Sponsored Links (Register now to hide all advertisements)
A real stumpper. Since you have taken the engine apart have you tried listening for the knock with the cylinder head removed and using the starter to rotate the engine? You said that the knock is more noticeable at idle so it might show up using the starter to rotate the engine. With the head off the starter should be able to turn the engine faster than with the head on. Plus you can see some of the moving parts.
Just a thought
Bob