We may have found other answers which could help you.
Click here for Needle Hits Sewhow to get the tension right on my machine?
the thread is bunching on underside of fabric it looks like birdnest?
What size needles can I use for my Singer 39a3?
Singer 201 went bang , smelt and now won’t work?
Singer zigzag 457 Stylist not threading bobbin/making stitch?
Bobbin won't wind?