Unless one has real good experience, one could never understand how illogical this whole picture is. I have been responsible for hundreds of 116/117 engine valve jobs. All due to chain failure valve/piston collisions.
Never is a long time for me, but if I have ever seen a burned valve in a 116/117 engine it would have to have been a pre 76 adjustable valve engine that had its maintenance massively abused.
The only possible exception to this would be a engine that had prior engine work that was done very poorly. I can't stress enough the reality of this motor. It just don't do what is said to have happened with a virgin motor at that mileage, not even double that mileage.
Bosch Master, ASE Master, L1
33 years MB technician