Bryanj, with all due respect, don't you think it makes sense to check the easy things first, just to rule out the usual suspects before we dive into the heart of the engine? There's not much lost by 1. verifying the rpm indicated are true, 2. the ignition is OK, all aspects, 3. the carburetion 4. etc. before we open the engine. I've gone trough the above mentioned rider's reports of CB500/550 owners again, in which they have listed all the repairs they had had. No one reported he had to renew the primary chain. Yes, they often make a noise, more often than not as a matter of fact, but here I am with mine with over 140.000kms. Yes, you can hear it. Does it worry me? Not really. It's not worse than when I bought the bike in 1980 and whenever mine is over say 1150 rpm, good driveability is present and that's what matters. If here in Holland someone had had that oil canal destroyed, I would have heard of it. You will remember that years ago I have volunteered to see to how far the chain will last. Realise that Honda continued the design up to the very last model, the CB550K4 in 1978. From that point of view, you will understand I advise to do the routine maintenance first. After all, blocked idle jets in the PD carbs the K3 have, is often the cause, as you yourself have reminded us of innumerous times. And it can make the engine sound horribly at idle.
Nobody can rule out something inside is wrong. The bike is 45 years old. Maybe it has run without oil, who knows? But the turbinelike sound I hear in the video when it's revved, sounds familiarly healthy to me for a K3.
The perfect idle some in the UK site strive for, is their choice. It nears a neurosis imo, but that's just an opinion. Some there will not give up before the engine runs like a switch watch. Well, I wish them luck. I use my bike for riding, not for sitting next to it in a deck chair to listen to its idle.
