KraigThomas

Noise recently started on 2008 Denali at 130000 miles. Noise is still there after temporarily removing all the belts. Timing chain cover was removed but nothing unusual was found. https://www.youtube.com/watch?v=rwBMaTx4hy8

KraigThomas

This L92 engine does not have AFM

07NBSChevy

iTrader: (1)

There is a Bird Chirping in your Airbox haha.

Is the sound more definite on one side than the other? Can you also get a video from the topside of the engine.

So you have removed the Serp. Belt with no change, you removed the front cover and inspected timing assembly and all looked well.

It is very hard to say with the limited info thus far. I sounds very familiar to my work truck that had loose flex plate bolts. Have you listed to it from under the vehicle near the flexplate/torque converter?

KraigThomas

Here is a video from the top.

I can't tell if the noise is more on one side or the other. The noise seems louder when you stick your head under the vehicle, just behind the front wheel.

07NBSChevy

iTrader: (1)

In that video it almost sounds like a single rocker arm trunnion has failed. First thing I would remove the valve covers and check the play in all the rockers. If you can connect up the coils somehow, have someone start it with the passenger valve cover off and see if you can pinpoint the noise, then move to the other side. If nothing, lift vehicle and slide under it, remove those plastic side covers on the engine that cover the torque converter using a 10mm and listen there while running.

That seems like it may be the next steps.

KraigThomas

Measuring the frequency of the noise I notice it is at approximately 300 chirps/minute. Does that point us to the components moving with the cam rather than those moving at the rate of the crank?

G Atsma

300 /minute would be cam frequency at idle, assuming 600RPM idle. As said above, check for bad trunnion bearings.

KraigThomas

Update: The noise has reduced. At times I can't hear it at all, at start up I hear what is less of a the chirp I heard before but more like a tap. Same frequency as before.
I've done a bunch of stuff:
1) Pulled the valve cover off on the side that seemed to be noisy and couldn't see anything that looked wrong. I could not notice play in the rocker arms.Took it to a mechanic who did the same...he said it was something deeper than the rocker arms..
2) I changed the oil and put in a quart of Marvel Mystery oil. Nothing changed
3) I took the valve cover off and tried to clean out the oil passages through the push rod and then hopefully through the lifter. I blew compressed air through the holes of the back 4 on the passenger side. That's where is sounds like the noise it is coming from. Then I sprayed B-12 carb cleaner down the holes. Also bought a 35 cent hypodermic needle from walgreens and filled it with B-12 multiple times and injected it into and down the holes in the rocker arm/pushrod. Noting changed.
4) changed the oil again but this time I added 1/2 quart 2Xconcentrate Resoline to the fill. Started the engine and there was no change. Decided to drive it to the auto part store to get something else and on the way it started to get quieter. By the time I got to the store it was much quieter so I just kept driving. Drove for about another 1/2 hr. By that time it was hardly noticeable.
So now when I start it up I get the tap..tap sound, but once its up to temp for a bit the noise is pretty much gone. If I listen close I can hear it some times at temp and some times the noise is completely gone.
Do I have a lifter with an oil port that is partially clogged, as the engine warms more oil can get through the hole and give the lifter its full length?