Chris,
You might have to take the bobbin case out and see if there is another thread caught underneath it.
There are lots of places to oil on the bottom of a 66, forgot a few of those myself. I was using mine last night it was very noisy, so I got the manual out and figured out where to oil on the bottom. Its much quieter now and sewing beautifully.
I got a purple onion award in the process of removing the belt from the treadle wheel, no belt shifter on this set of irons. I forgot that I have to undo the belt to take it off. I have a lovely bruise on the bottom thumb joint.
Sharon W.