Documented Fix: Singer 237 Tension Assembly

I only collect and repair certain models of black cast-iron Singers made through the 1950s, and those are all I planned to cover in this blog; but when my neighbor mentioned she had a thrift-store 237 that was giving her problems, I couldn't help but take a look. (While I solved the problem, this post will be more of a documented fix than a tutorial, as I've only performed this procedure a couple times and don't know it thoroughly enough to try to teach it yet.)

First thing that jumped out at me was the duct-tape spool pin. I don't know much about the 237 except that it's from the '60s, and my first thought was "Wow, Singer really started cutting corners." My neighbor confessed to creating the spool pin.

I started reading up on the 237 on the Yahoo Vintage Singers group--it is a wealth of information--and found that it's actually a well-regarded zig-zag machine, the last of the all-metal interiors Singer made (although the little door that holds the rotating hook in place is plastic).

She said the machine was giving her tension problems. When I first encounter a machine, I never plug it in and start running it, not since I found a finish nail buried inside a 221, and a 201 with a mis-installed hook retaining ring. Had I plugged either of those machines in and hit the gas, I might've wrecked something. So I always eyeball the machine first.

Giving the 237 a visual once-over both inside and out, it finally hit me. Folks, you notice anything unusual about this photo?

Let me zoom in for you:

Yep, while I don't know this machine at all, I'm pretty sure the tension assembly is not supposed to be shaped like the end of a ski jump. I'm guessing this machine was dropped. However it happened, there's no way you can get consistent tension if the two tension discs can't cleanly come together, and they can't if the stud they're riding on is bent like that.

I've had to fix this on one of my 201s, so I sort of knew what to do. First step is to disassemble the tension assembly. In this case, the split ends of the tension stud were so badly bent that the washer and beehive spring wouldn't even come off. I used a large-bladed screwdriver to pry them open wide enough to slide everything off.

At first I pried them too widely apart, so had to use pliers to bring them back together. Whenever you use pliers on a threaded part, always wrap the part in a leather scrap first. If you damage threads with the teeth on pliers, you won't be able to screw anything back onto them. The leather gives you a good cushion but still provides grip.

Finally I got the parts off. I left the stud in the machine--easier than putting it in a vise, which I don't have anyway--and started trying to straighten it. I did this by alternating between prying them apart with the screwdriver, then closing them back up with the pliers. If you do this you'll want to be cautious and use minimal force, as the stud metal is quite soft and easily bent.

This required a lot of back-and-forth. Here I got the top piece nice and straight, but the bottom piece was wrong, and the overall stud was still bent slightly upwards.

Next I got the main shaft straight but the split parts going downwards.

Finally I got it to this state:

It's not dead-perfect, but it's close enough to get it working right. I've found that sometimes when you try to get something perfect, you go too far and mess the thing up. The sewing machine repair teacher Ray White taught us about knowing when to stop, and I listened. The important things here are that the pin inside needs to be able to smoothly travel in a straight line, which it now can, the split part of the stud needs to be parallel enough to cleanly get that thumb nut screwed onto, and that thumb screw has to be parallel with the discs when the tension is activated.

I put everything back together and eyeballed it. Everything seemed straight and parallel enough to try. (In this photo the presser foot is up, which is why the discs are angled lazily. I should've taken this photo with the presser foot down, which would show you the discs in their proper under-tension position.)

I oiled the machine up from top to bottom, cleaned out the feed dogs and hook area, then put everything back together.

Next I did the stitch-in, as I learned to do in Ray White's class, and got the thread balanced. Everything stitched great.

Here it is back at my neighbor's house, and yes, I put in a new spool pin. The duct tape one was driving me nuts.

I know this wasn't a proper tutorial--there aren't enough detailed photos and specific instruction--but if many of you have the problem of a bent tension assembly, let me know in the comments and I'll try to prepare one down the line.