Harrishwhippets,
I clean and oil Singers 221 & 301's for customers and I get many machines that have the bobbin case positioning finger out of place. I had a customer that was fairly new to owing a 221 and she was sure that she had broken her machine; she hadn't lined the finger back up under the throat plate springs after she had delinted under the throat plate. She was so happy that it was merely operator error.
Sharon