90k miles. Only other issues are a busted AC and the common VTC rattle, which sounds a little different perhaps. Not sure if they're related, gut says so.
This sounds a bit like a horse galloping. It goes at about 400+ RPM, so about half what the engine as a whole is doing. It is irregular in its beats, and there is a mixture of more clopping beats and metallic slappy beats, with the latter less common. Hard to pinpoint, but it seems loudest nearest the center of the top engine.

I replaced the chain tensioner, but it made no difference.

Video attached.

 

i valve grossly out of adjustment ? or 2?...half RPM...id check valve adjustment...CHEAP check...my valves rattle on cold starts now ...does go way....does it go away ???....id say no.....OR piston slap?....probably engine DONE on that one,but it should go away when hot

 

With 90,000 miles you should have had at least one valve adjustment done.

Go to your local Honda Dealer and get a valve adjustment right now!!!!!!!

Don't wait!!!!!!!!

 

yea...60,000 KMs and i shouldn't wait either....ugh, unbolting the plastic valve covers....will I???

 

I'll be taking it in for an adjustment and general look-over, thank you everyone. I'll report back afterward.

 

Got it back: that was not the issue. But it does run a bit smoother. But it's still clanking.
Take it to someone else to diagnose I guess.

 

Groan....i sense you didn't go to the dealer.

i would have got a horrifically overpriced valve adjustment and mentioned the clanking....but i sense we are past that.

i would go to dealer and pay horrifically overpriced diagnosis fee.

does it clank all the time, consistently, no matter what load or temperature the engine experiences? ????

after listening to the video 100times id say the exhaust piping is loose.

put your hand behind or ideally under car, does any piping or bolts or HEAT SHIELDS feel loose ?

when you first start cold car, does your hand feel any exhaust leaks ?

i thing an exhaust coupler is loose and thats the clanking...OR a head shield

 

https://www.fitfreak.net/forums/3rd-...d-bracket.html

??...could this be it?

 

Eventually it was diagnosed as a bad AC compressor. Also the AC doesn't work. Makes sense.

 

Huh,,,,,good to know, thanks