I have the 6600 and is now 7 years old. I have only experienced this problem two or three times over the years. I clean it every other time I put a bobbin in and put one drop of oil on the wick in the bobbin case about once a month or as needed. I also use bobbin genie, which is a teflon ring that goes inside the bobbin case that prevents the bobbin from jumping up and down. If your thread was balling up at all just above the needle, it means you needed a larger needle. I use topstitch needles only, as the eye is wider than other needles to help thread go thru more smoothly with less problems. Also, one point two dealers told me to do, is to never pull your spool of thread out with the machine threaded, as it goes against the purpose of the tension discs, causing problems with them. Cut your thread at the top, than remove your spool, and than pull the strand of thread out at the bottom of the needle. This insures the proper direction of the discs. Just some pointers. I love my 6600 and it has been a true workhorse. I piece and do lots of fmq with seldom an issue. Hope this helped....