I don't know if I have a similar machine but mine has the long bobbins and heart shaped piece like you've described. To fill a bobbin on mine...place spool of thread on machine...go through the first thread guide...I go once around the tension disc backwards so that the thread end is in the right position to go to the bobbin winder. I place the bobbin in the bobbin holder. I run the thread under the little wire and through the 2 thread guides and I put the end behind the one end of the long bobbin. I then loosen the silver knob in the middle of the wheel (towards me) this keeps the needle from going up and down as you wind the bobbin. I then tip the bobbin rubber wheel towards the machine until just touching. If you push it over too tight it makes it hard to treadle. After all that..... is it the screw in the middle of the heart shaped disc or the screw on the bobbin thread guide that tightens? I've never had to touch either of those on mine. There is also a large knob right below the bobbin winder on mine. That knob is for shortening and lengthening your stitch length and should not effect filling the bobbin.