Wow, you guys are grabbing snacks and settling back into the side show that is my sewing machine? That's awesome. Keep snacking; I need your brain power here!
A few things:
1) The finger attaches to the underside of the machine bed, and there is no adjustment. It is fixed, period. (And yes, it is in correctly)
2) The machine is an oscillating hook, not a rotary one. (I am 99.8% certain of this.)
3) When the entire hook assembly is off (i.e. three mid-weight set screws on the shaft, removing the entire bobbin mechanism assembly), the machine turns freely; handwheel moves, needlebar and all sewing mahine guts move properly.
4) When entire hook assembly is replaced, but finger is off, machine still turns, needlebar, guts, and all, but hook assemble rotates fully as one unit; no oscillating.
5) When finger is added to the equation, assembly turns about 1 millimeter, (regular amount of built-in play for oscillation) and when it contacts the finger, and then the machine seizes. Handwheel continues to turn, but in a spinning-out sort of way. Needlebar and guts no longer move.
6) By the way, the "bopbbin race hook assembly unit" does not have any motion even within itself, whether on or off the machine. This seems wrong.
I hope this is all clear, I can try to post an annotated photo... we'll see if I am smart enough...