Loud *clank* sound from engine - 2007 Tahoe 5.3L

[iamdub]

Your first post said it sounded like someone hitting the engine with a small hammer, so I was thinking it was a steady "bang bang bang bang bang" and not just a single "bang" ever so often.

I wonder if it does it when the A/C compressor clutch engages?

 

[hound_dog]

It's very possible that it's the AC.
Today, I took a 15mm wrench to the tensioner to remove the serpentine belt. I was able to freely spin each (except for the crank of course and AC since that's a separate belt). There was no play and no roughness so I reinstalled and rehooked the battery.
It started right up and I got the "clank" sound after about two minutes. Then another a couple minutes later...then no more for the next 5 minutes (nor the rest of the day which was about 25 miles of driving). I'll try a slo-mo video tomorrow morning and focus on the AC compressor since it seems like it's coming from that area.

 

[Doubeleive]

if you just take off the ac belt then you'll know for sure if that is it or not, like I said I've had mine made some really strange noises before, one of them at idle would be fine perfectly quiet but upon acceleration it would sound like death warmed over, lol another just made random metallic noises clanks and bangs and sounded like was chewing up a tin can inside.

 

[Chubbs]

When I went to buy my truck, the dealer said that the AC would stop blowing cold. He said that the AC pulley wasn't turning true and after they had it shimmed, the AC worked properly. It has been working fine since I purchased the truck last April, but he warned me that it would need replacing down the road. He advised it was somewhat common with NBS models.

Was he referring to a faulty output bearing of the AC compressor, or is it something else? I have replaced output bearing of the AC compressor on a different make vehicle where it was mounted up top of the engine & that was a cinch. Same R&R on this truck looks like a PIA if it's even the same deal. Can somebody enlighten me on this "AC shimming" and is that even a thing??

 

[Fless]

if you just take off the ac belt then you'll know for sure if that is it or not...

^^^ This. Run it without the A/C belt. Stethoscope is a good idea, too, to narrow it down.

 

[hound_dog]

Thank you all for the AC belt idea, I will give that a try soon. I've tried to get videos the last 3 days on startup and it's made the noise twice each time but the video didn't turn out. Finally got one today. I recorded in slow motion but youtube didn't maintain the speed. The sound is just before the 14 second mark.

One other thought, if this is during activating the AC clutch, is there a fuse to pull that would stop it from attempting it?

 

[swathdiver]

On another auto, a tensioner would make a sound like that. Did you stick an extension in your ear yet?

 

[08grey]

Bent rod. Getting stuck.

Sent from my SM-G950U using Tapatalk

 

[hound_dog]

On another auto, a tensioner would make a sound like that. Did you stick an extension in your ear yet?

Not yet! I'll try that after removing the AC belt to see if that was the cause.

 

[hound_dog]

Bent rod. Getting stuck.

That's not a comforting possibility! Made it home today (222 miles) and will be calling tomorrow to get into the shop.