I realize that it is overheating because it is nocking soon after start. Higher octane, (98 instead of 95) and extremely rich mixture helps a bit - I can ride 5 km but then it starts knoking heavily. I have found that krankshaft oil passage most likely is cloged and oil doesnt get through connecting rod bearing freely, although bearing itself looks ok. I can barely push carb cleaner through it and flush oil doesnt' go through it at all. So I'm fixing that, and yes - I read now that aluminum oxyde is quite termal conductive. Well it will look diedier now, just thinking how to get rid of these corundum and possible sandpaper particles. Cowling is fine and fan blades are intact. Head gasket - which one? The metal one that goes between cylinder and head, it is new, I put it last year. The rubber one for valve cover is leaking a bit, but I didn't realized it may be overheating problem? Surely I'll fix it this time. Thank you for your replays.
p.s. oil preasure was ok before oil flush and engine dissasembly. Oil pump clearances are well within limits too and the rest of oil passages are ok. Yet I've found thin long metal shavings aside plain bearing of the crankshaft, on the flywheel side. Bearing itself shows streaks of brass. Fiew small brass particles were in coarse oil filter too. Transmission side bearings are ok, no visible damage. Inside cylinder there are marks that I red maybe water damage (image) smooth to touch, expet one spec that can be felt recess. I got this engine last year as engine swap, I have some history of it but it's owners riding style.