Okay, here we go.... Laptop live in the garage today.
In have pulled the head and jug, and the news isn't good. The lower piston ring was broken,and there's a large fragment unaccounted for.. it quite likely dropped into the crankcase, I see no sign of it around the work area.
On top of that, the piston and cylinder are both pretty badly scored from the second ring down in a couple of places. Here's pics pf the piston:
Intake @ right:
Pics of the cylinder next post.