed from the machine, which is bizarre. I throw the video by the Gballz factory in here. It is short with no sound. You should watch it first once, then carefully watch "Archaic Arcane"'s videos.
Lourdes Johnson has done a bunch of nice videos on the 401A. For the most part, there is no sound, which has certain advantages.
I like the way "Sourdough Girl" talks slowly and clearly.
The following video was helpful for finding my way around my machine for the first time, but is misleading in several areas.
This guy (?!) takes the general approach of blasting everything with Tri-Flo. Now Tri-Flow is great stuff and this might be a possible approach for a frozen up machine, but a more restrained approach would be correct for a machine in good working order. If you do what he says, you will have tri-flow dripping out of the machine for days, soaking your thread when you set up the machine, and so forth.
I am skeptical about the need to put grease on the cam stack. I am even more skeptical about the claim that excess tri-flow will not collect lint.
His lazy approach to cleaning the tension mechanism is plain wrong. I disassembled mine, cleaned the disks with acetone, and followed Archaic Arcanes video to get it back together easily and in calibration. You don't want Tri-Flow on the tension disks. Apart from the fact that things won't work right, your thread will be forever flossing tri-flow out of the tension mechanism and making a big mess out of whatever you are sewing.
Tom's home page / tom@mmto.org