Sorry if I sounded ungreatfull for your help.

It was just because this engine runs with variable ignition and knock sensors, so even though the compresion wuld be high, then the ignition would just retard the ignition to a point of where a preignition is not happening. its a M104 engine 3.0-24Valves (300E-24)

But i preignition could of cause also happen unpredicted but then not in al the cylinders and then the engine would run bad all the time wich is does not. (please correkt me if im wrong)

But it is deffently strange why they would brake a piece of them here and there.
The oil rings looked ok on the 2 pistons that we pulled out. I will will pull out the rest on Monday.