Hi guys,
I adjusted the CB550 while it was running by loosening the 10mm nut just enough so I could turn the slotted screw a bit to reduce cam chain noise and set tension. Not enough to be ridiculous like a hammerhead, but I used common sense.
For some strange reason, the cam chain noise subsided and the bike runs totally fine and tension is quite good.
I think Honda put that slotted screw on the tensioner so EEs and MOT inspection station guys would argue and belittle anyone on a forum about it 30-50 years later. But, hey what do I know? I'm just a costco guy.