While you wait for answers, we may have found some information which could help you.
Click here for Model Machine BrokenSinger 507?
What size needles can I use for my Singer 39a3?
Singer zigzag 457 Stylist not threading bobbin/making stitch?
the thread is bunching on underside of fabric it looks like birdnest?
1965 Singer 275k sewing machine foot pedal?
My CG 500/550 Singer Sewing Machine's bobbin isn't working?