Hey guys, just finished up my 220r cam install on my 2007 Classic Sierra, 4.8. I was freaking out because I kept hearing a knocking sound, then I noticed my belt tensioner, was rocking back and forth about 1/4 of an inch. The truck is not tuned yet, just finished the thing a few hours ago. Just wondering if this is just due to the idle bouncing around a bit? Or belt alignment? Thanks.

 

If the engine is surging or loping pretty hard, it could be. You may want to try a new tensioner anyways to see if maybe the spring is worn out. Does the crank pulley wobble or is it spinning true?

 

It's loping pretty hard without the tune, a from what I can see the crank pulley is spinning true.

 

I'd imagine it should clear up a little with a more stable idle. It is recommended to replace belt tensioners when you replace the serpentine belt as they do weaken with time (if yours is original, it's ~8 years old).