We may have found other answers which could help you.
Click here for Plastic Top VerticalSinger 507?
Singer zigzag 457 Stylist not threading bobbin/making stitch?
the thread is bunching on underside of fabric it looks like birdnest?
My CG 500/550 Singer Sewing Machine's bobbin isn't working?
Bobbin won't wind?
What size needles can I use for my Singer 39a3?