I took what for me was "lots of pictures' to help if I needed a memory nudge or even to look for something I hadn't registered at all when I was in the reassembly phase. I was more interested in getting the job done than photographing so this probably doesn't qualify as a real tutorial. It could help nudge someone in the right direction though, and might give you an idea whether this is something you would want to attempt on your own (Hint: if you totally screw up, you can eBay purchase the entire assembly for about $15.00. Cheaper than a Craftsy class. Go for it).
Elizabeth at My Sewing Machine Obsession had a lovely tutorial on newer model 158's, which at least clued me in to find the hidden set screw that held the assembly on. On the model 90, I had to open the door, to find it here:
As you might guess, it's in the middle hole, about even with the tension assy, not the holes top or bottom that line up with thread guides. Once you get that set screw loosened enough (and follow Elizabeth's advice, loosen don't remove to prevent loosing the bitty thing) the assembly just pulls/wiggles out.
Here's the whole assembly out. I confess I had to take it at least this far before I could buy a new one because the eBay guys had 2 types that looked similar except for the back posts. This one, I see now, is a short post. This is the point where you take note where things line up. I could see the broke end of the spring poking out with a straight line from top set screw hole through the spring exit point to the arrow that indicates the tension setting in front. I could also see that to get to that spring I had to make that bottom part come off.
Here it is at the next step. I didn't take notes, but I believe this happened just with pulling apart. You can see the slightly dusty tension discs that hold your thread there, good time to give them a thorough cleaning. I can't get to the spring yet, more disassembly required. This time, more tiny easily striped screws are involved.
In photo above I'm holding the back section that still holds the spring. One of the two screws is visible next to the diagonal mark on the cutting board. The two sections were held by those screws via holes indicated by vertical arrows.
If the spring doesn't pull out fairly easy, you may have to loosen the screws still in your last remaining piece. I believe there were two of the large size indicated in pic above, and three more that are really really small. Something like 3 threads wrap around those almost flat babies. Oh, and they are kind of soft and look like the little slot would love to rip up so it can't be used anymore. Careful not to over tighten when putting back in, and it is nice if you have a screwdriver that actually fits them. Once the spring was out I simply did everything in reverse until it was reassembled. I did wonder where to set the numbers in relation to the arrow for pushing back into the machine heat and at first had my lowest tension reading as kind of negative 5. I took it back out and set the arrow on 0 for a happy ending. Then I just checked tension by stitching and adjusted the bottom slightly.
A little cleaning and oiling for the heck of it. I stopped to admire the features on this machine.
The machine is from the very early 60's and is all metal. I don't really love the colors but I do dig the lines of it. The bobbin winder is ole-timey but neatly tucked under the door by the hand wheel and works very nicely, thank you.
My granddaughter asked me if that widow was the miles counter. It delighted me because this era did make machines that resembled cars. It's actually to set zig zag width. She does take cams (which I don't have) for decorative stitches, but does a basic zig zag without having to open and install. The round knob to the side of the zig zag width widow will decenter the needle to the left or right. Yup, that feature is nothing new, something I took for granted with any zig zag, though I believe it's a feature 'basic' machines might not have now.
The feed dog up/down selector is very accessible, and the machine does beautiful free motion embroidery and quilting. I admit I wouldn't want to wrestle with a large quilt in that small throat space, but it did some beautiful small pieces for me. It has a remarkably un-fussy tension. Matter of fact, it took light to mid-weight fabrics without issue even with the broken spring. I just thought the time would come when I'd need the check spring to do it's intended job with some slippery or speciao fabric or thread. The machine also has a presser foot pressure adjustment dial and I don't know what all other features that may impress, it was just a good solid machine.
Made in Japan. See the J-A4 stamped in there? Japan rocked machine making for American names like Kenmore, Wards, etc for many years.
After cleaning, oiling, and fine tuning I did a quick little sewing project just to show her some love.
Grandbaby jammies, shocking choice I know. I was very aware of how s-l-o-w this machine sews in comparison to my singer 201-2, and even the 401-A. This was one of the reasons my (11 year old) granddaughter loved it though. She feels more in control on it. It's still strong as only machines from that era seem to be. And the button- holer, sigh! It makes the button holes of my dreams, really really nice and really easy. It's almost worth keeping the machine on hand for those sweet buttonholes alone! Though the one I have for the 201 is close competition.
These beat out every other button hole system I ever had on (all newer, including top of the line computerized machine of the 90's) any other machine. A joy for both ease and professional appearance. I sewed my holes for more than 20 years without one of these, and can't stress how much I love these since discovery. Why did manufacturers stop making these, when they work so darn well?????
All in all, a long post because I'm glad to have this one back in the herd!