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:    • How to: Change auxiliary belt & pulle...  
* More on the belt tensioner:    • Auxiliary belt tensioner, noise & aft...  
* Water pump:    • How to (fail): (Nearly) replace water...  
* Overrunning alternator pulley (OAP):    • How to: Test & replace overrunning al...  

Amazon links for the Duratec HE (check your part no.s):
* Serpentine belts & pulleys ~ US: https://amzn.to/2Gugnmh | UK: https://amzn.to/2GLgt8o
* 6PK2225 as featured ~ US: https://amzn.to/2TNQpNC | UK: https://amzn.to/2tpyl0v
* Idler as featured ~ US: https://amzn.to/2BCt0aW | UK: https://amzn.to/2IgAQg6
* Tensioner featured (Continental # 49405): https://amzn.to/2VFScG2
* More tensioners ~ US: https://amzn.to/2S6gW6R | UK: https://amzn.to/2SFdgy6
* Water pump ~ https://amzn.to/2XLTdfC
* Or, for generic pumps the Ford part # is 1142427 ~ US: https://amzn.to/2ZCqbAS | UK: https://amzn.to/2W5qSAE
* Alternator overrun pulley, try searching ~ US: https://amzn.to/2lvN0H6 | UK: https://amzn.to/2lvSVfr

More detailed links for tools etc are in the specific videos above.

Using the above links helps support my channel and is appreciated!