There is definately some heat exchange on that piston.
I agree there is definately dirt ingestion, as there is light scoring across 180 degrees on the intake side of the piston, and from what you say gmax dirt ingestion was definately a problem. Dirt wont cause heat though, and with the discolouration in the piston there was another problem for sure.
My guess (common on this unit) is loose cylinder bolts, causing a partially loose cylinder which causes lean running (hence the heat)and also allows extra dirt ingestion to boot! It may have also been lean mixture settings, but there is defiantely heat exchanged in that piston
Gmax you are so right to highlight about air filters. It definately pays to wash and re-oil air filters correctly. The example shown above is a classic example where you can see where the dirt has by-passed. Was there oil in this filter foam? (for the untrained reading this, all foam filters are useless unless they are oiled)
