5.0 (Coyote) V8 .... knocking from accessory belt drive

[YukonTyler]

Had an odd one today.

 

2013 F150 with a 5.0. RO is written up as 'inspect for knocking from the AC compressor'. Interesting.

 

At idle with no AC clutch engagement there is a definite knock from the right front of the engine. Engage the AC and the knock is minimized - load related. I pulled both front accessory belts, ran the engine and confirmed that the noise is related to the belt drive.

 

With the belts off I felt all of the pulley bearings - the idler on the AC drive felt poor so I replaced it. No change. At this point I can still hear the knocking from the tensioner and idler pulley mounting bolts. Replaced the tensioner. No change. Also, there is no knocking from the compressor itself.

 

At this point I abandoned logic and began cancelling cylinders. No change. I devised theories about the timing drive components making noise under load and resonating through the front cover. Then I called a colleague over. He said that he has had two other Coyotes with this noise - root cause is tiny, tiny rocks wedged between the ribs of the belt.

 

I pulled off both belts, cleaned ~50 tiny rocks from the ribs, reinstalled and quiet as a mouse. That was a first.

 

[8WA Sman]

Every time I have had a belt with debris embedded in it, cleaning the debris out did not result in a long term fix. My theory is that if the belt material is soft it can allow this to happen again. I have also seen a noisy bearing cause shiny pieces to get in the belt, I think this is from the ball bearings or rust that builds up in the rotating assembly. I like to use silicone spray as a quick test to determine if FEAD noise is coming from the belt.