Q: What causes big loops of top thread on the back of the quilt?
A: If you’re seeing this, it’s helpful to know what the size of the loops are – I’m guessing they’re around ½” of thread, and are pretty consistent. Most people would blame the bobbin, which is not the case in this situation. A badly wound bobbin, bad antibacklash spring, or using a bobbin genie would not cause or fix this issue. You’re seeing excess top thread, not bobbin thread.
If the loops are a little larger than ½” of top thread, the rocking finger might be the cause. Before you do so much as one more thing, power down the machine!!! The safest thing would be to actually unplug the machine.
Hold the top and bottom threads at a 9:00 position on the needle plate. Track down your bifocals and look in the hook area. Hand walk the hand wheel around (turn it clockwise) while watching the thread move across the face of the bobbin case. If it snags on the rocking finger (the small finger located at a 6:00 position that taps a little tab on the hook assembly), you’ve got your answer. It’s possible the rocking finger was bumped and is not properly positioned/timed. I’ll talk about how to fix this in a later blog post.
If the thread easily slips past this area, you’ll need to take off the needle plate to check the next probable cause. This is a good opportunity to get out your vacuum and a brush and do a little housekeeping. Note: I DO NOT recommend canned air!
After removing the four pounds of tightly packed oil soaked lint found in many machines, again hold the threads as discussed above at exactly an 8:30 to 9:00 position. Hand walk the wheel. As the thread travels around the front of the face of the bobbin case, watch carefully as it clears the small gap between the retaining bracket and the notch in the hook assembly at the 12:00 position. The retaining bracket is black. The small protrusion of the bracket that fits into the notch on the hook assembly should be in about 1/3 to 1/2 of the depth of the notch. If the thread is catching here, the retaining bracket is in too far for one of two reasons: it was bumped and pushed in (perhaps because it was not properly tightened down), or for some reason the hook is further forward than it should be, which will cause the needle to be pushed forward as the hook passes behind the scarf of the needle.
If the timing is OK (the needle is not being deflected forward at all), then the retaining bracket needs to be adjusted.
Grab a flashlight and either a good screwdriver or your metric Allen wrenches (depending on machine age). If you look from the floor up into the bobbin area, you’ll see where this bracket is screwed in. Loosen the screw, reposition the bracket and TIGHTEN the bracket in place. This could be a two person job. You DO NOT want this to move ever again as it can be pushed out and really cause some damage as the entire hook assembly spins out of control. Test again by hand walking the wheel while watching several rotations. If you are confident that everything is OK, replace the needle plate and put all four screws in loosely. Again, hand walk the wheel until the needle is in the lowest position. Center the hole of the needleplate around the needle, then tighten the screws down. Test the stitch quality to make sure the problem is resolved!