We may have found other answers which could help you.
Click here for Sewing Machine Singer Repair Manual
My CG 500/550 Singer Sewing Machine's bobbin isn't working?
Singer 507?
the thread is bunching on underside of fabric it looks like birdnest?
Presser foot is loose?
Singer zigzag 457 Stylist not threading bobbin/making stitch?
Engine revving up ?