'A shaft moving around'......
Not for long. The bolts will back out & there would be quite a bit of valvetrain noise requiring the engine to be stopped to investigate.....
And yet it went on long enough for fretting to occur. Fretting is cyclical, it requires repetitive movement between closely mated surfaces.
To summarize, 3/8 bolts can distort the shaft, but not bending from the increased moment of the loose shaft, and a loose shaft would increase noise to the point that immediate action would be taken, but also occur for so long to cause fretting in multiple locations on the shaft?
