Just buttoned everything up from my alternator and TB change and went to start it up and heard a tat-tat-tat-tatatata-tat-tat noise coming from the engine????? It ran fine except for the noise? Timing marks were all lined up and things seemed fine.... Had the wife start it while I was looking in the engine bay to double check and the noise is the accessory belt tensioner popping back and forth. Noticed a couple small marks on the edge of the new belt, nothing else irregular...

 

Would compression cause the accessory belt to tense up and flip its tensioner? I'm wondering if the little bit of slack between the exhaust and intake cams may have been taken up and created just enough of a difference in their timing to cause that kind of tension on every revolution? I'm at a loss.. Any ideas?

 

Tried reinstalling the belt? Not the timing belt, ACc one, unless it's out of alignment with the harmonic balancer, I can't see the timing belt altering your tensioner tho.

 

Christ, when I started the car and heard it my mind automatically went to "bent valves" and I **** my pants. Once I actually got under the hood and saw the tensioner bouncing around making that tapping noise I was somewhat relieved. From what I'm reading it may be the tensioner has gone bad from compressing it and having kept it compressed for a couple weeks while I waited for other parts etc... I am going to reinstall the belt when I get home from work and see if there is a way to test the tensioner with a torque wrench or something....

 

The car can run with the serpentine belt off. So you can remove the belt and make sure everything else is quiet.

 

So.... Pulled accessory belt and tensioner, checked that all of the accessory pulleys were spinning freely and made sure the tensioner was tight and all was good. So I yanked the timing cover and re-checked the timing. All lined up fine so I started the car without the accessory belt and no problems. So reinstalled everything and turned the engine by hand at the crank a revolution or two just to ensure the accessory belt was tracking fine and found that it was tracking over the outer lip on the alternator pulley. I first wondered if the place that rebuilt the alternator failed to properly space the pulley so started checking that all of the pulleys and rollers were aligned and everything looked good except the idler roller, which looks as though it has been bent up after years of abuse - like a wheel with negative camber. I am certain this roller not being true is what is causing the belt to pull off of the alternator pulley, causing the belt and tensioner slap that I initially thought were my valves bending when I started the car yesterday. So.... New roller? Or can I get away with replacing the bolt that mounts it? I'm still somewhat shocked the same thing didn't happen prior to this work I am carrying out.... Perhaps there was enough slack in the old belt?