I have a Kenmore sewing machine purchased in 1975 or 76 with unknown model #. It works fine except I can't get the tension regulated. I have adjusted top and bottom tension in every setting. I was able to get it to sew fine on one thickness of fabric but it messes up when sewed on double thickness. I have changed needles, completely cleaned and oiled machine, made sure threaded properly, checked and cleaned the bobbin mechanism, checked presser foot tension all to no avail. I'm now wondering if it is the bobbin case that needs replacing. I would appreciate any help. Thanks
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Hello and welcome to the forum!
What's it doing exactly? Is the top or bottom thread or both that's not right?
Did it just start recently or is it a new to you machine? Is it doing this with all fabrics?

 

Both the top and bottom threads are not right. The top thread looks right until I turn it over and there are loops, some small, some larger, depending on where the dial is set. The bottom tension is very tight unless I loosen the screw on the bobbin case. That's why I have been adjusting both of them. Yesterday I did get it correct on a single thickness of fabric, but when I doubled it, all the loops came back. I haven't used the machine in a few months, but the last time I did, it sewed fine. I have had this machine for years and have had to adjust the tension periodically, but never have I not been able to get it regulated. When I sew it globs up on the bottom and the machine slows down. I have been working on this for hours, so I might have messed up the whole works. I haven't tried it on any fabric except drapery fabric. Thanks for your help.

 

The thread you see on the top of the fabric, is actually your bobbin thread, and the thread that's bunching on the bottom, is your top thread.
Are you using good thread like Gutterman? Cheap thread can cause problems and if it's old, it'll start to deteriorate. Also check your needle plate and make sure it's smooth and the thread isn't getting caught on a burr or a nick.
Get the thread on top of the fabric looking right, then just concentrate on the top tension knob.
Also, sometimes the tension mechanism needs to be taken apart and adjusted or the timing could have gotten out of whack, either of these probably need to be taken in for repair. Sometimes it's worth it, as the old machines are good machines.

 

Thank you all so much. You have been a great help.