I have a Chevelle with a LSA/6L80E that I just got running. On the first start it had this clattering noise that people said sounds like the flexplate. I ruled out any of the accessories driven by the belts up front by removing the belts and the noise kept happening. I unbolted the torque converter and slide it back and the noise continued. I inspected the flexplate as good as I could and didn't see any cracks but to me it sounds like this is the issue. I blued the flexplate to see if it was rubbing anywhere and it wasn't, clears the starter without issues. Kind of at a loss to what this noise it and looking for some help if anyone has some advice where to go from here before I drop the trans or pull the motor. I have a few videos posted on YouTube of the noise. Here is link from today and also posted in the comment below.
https://youtube.com/shorts/CBWX1YIBU2s?si=pR-ILvwHMBiVZJvv

I have good oil pressure, rockers are all set and torqued, headers clear frame and nothing rattling.

 

 

I think thats a rod knock IMO

 

That's piston slap
Just about every 6.2 ever has that noise on cold start. Especially anything with enough abuse or miles to wear past the factory skirt coating.
You will likely disassemble the engine, notice nothing catastrophic, reassemble and have the same noise

The 6.2 have a large bore with a short skirt and very little wrist pin offset. The result is a piston that will rock at the top of the bore and has "piston slap"
There are factory ignition tables even titled "piston slap" in an attempt to reduce the noise, but alas you'll never fully get rid of it

 

Did you watch the video all the way till the end? It gets much worse to where I shut the car down. I have a ls3 in my truck and this sounds horrible compared to it like something is about to break. I have a few more videos on my youtube channel and most of them start/idle decent for 15 seconds then develop a loud rattle noise. I ordered a new flexplate hoping I will find a Crack in it although I don't see anything through the inspection hole or starter area. To check if it's piston slap, should I let it idle till it's up to operating temp and see if the noise goes away? Running thicker oil would help I'm guessing. Definitely stumped at trying to diagnose this issue without starting to pull everything apart.

 

I figured it was the microphone filtering
If it really does get that loud towards the end
It's rhythmic almost like a lifter/pushrod/rocker. Pull a valve cover and watch while it runs. Shouldn't make TOO much of a mess. Or at least watch while cranking
I strongly doubt this is a flexplate issue

 

Thanks for the help. I started it up this time and let it idle to operating temp and it sounds normal now. This is the first time in months it has ran like this and I haven't done anything but let it warm up past 30 seconds or so before shutting it down. Ran good for a few minutes, shut it off and turned it back on and the rattle started back up. Sounds louder when I am under the car. Hitting the gas petal increases the clattering, faster and louder.

 

 

 

Sounds like a CRACKED Piston to me...

But I won't rely on a Recording to asses the Sound.
The Sound may be totally different in person (Tone, Pitch, Reverb, Etc).

 

My game plan it to move the transmission back and take the flywheel off in hopes that it is cracked then install a new one. If that wasn't the issue I am going to pull the motor apart.

 

Today I took the valve covers off to inspect while running. Car wouldn't start but would turn over enough to see that the intake rocker on #7 cylinder wanst getting oil. I pulled the spark plug and put a bore scope inside to find this damage to the top of the piston.

 

Piston tops 3 and 7 look pretty beat up. Cylinder walls look good woth no damage.

#7 head damage

#3 head damage

Piston top #7

Piston top #3

#5 piston top

#5 head

 

So, what was in it?

 

It must have chewed it up and spit it out already cause I was unable to find anything in the combustion chamber or stuck in the head. I still haven't pulled the passenger head yet but I'm assuming it looks similar and hope to something inside that I still asking the rattling sound.

 

I put a bore scope down the passenger side and all bores and piston tops look good with no damage.

 

Hate to see this. But, at least you found your problem.

 

I agree. I guess it's time to do forged internals while the motors out.

 

BTW, looks like a clean install too. Good luck, keep us updated

 

Thanks man. It should be a badass protouring car once it's finished up.