We may have found other answers which could help you.
Click here for Sewing Machine Repair Instructions
the thread is bunching on underside of fabric it looks like birdnest?
Singer zigzag 457 Stylist not threading bobbin/making stitch?
Singer 507?
Presser foot is loose?
Singer 201 went bang , smelt and now won’t work?
My CG 500/550 Singer Sewing Machine's bobbin isn't working?