Metal shaving is aluminum from the chain guide frame. When the plastic disintegrates the aluminum frame will start to shred. Also when the chain eventually derails it will chew up the chain cover also aluminum.

Compression comes from crank turning not cam moving. If cam not moving you can have or not have compression depends if valve is permanently open or closed (or bent= open).
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2011 E70 • N55 (me)
2012 E70 • N63 (wife)