Hemming Levi's for husband. Using thick "jean" thread. Used 16 needle. Top stitch is perfect, bottom thread is anything but straight. I've re-threaded, cleaned the "hook", changed to a 14 needle. I still hear a knock and can't get a straight stitch from the bottom. What is wrong?

Hi! Sounds like you're doing everything right to me, so let's see.

By not getting a straight stitch on the bottom, do you mean that the bobbin thread is loopy? If so, then most likely you have to reset the tension. Get a scrap of jeans material and practice on that....it would be great if you could use different color threads on top and in the bobbin, but that might not be practical if you don't have the jeans thread in different colors already.

You'll be adjusting the top tension, because even tho the top stitch looks perfect, it may not be tight enough to pull the bobbin thread up into the fabric where it belongs.

Sew a couple of inches on your scrap, then stop and check the bobbin thread. If it's loopy, you can also see the top thread on the underside. (Which is why using two colors is helpful.) With the pressure foot down, tightened the top tension just a bit. Sew a few more inches and check again. Keep on sewing, checking, and adjusting until you can't see any (or almost any) top threads on the bottom or bobbin threads on top.

Here are a couple of other ideas to check:

1. Make sure your bobbin is inserted correctly. If I happen to put one in backwards by mistake, the bobbin will make a lot of clanking noises.

2. Using your flywheel, lower the needle all the way through the stitch-making process to see if it's hitting anything along the way.

3. Oil your machine.

4. Make sure all the screws etc on your throat plate (also called needle plate) are tight. (I've had mine get loose and that will definitely throw a knock into the works!)

Check out these ideas and let me know if anything works, or if the problem is still there, ok?

Happy Sewing!

Robbie