I don't know what kind of plug it was but it didn't have an idle bar. The threads in the head appear to be ok. I was actually coming over the runway when the engine started to sputter, so thinking I was getting low on fuel I turned around and the engine died. So it was running for I'd guess 15 seconds from first sputter to when it quit.

The bearings appear to be in good shape, a little rust but that's all. Once I removed the piston/sleeve, the crankshaft felt pretty smooth before I removed it.

Do you really think just running lean could cause this? I'm pretty sure it was running fairly rich. It looks to me like it swallowed a steel bug!

Piston/ring and new head = $80.