Ok update gents, at idle it is there either cold or warm. Then if you slowly give it gas it will go away then I can rev it up and when I let go of the gas it’s loud but then quiets out at idle.. Seems to tick with motor though. I’m thinking maybe pulling valve cover and ensuring rockers are tight? Any other ideas we haven’t explored? What would go away when under load?

 

Could we get a video ? Everything is currently a shot in the dark .

 

I'm mostly at a loss here but.......I believe it's just one of the mains that controls forward /rearward movement of the crank. How could I knock like that for 100K? The thrust bearing might be "clearanced". If it were a rod I'd expect more trouble. With age and a little "taper" or "bias" might a crank (thrust) one way or another producing a knock, but last forever without the thing failing in a very unwelcome way?

BTW, from what I gather water should work as well, or better than Seafoam. (gotta figure seafoam does contain water)