The idea is that the slipper blade, idler blade makes a significant contribution to the amount of tension in the cam chain and also holds the chain (hyvo) in better contact with the cam wheels.
This bit threw me:
"What ever you do, dont take off the cam cover with the cam chain under tension. But definitely dont put it on when the same condition exists."
I'm assuming you mean had I been fiddling with the tensioner - rather merely taking off the cam cover - otherwise how would it be possible to check valve clearances?
When you remove the cam cover the chain should still be in tension and as you remove the screws from the cover the tensioner will try to take up the slack. If you hold the cover down hard till the last screw you may get away with it but if the cover lifts off unevenly whilst still undoing screws you could break the head at the entry point for the remaining screws.
OK unlikely but possible.
In reverse; when you have removed the cover and rotated the engine to check the clearances the idler blade is not present so the chain tensioner will take up the slack and make the top run of the chain tight.
Replacing the cover after this will put another 1/2 inch of tension into the chain and since the double taper lock on the tensioner is designed to resist being made to release backwards, you would crack the cam cover as you screw it down.
Needless to say; far more damage likely if like me you refuse to be beaten by something that refuses to go back where it just came from.
I am sure you knew this but thread headed off in a particular direction and i wasn't sure what you had done so far in the sequence of events.
Simple answer would be to remove the cap, spring and cross slide from the tensioner before you go in.
AL