I am also having problems with my big machine. Finally gave up and took the bobbin case to the sewing machine man. He doesn't think there is anything wrong with the bobbin case, but rather a spring is gone from somewhere in the machine. So, am taking it in for him to check, clean, ect, ect.
It is53 yrs. old and this is the first time I have had problems with it. I still sews like a dream and wouldn't part with it. Is a Japanese Singer and has sewn millions of miles!! The Featherweight is fine for now; suppose it will have a problem when I get this one back!!!(Take turns.)
Mariah