Well I think I've got the answer! It looks like the connecting rod is scraping against the piston skirt because the cut-out on one side of the cylinder skirt (to allow the connecting rod to pass the skirt) was not cut out properly. (So as the big end is moving from 6 oclock to 9 clock and then from 9 clock up to 12 oclock, the rod is getting locked up by the edge of the skirt.) I'm going to take a dremel to that point on the cylinder skirt tomorrow and hopefully will have good news to report. Thanks for all the ideas folks.