That scoring was caused by more than just the engine running "a bit lean".

Though the picture is very blurry, it appears that something fell into the combustion chamber and then lodged between the cylinder and wall.

Did you use a fuel filter between the tank and carb?

Did you filter the fuel when fueling the plane as well?


I've accidentally run engines hot and lean to the point of siezing, and the damage was not nearly as bad as that.

If anything I merely returned the engine after it cooled down, and started it right up again w/o any problems.