SOURCE: Thread looping on bottom of fabric, and bunching up around bobbin

Pull the thread through the tension assembly and test it to make sure the tension is working correctly.
(To do this test, adjust your tension setting to normal or medium or 5 or something in the middle. Raise the presser foot and pull the thread through the tension. It should pull easily!! Lower the presser foot and pull the thread. It should pull noticeably harder.) If it passes this test, continue up through the take up lever,then down through the thread guides to the needle.
If it passes this test you need to remove the bobbin case and check for burrs or rough spots. If you find any ,use an emery stick to remove them and then buff the area with fine steel wool.Put the bobbin case back in ,check your bobbin(change it ) and try again by turning the handwheel slowly and watching to see where thr thread is snagging
sewman7

SOURCE: Singer Simple bottom thread is loose

hi there
raise pressure foot up thread making sure thread passes between thread guide this should solve problem never alter bobbin tension,
mary h

SOURCE: Thread catching and bunching up in bobbin latch while sewing

I had the same problem where the thread was getting all bunched up on the underside. I took everything out and followed the manual concerning threading, then manually moved my right wheel to see if it would get bunched up. It took awhile, but I finally got it sew correctly again. I;m still not sure what was wrong with it. I have a singer 7470.

SOURCE: Touch & Sew zig-zag model 758 - bobbin thread

email me for retiming instructions and remind me of your make, [email protected]

SOURCE: Singer Sewing Machine model 9224. Bobbin thread

If you turn the handwheel, can you see a metal ring rotating around the outer edge of the bobbin case? If not rotating, broken gear or timing belt off.
If that ring is turning, remove the needle plate and bobbin case. As this ring now rotates, you will a finger on the ring that will pass behind the needle from right to left and it should catch the thread from the eye of the needle. If this finger, the "hook" passes above the eye, you have a timing problem.

Let me know.