Okay, ladies and gents...I'm tearing into an old treadle that was given to me. It's a Singer 66 model. Bought a new belt but it keeps slipping off the hand wheel. If I hold my finger to the back of the machine as a guide to keep the belt on, it will stay put. Is there supposed to be some kind of guide there? Since my other 66 is electric I'm lost as to why it would fall off there? I tried to watch to see what the deal is, but I see nothing wrong. Can anyone help?