I had an email from a reader who has a Kenmore 158.1561281. It's jammed. It sounds like a thread lock. It occurred to me that perhaps folks don't know how to get the hook out of this type of machine.
When I bought my mid arm Bailey (http://www.baileyssewingcenter.com/homequilter.html) Mr. Bailey taught me how to take the hook out and put it back in. This step is necessary every time the bobbin is changed because so much lint can build up and he recommends oiling the race every bobbin change. "Complete the circle" was his way of explaining how the hook goes back in. Perfect.
First you have to get the hook out.
On the free arm it is easy.
Open the door
When putting it all back together, complete the circle
And replace your bobbin case. Be sure that the bobbin case finger fits into the notch in the race cover. It won't work otherwise.