No disrespect intended towards Peter, when I say that perhaps the piston was 180* out from proper orientation. So hard to know, since the piston top could have spun when things came apart.
The arrow on the piston points roughly 80* to the right from forward, which means it could have spun 120* from rearward. The intake and exhaust valve reliefs appear to be identical, so it would be an easy mistake to make, if a person didn't spot the arrow. Again, no disrespect intended.
