I have a '47 FW that I love. Last night I took the throat plate off to clean out lint. This morning when I started to sew, I forgot to pull up the bobbin thread and it started making a knocking sound. I took the thread out but a piece of thread was hooked around the bobbin casing. It was really stuck and I removed it... with some tugging. Now the hook is moving around freely. I've done something..... Can anyone tell me what to do to fix it? I have a repair manual but don't know what is wrong?