[chrs1961815]

This can be a very difficult thing to diagnose. I would lean toward the rod bearings and makn bearings aa previously stated. Those things can really cause a knock. Valves that are out of adjustment - even way off have a different sound.

Something else you should try that has not been mentioned is verify that nothing is hitting the oil pan dipper tray. Look for any shiny marks. Also, verify that you have the thrust plunger in the timing gear cover and it is in good shape with no broken spring.