ArchaicArcane

It really comes down to the fact that I had nothing (or at least very little) to lose. They were both unusable machines as they sat.

In my "real life" I'm trained to follow a logic process (computer geek) to solve a problem, so this was pretty much just applying my training to sewing machine repair.

Tension has been my problem for years. (Not just the stuff between my shoulders either!) It's why it was the first post I made here. I started sewing when I was 10, and the machine (a 290C) my dad bought me for my birthday was in the shop more than it was out, but I still think to this day it wasn't because there was something wrong with the machine, I think it was because the operator never learned how to operate it correctly.

I used to run into a tension problem, and immediately be frustrated, and usually quit. (Of course at the time I didn't know it was a tension problem, I just knew there were nests under the needleplate, multiple threads wrapped around the bobbin case, and sometimes needle shrapnel flying at me.)

I've made it my goal to not run from these issues anymore, and in fact dive in head first and fix the harder ones (like these 99s dealt me)

Yeah, remember when it used to yield hits other than ebay, amazon and worthpoint?

I've got it set to about the width of my test thread. It slides through, but doesn't have room to flop about. I found that if it was too tight, it made a snapping noise when the machine ran, and if it was too loose, the needle thread tension was completely messed. So if it's sewing, and not making loud snapping noises every time the needle thread pushes through there, it's probably pretty close.

I used a tiny blade screwdriver, loosened the screw, pushed it around a little, then tightened the screw. There's a pic of that sort of in the tfsr manual. Page H-4
"The lower bobbin area"

I had to go at it in 3 different sessions. I found the problem the day after I got the machines, and made a note to fix it when I did the cleaning. Cleaning day I figured out it was not a simple fix (that's when I found the 2 tension extremes), then the 3rd day, I was just tired of it hanging over my head. Sometimes it works better that way, just step away, instead of getting frustrated. Took me 15 years in IT to figure that one out.

Use what you have, eh? I bought the scale for baking, and have an over abundant supply of those berries, so it made nothing but sense.
If I read Joe right, the spring he's asking about is the one on the bobbin positioning finger. If that's the case, on the 99 it's actually regulating the needle thread as it comes around and grabs the bobbin thread. That's why pushing the spring too far away from the bobbin case caused my needle thread tension to go haywire. I can post a pic if needed.

Otherwise, all of the principles are the same.

Part of the noise definitely comes from the fact that the bobbin case can rattle around a little, and does when the thread passes through the check point, there's the noise from the "check" as well, other than that, I'm not sure.

Yeah, I spent a lot of time watching that mechanism work in the past few days.