We may have found other answers which could help you.
Click here for Sewing Machine Bobbin NeedlePresser foot is loose?
how to get the tension right on my machine?
Singer zigzag 457 Stylist not threading bobbin/making stitch?
1965 Singer 275k sewing machine foot pedal?
Singer 507?
My CG 500/550 Singer Sewing Machine's bobbin isn't working?