Since I'm not quite sure of what is actually happening with your machine, I'm going to tell how I understand how the stop motion clutch (the chrome knob) works. Holding the hand wheel with your left hand to keep it steady, turn the chrome knob away from you to tighten it. If you turn the chrome knob toward you, you should be loosening it so that you can wind a bobbin without the needle going up and down.
There is a washer in between the silver knob and the large hand wheel. It can be put on in four different ways. Only one of which is correct. I don't remember what the symptoms are for the incorrect ways. If you can unscrew the set screw on the stop motion clutch knob, the knob should unscrew all the way off to see the washer. There is page with a video about it at
http://vssmb.blogspot.com/2012/06/ho...bbed-stop.html Then there is a thread here about a theory about putting the washer in the correct position for a 201 which is a little different, but I think the theory may be correct.
I have a theory... I haven't tried it on any of my machines, yet.
There are three manuals at
https://ismacs.net/singer_sewing_mac...e-manuals.html that should work for your machine. The first three for 66 are the ones you want. You do
not need the 66-16 or either of the 66-18s.
Janey - Neat people never make the exciting discoveries I do.
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