Is this the sound of rod knock?

[jeremiahm]

Good morning all.

2007 Yukon Denali 6.2 non-AFM all stock 203k on the ticker.

Been chasing a sound for months. Typically expresses itself above 30 under load. Changed the oil last night and decided to listen from underneath. Engine was almost at operating temperature and I hear this sound. What do you all think?

 

[Foggy]

I would guess from the noise flexplate bolts/ Flexplate cracked/ or just
a Starter.. Sometimes the starter motors go wonky on these and that's all
it is to replace it. You'll know once you pull the starter

 

[mikez71]

Is it noiser than the video under load?

Kind of does sound like knock to me, but I've never diagnosed/experienced it myself.
(except in an old air compressor)

 

[SpareParts]

Could be a rod, Loose torque converter to me.
Where does the sound seem like it's coming from? Does it sound like the rear, middle or back?

 

[jeremiahm]

While driving it sounds like its coming more from the right side at the cowl and it sounds like a baseball card in bicycle spokes. This sound has been going for about 8 months now, has become somewhat louder over that time. 30-60 mph it is very prominent and seems to go with vehicle speed more than engine speed and only under load (it has been impossible to successfully record the sound over all the wind noise). I am not sure if this sound and that sound are related. Under the truck last night is seems to be at the back of the motor and more on the left (non-starter) side. With a stethoscope i can faintly hear it most prominently around cylinder 5 when touching the oil pan flange. Don't hear it on the transmission housing.

 

[B-train]

I'd try a heavier oil first and see if it quiets down. If it does, then you have your answer. If it doesn't, then it could be something else mechanical.

But, to me it sounds like a rod, but timing chains can make a similar noise. How's the oil pressure hot and cold?

 

[jeremiahm]

Oil pressure cold at 60, hot idle at 25-30, hot on freeway 40. Did front and rear main seals, pickup tube o-ring and pressure sender three years (40k) ago. Here is a cold start 70° morning facing downhill a bit. This knock (maybe piston slap?) goes away after 15 seconds or so, again, not sure if it is related:

 

[Doubeleive]

Good morning all.

2007 Yukon Denali 6.2 non-AFM all stock 203k on the ticker.

Been chasing a sound for months. Typically expresses itself above 30 under load. Changed the oil last night and decided to listen from underneath. Engine was almost at operating temperature and I hear this sound. What do you all think?

you need a stethoscope to confirm where the noise is coming from, on mine the cat broke apart inside which sounded VERY similar.

 

[rdezs]

With your oil pressure readings, your rod, main and cam bearings are just fine.

Very difficult to say. Piston pin maybe? For starters I would do a compression and leak down test to see if that shows anything.

Then I would open up the engine to find out.
I would pull the front cover, make sure the timing chain tensioner is intact. They are known to break into pieces. Open up and inspect that oil pump as well. Then the oil pan to take a look at the bottom end. Check out the lower end of the cylinder bores for any evidence of unusual wear.

If you can get your stethoscope on the side of the block right at cylinder number five without burning yourself... That will probably narrow it down to a piston.

The notorious piston slap usually occurs on a cold engine and goes away shortly thereafter.

I definitely wouldn't be driving it. You might send a connecting rod through the side of the block. Or you could launch the piston up into the valves destroying your cylinder head.

The bottom line is sound travels in strange ways.

For what it's worth, I'm thinking either a timing chain or you're about ready to lose a piston.

 

[jeremiahm]

Thanks all, I will spend some more time with my stethoscope and inspect the t-chain for sure. No noticeable power loss over the last 80k miles I have owned it. Hard to not drive it when I don’t have another option.

 

[rdezs]

If you have the time, and oil analysis most likely would point directly to the component. The last one I sent into Blackstone Labs took just over two weeks though. If you have to drive it, I would drive it gently....

 

[Foggy]

Oil pressure cold at 60, hot idle at 25-30, hot on freeway 40. Did front and rear main seals, pickup tube o-ring and pressure sender three years (40k) ago. Here is a cold start 70° morning facing downhill a bit. This knock (maybe piston slap?) goes away after 15 seconds or so, again, not sure if it is related:

If that noise is cold start only and disappears after a bit, It's piston slap
Very common on the earlier ones

 

[jeremiahm]

The noise from across the driveway goes away, but he noise underneath is persistent.

 

[dkad260]

Is this noise louder at idle when cold or hot?

What happens when you rev it to about 1500 RPM?

I've seen carbon buildup do some weird things, like cant the piston slightly at TDC making a "slap" farther up the bore.

Definitely has a slight hollow sound at one point. With what's been said, check the torque converter bolts.

I have blown a coil doing this on a different vehicle, but maybe disconnect a plug wire and see of it changes. I did this with a motor running and it blew a coil so I would perform this with the motor off...disconnect/reconnect the lead at the coil pack.

Fact it's been like this for 8 months and hasn't gotten worse? A worn rocker will make a lifter tap but that's more distinct.

If you power brake it slightly in gear, does it get louder?

 

[jeremiahm]

Power braking does not reproduce the noise, even up to 3000 RPM.

 

[rdezs]

.... That leads me to think it's more likely under the front timing cover. Wow power braking and under load the timing chain has steady tension. Could be a sloppy timing chain or tensioner is trashed

 

[jeremiahm]

Finally got a good recording of the sound while driving. Phone is mounted in the middle of the dash for this recording. Most obvious between 30-45 MPH. Only occurs under load. This clip is 1500-2500 rpm, no noticeable change in sound. Sound is always there in these conditions, no quiet days. Been doing it for 8 months only becoming a bit louder over that time.

What do the pros think?

 

[dkad260]

Hmm,.can you get a better video around the block at idle for about 20 seconds?

I'm trying to hear about 5hz sound but it doesn't seem like that. Which would indicate a rod bearing. The first video has a hollow aluminum sound so have you verified your torque converter bolts are tight? Also see if you can get a look at the flex plate and look for cracks.

My initial thought is a cracked flex plate.

If you can hold it at 1200 that might make it easier.

 

[rdezs]

If you recall, with a stethoscope the bellhousing was quiet and the noise was pronounced around cylinder number 5. With his oil pressure, I don't think it's a rod or main bearing. Still putting my money on the number five piston pin bushing....

 

[jeremiahm]

Poking around with the stethoscope and the sound seems most prominent from the starter. The ticking sound. It also sounds like the starter is spinning while the motor is running, is this right?