Engine was a transplant so I am not sure of the milage. But the con rod bearings were worn to the copper a bit on some so it must be pretty high.
the sound increases with rpm and gets less noticable at higher rpm but it is still there. ( maybe you just cant hear it due to ehxaust )
what is maximum piston to bore clearance?
I may pull the heads and see if there has been contack with piston.
any help appreciated.
Al