Help- my one sewing machine is making very large loops on the underside of the fabric. It sometimes gets stuck and will not move a head. I'm talking like 1/2" loops. The top looks fine.

Do I need to oil it? Adjust tension? Bring it in to be serviced?

Help

Hi...what machine do you have....and have you checked the feed dogs are up, tension is correct, bobbin threaded properly and that you have no lint build up everywhere?

It sounds like your top tension is waaay off. Tighten it up and see what happens.

when mine does that,
I usually find a big lint ball.... or
Even when things LOOK to be threaded correctly... I rethread bobbin and top..... seems to fix it

There could be a lot of reasons why that happens.
First of all rethread your top thread. Take the bobbin out and put back in. Pull the thread out of your bobbin and start all over. Even if you know that you have done it correctly. Try another bobbin. If you have different ones, try another brand I once bought some cheapies and they work, but they are looser than the original ones and therefore I have more problems. Try diffent thread. Don't know if you have to oil your machine. That depends on the machine, so check your manual and see. Also make sure that the bobbin holder is sitting correctly. Take it out and clean underneath. I cannot remember ever needing to adjust my bobbin tension on my mechanical machine and it is getting pretty old. I do have to say that I don't put thick ribbon or thread in the bobbin, because then you might have no other choice. If I lived down the road from you I might have been able to help you out a little better.
Good luck to you and your machine

Ditto on the possible lint.

Like everyone said, re-thread everything first. And clean out any lint. Get a new needle too. Can't hurt. I bet you'll have her up and running right in no time.

when you have loops in the bottom the first thing i do is rethread the top thread it usually is because it pops out of the take up lever

Either your top thread is out of the tension disc or the tension is too loose in the top thread. Put in a scrap sandwich and adjust the tension tighter a little at a time until you get a balanced stitch. A balanced stitch will have the top and bottom thread meeting in the sandwich. Also make sure to check that the top thread path is free of debris in case that is effecting the tension.