Hobbsy, I don't follow your logic here. The only thing that determines the path of that valve in opening and closing is the valve guide. Assuming the guide is in its proper place in the head and the valve is not bent, there should be no way for the edge of the valve to touch the side of that relief. Timing can't affect the path of the valve. If you rotated the crankshaft and held the piston at TDC manually, then removed the valve spring and keepers and manually moved the valve up and down, it should never touch the side of the relief where that mark is. At least that is how I see it. I could be wrong, but I can't visualize how a valve with a straight stem could strike the side of its relief. The valve head can't move laterally as it ascends and descends. Maybe I'm seeing the picture wrong.