Scaling down a rod for a large engine, a stretch of 0.15mm (each cycle) is nothing special.
The thermal expansion doesn't even come close.
But that's just the beginning, then there is crank flex, crank case flex, radial clearances etc. 0.3mm @ peak rpm isn't anyway out of the ballpark.
Add a misfire to the equation and things get really interesting.

So you aced every test but didn't get the grades... That makes about as much sense as asking basic questions when you say that you already comprehend the subject...
But is well within the norm of many engineers I've met, so please carry on...