Quote: Why is exceeding 2000 rpm without load considered overspeeding?
Because it is stated in the manual.
HOW DARE YOU QUESTION SIKORSKY!!! (just kidding)
In my recollection from my training days I believe it is the short-shaft that needs to be inspected. It's the shaft that comes out of the engine connected to the lower pulley that you turn each way and listen if there is a clanking noise (metal on metal). Not sure why in a no load situation it needs to be checked.