3.8 Noise... Timing Chain/Dampener? (Hopefully!)

[DieselMechanic]

The Bonneville was Duramax powered for a while today.


I thought I might have heard a slight noise a while back while under the hood of my car down around the water pump area, but kinda disregarded it.

Yesterday morning after a pretty harsh WOT pass, I turned into a gas station a few miles later and heard a terrible knocking noise, so I immediately shut it off and hauled it home on the gooseneck this morning.

Oil pressure is perfect at idle and there is no miss to it, started perfect.

I did notice today when I started it to pull it onto the trailer, the noise was nonexistent exept for a "loose rattle" noise right at startup, if that makes any sense. Then after it ran about 30 seconds or so, I could barely hear it beginning to make noise again just before I shut it off.

Sounds as if it's coming from the front/center of the engine. This sound like a timing chain or a dampener guide?

I'm sure I'll be able to figure it out, but honestly never worked on a "sideways" or fwd vehicle before. Hell, this is the first car I've ever owned in my 30 years. LOL Always had trucks.

Any tips to tearing into that area?
Also wondering, if I end up replacing it altogether, would it be easier to drop the entire K-member with tranny and all? Or to pull it from above?
I've got a pretty nice place to work on it, and a descent engine hoist.

[00Beast]

First, most important question: Does it only happen at idle?

Sounds like a dead ringer for a bad harmonic balancer.

[crappiefisher]

2 fast tests...engine off, can you turn the belt system at all? any play either direction makes the balancer suspect.

then, remove the belt from the crank pulley, secure it out of the way and start the engine for a few seconds, is it quiet now?

A bad balancer sets up quite a racket, and replacement is the cure

[DieselMechanic]

First, most important question: Does it only happen at idle?

Sounds like a dead ringer for a bad harmonic balancer.

Hmm honestly, I'm not sure... IIRC, I think I gave it a little gas and the noise was light along with it. I will have to check it out tomorrow.

2 fast tests...engine off, can you turn the belt system at all? any play either direction makes the balancer suspect.

then, remove the belt from the crank pulley, secure it out of the way and start the engine for a few seconds, is it quiet now?

A bad balancer sets up quite a racket, and replacement is the cure

I haven't tried turning the belt system... I did remove the belt and start it, however. Noise is still there.


God I hope it's a balancer... This is the worst time possible for this thing to take a crap on me! lol

[J Wikoff]

If the rubber is gone, it can rattle without the belt on at idle too. It's been a while, but I think mine did.

[willwren]

It will clatter with or without the belt if it's the dampener (harmonic balancer/dampener). But it will shut up for a few seconds if you lightly roll into the throttle.