The first three pictures left to right are of the same Gold Wing combustion chamber, and the same valve. This is why you want to keep a close watch on valve clearances on vintage Hondas, all models from the 60s on up through partway into the 1980s. They have valve adjustment intervals of only 2500-3500 miles for a reason. As the valve recedes its clearance is reduced, it gets less time to cool on its seat, and eventually it won't cool at all, leading to torching. The fourth and last picture is of a CBX1000 combustion chamber. Note the "pie slice" burned out of the valve. It's much worse than the Wing example. This customer kept riding the bike despite having only five out of the six cylinders working, so the burning is farther progressed.