Pealing chrome on metal bobbins will do that too.

Joe

out of round or bent bobbins will too

I had problems adjusting a tension yesterday until I figured out the hook had a burr on it - no amount of adjusting tension was going to fix that one

I've looked at the hooks on each machine I have for burrs, and so far thankfully I haven't found any. But I've wondered just how in the dickens does someone stick something in there hard enough to put a burr on a hardened steel part. Sometimes you just gotta shake your head in amazement.

Joe

yeah - I've never caused one - I have gotten rid of burrs - seems like people pull stuff through

Thank you all for your help with this. I bought the new parts but didn't need them after I took your advice. Joe, you were exactly right that I just needed to take the tensioner apart and clean it good. I also took the bobbin case apart and cleaned it. While I was at it I took the entire bobbin fixture apart. I was astounded at how much lint there was. Only took about 2 hours (that tiny bobbin screw was a bear to insert) and the machine is now all back together and sewing beautifully again. I also looked at the original owners manual and discovered that the difference between a 15-88 and a 15-90 is that the 88 originally came with a treadle, and the 89 came as a portable with handcrank. This machine is definitely a 15-88 with the motor added at a later date. The treadle mechanism is all there and there are belts (newer ones) in the drawer. When the power is out I will disconnect the motor belt and put the treadle belt on. My Mom is overjoyed that the machine actually sews right again, so I won't be taking it home with me this trip!