We may have found other answers which could help you.
Click here for Singer Sewing Tophow to get the tension right on my machine?
the thread is bunching on underside of fabric it looks like birdnest?
Singer zigzag 457 Stylist not threading bobbin/making stitch?
Singer 507?
What size needles can I use for my Singer 39a3?
1965 Singer 275k sewing machine foot pedal?