Loops on the underside often point to the upper thread not sitting correctly in the tension path or take-up lever. That is a useful first check, not a diagnosis of every nest: a tangle at the first few stitches, a bobbin problem, a damaged needle, or a jam can look different and needs its own check.
Stop and identify the symptom#
Stop sewing before pulling on a nest. Note whether loops form continuously under the seam, appear only at the start, or come with a jam, rattling, or needle strike. If thread is caught around the bobbin or shuttle, switch the machine off and follow its manual before opening the area. Do not force a handwheel or keep sewing through resistance.
Rethread the upper path first#
For underside loops, SINGER’s troubleshooting guidance directs the user to raise the presser foot and needle, then rethread so the upper thread enters the tension mechanism and passes through the take-up lever. Follow the threading diagram for your exact model: guides and spool orientation differ. Check that the thread is not snagged behind a spool cap or on a rough spool edge.
SINGER’s FAQ describes a brand-specific tension-path check: with the foot raised, the upper thread should pull easily; with the foot lowered, it should resist more. Use that comparison only where it matches your SINGER machine’s instructions. A change in upper-thread resistance can help show whether the thread is seated in the tension path; it does not identify every cause of a loop.
Check the bobbin and restart carefully#
If the upper path is correct, confirm that the bobbin is the type specified for the machine, wound evenly, and inserted in the direction shown in its manual. Check for loose thread, lint, or damage only in areas the manual permits you to access. Some machines have front-loading cases and others use drop-in bobbins; their paths and removal steps are not interchangeable.
Before testing, place both thread tails under the presser foot and toward the back if your manual instructs you to do so. Sew a short sample using the same fabric, layers, needle, thread, and stitch as the problem seam. Change one setup variable at a time so the result tells you something. Avoid turning a bobbin-case screw as a first response: lower-thread adjustments are model-specific and can add another problem.
When to stop#
If correct threading and bobbin seating do not resolve the loops, or if you find a damaged needle, persistent jam, unusual resistance, or suspected hook or timing damage, stop and consult the exact manual or an authorized technician. A troubleshooting article cannot inspect the machine or determine which of several possible causes is present.
For related symptoms, see bobbin winding and pickup and skipped stitches on stretch fabric. If the fabric does not feed or the seam puckers, consult your model’s manual for those separate checks.