Engine knock & rattle: accessory belt pulleys or engine internals?

After replacing the accessory belt and idler/tensioner pulleys, this Ford Duratec HE developed an annoying knock or rattle under certain revs and loads. It’s difficult to tell by ear whether a knock is coming from within the engine, or if it’s maybe a bad pulley. You can disconnect the belt from the crankshaft and run the engine safely for a short time, to identify if the engine is making the noise without the belt and pulleys being turned. More on the belt & pulleys ~ * Replacing the belt & idler/tensioner: * More on the belt tensioner: * Water pump: * Over-running alternator pulley (OAP): Amazon links for the Duratec HE (check your part no.s): * Serpentine belts & pulleys ~ US: | UK: * 6PK2225 as featured ~ US: | UK: * Idler as featured ~ US: | UK: * Tensioner featured (Continental # 49405): * More tensioners ~ US: | UK: * Water pump ~ * Or, for generic pumps the Ford part # is 1142427 ~ US: | UK: * Alternator over-run pulley, try searching ~ US: | UK: More detailed links for tools etc are in the specific videos above. Using the above links helps support my channel and is appreciated!