Upper thread gets jammed in bobbin area

SOURCE: thread jamming at bobbin

Check to be sure the thread is not catching on the bottom of the bobbin. If it is, replace the bobbin because it is sprung. If it is not catching there, then you need to check your tension to see that it is working properly. Normal 0 MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman";}. Pull the thread through the tension assemblyand test it to make sure the tension is working correctly.
(To do this test, adjust your tension setting to normal or medium or 5 orsomething in the middle. Raise the presser foot and pull the thread through thetension. It should pull easily!! Lower the presser foot and pull the thread. Itshould pull noticeably harder.) If it doesn't do this, you need to remove the thread or lint that is stuck between the tension discs. Open them with a small screwdriver and clean them out.
If this doesn't solve your problem, remove the bobbin case and check the hook for rough spots.. If you find some, buff with an emery stick until smooth.
sewman7

SOURCE: a horrible tangle

This is a bit late, could the bobbin case not be seated properly? You need to put it into place and then turn it clockwise until it seats soundly in the opening. Also, check for burrs...the needle may have left a rough mark on the plastic or metal in the bobbin area. A piece of batting, or even an old knee hi should snag on any rough areas.

SOURCE: Upper thread knots up with bobbin thread when sewing a stich

Thread test
Test your thread quality to start, thread your machine and LIFT the presser foot (this opens the tension disks). Pull your top thread straight back. If you feel no tension no mater how much thread you pull, your thread is good. If that your machine passes that test, then let me know, we can go to step 2. If not, try different spool of thread, same test until you get a smooth pull (tip: always check your thread this way when you thread your machine)
Step 2:
Pull on your threaded bobbin thread while it’s in the machine. Does it pull smooth and even? If so, go to step 3. If not, try a new bobbin (bobbins get bent or distorted if wound too tight).
Clean thoroughly in the hook and bobbin case area and oil 1-2 drop is all.
Thread knotting on the bobbin can be a lot of things but here's some guidance:
Tension:
If the thread is loose on the bottom of the fabric, it's actually the top thread is too loose. Think of 2 little elves playing tug of war in your machine, one on toip and one underneath. If you have loops on bottom, the top needs to pull harder (tighten top tension)
Jamming bobbin case:
If it is damaged from turning out of place once, it could have rough spots on it that makes the thread hang on it, and keeps making it turn over and over. Use a finger nail board (fine sanding) and smoothall rough spots. Then reset the bobbin case taking care to put the notch in the bobbin case in alignment with the proper spot in the machine (basically 5 o’clock) when looking at the round area where the bobbin case goes.

SOURCE: thread knotting around bobbin case

hello, I had the exact same problem and could not find the solution until i took my machine to my sewing sensei and i solved my tedious problem. It was actually not a tension problem at all but a threading problem. Make sure you have threaded your bobbin correctly and that when you pull on the bobbin thread that the bobbin turns the right way. (mine must spin anti clockwise to work)  Make sure that when you pull up the bobbin thread using the needle that it is not over the feed dogs connective bar but under it. A big problem when the thread gets caught around the bobbin case wheel is that the thread is looped around the feed dogs once and that causes the thread to get caught around the bobbin wheel. In conclusion, thread the bobbin correctly and read over your instruction book before spending the money to get it fixe in s shop.

SOURCE: cotton keeps getting knotted from the bobbin

upper tension is wrong or upper threading is wrong (problem is always on the other side of the bunched thread)