OK, here's some more on what seems to be going on. The top thread seems to occasionally (I haven't figured out if there's a pattern to when yet) get caught between the shuttle frame and the shuttle, on that piece that goes over the top of the bobbin. See the video. Anyone have any ideas what might be causing this? Is it a tension problem? When I look at the parts diagram that Uwe linked to above it shows a very tight clearance between that arm and the shuttle/bobbin, and mine is much more open (see photos). Is this the problem?
All suggestions welcome!!!
47K5 Shuttle Frame Catching Top Thread.mp4