I pulled the head today to see what the damage is.
There is a definite mark across the straight edge of the Exhaust valve cut-out in the top of the piston:
(Ignore the sideways scratches, that was me with a fibre rod down the plug hole the other day to show when the piston was going up and down)
And a corresponding mark across the Exhaust valve head.
Note the valve has spun round:
The easiest way to see if there was any gaps between the valve head and seat was to turn the lights out and shove a small pen torch up the Exhaust port to see if any light escapes:
Then spin the valve round 90 degrees to see if the light leakage moves, which it did:
And then the light can't be seen with the mark towards the camera.
