Couple of dumb questions - but I don't see this info in your post:

• Is it a hydraulic flat tappet lifter, mechanical flat tappet lifter, mechanical roller lifter, or hydraulic roller lifter?
• Are the rockers adjustable?

I am assuming it is hydraulic flat tappet and non-adjustable rockers, but worth asking.

Do you have a mechanic's stethoscope? If not get one, they are cheap. Listen along the intake at each intake and exhaust lifter until you identify the noise, then get the rockers off and inspect that rocker/pushrod combo for play. By that I mean get the plugs out and rotate the engine to the top of the base circle on the cam (i.e. pushrod fully down) and look at the movement on the pushrod up and down. Compare it to one that doesn't make the noise.

If the are all more or less the same, you may have a failed lifter. It does happen. Only takes a tiny fleck of metal in the lifter and it won't have the full oil float.

 

 

 

 

Yes...well I am 99% sure that I know where the noise is coming from...the flex-plate.

A mechanic friend of mine advised me that my original rocker shafts might be worn beyond spec. Apparently the rockers can egg shape the shaft over time and get noisy.
So I swapped them out with a new set from JEGS...and almost silence. The engine sounded sooo much smoother but I still had a single tiny tick.
The tick would come and go at different RPMs...really strange.

So I took a mechanics stethoscope and listened all over the top of the engine and I couldn't isolate the noise. The I listened along the block from front to back...and I could hear that the noise got louder as I went back. Just to rule it out I listened to the side of the transmission bell housing (C6) and bingo...loud and clear the noise was coming from inside the bell housing.
I used an old flex-plate on my build...and I think it is the source of the noise. The same friend who advised me to swap out the rockers said that flex plates can get hairline cracks in them and as they "flex" they will make ticking noises that sounds just like a valve. This would also explain why the noise goes away at different RPMs and why I cannot isolate it to a specific cylinder.

So thanks to all for the advice...truck is running great now.

 

So I thought I had the noise tracked down but I am still not sure where it is coming from. I took some slo-mo video of the the problem valves to see if I could locate the problem.
I don't think it is a problem with the cam or the lifters...so the next thing I am going to check is the pushrod length and to see if the valves are sticking on the number 5 or 8 cylinder.
The plugs on all cylinders look perfect and the truck seems to run fine...just ticking like crazy...

Maybe you guys can check out the video and give me some suggestions?
https://photos.app.goo.gl/TY8Hbkg6qJXWhthY8

 

Interesting. Please correct me if I'm wrong, but I hear '2' distinct tapping sounds, both corisponding to function of intake AND exhaust on #6. The sounds are not in sink with others on that bank.

Just a thought here - how do know that the plugs are firing under compression. Just because they bench fire, does not mean they will perform the same under compression. Maybe try sticking a new plug in that hole and see if that helps.

It is a little odd hearing a click on both intake and exhaust.
?????
- Flat lobes on both intake and exhaust?
- Both push rods on intake and exhaust are too short. Sounds strange but who knows. ?
- Both lifters on that cylinder not pumping up. Also strange but again, who knows. ?
- Piston pin loose and making noise both up and down stroke. Strange I know but just a thought. ?
- Perhaps the mouse on that cylinder is not turning the wheel enough to keep up with the rest of the mice. ? Again, just a thought. O WAIT, I'm thinking of a Chebby. It's Monday. A little humor on Monday always makes it go easier.

 

I watched it again a couple times. It looks like its possible that the clicking also happens on one rocker on 5 and one on 7. Is it possible that the cam is loosing it's lobes? Very interesting.

​​​​By the way, like the way you slowed the video down.

 

 

To me, sounds like the intakes on both #5 and #6. Check the valve lash.

 

I found this video last year and just looked it up again. Might try this. Never know.

 

Ok UPDATE! - Most likely bad news but here is what I found after reading all your posts...and I did read them all...thanks everyone for the advice.

Note on the video: Playback online does not sync up the audio and the video correctly. When I watch it on my phone clearly the noise was syncing with the #8 cylinder
Also all my lifter hold pressure really well and do not bleed down.

I marked the valve stems to check for the correct pushrod length...and the #8 cylinder looked abnormal so I swapped in some .030th shorter pushrods on that cylinder.
Noise was still present. I listened across the front of the valves with my stethoscope a and loud and clear the #8 is screaming! It is actually discolored from so much heat build up. I only ran the engine for a minute and it was way too hot to touch and all other valves were only warm to the touch.

Exhaust valve war pattern looks like the rocker is chattering over the surface...not good

Exhaust valve is discolored from heat...it would burn your skin to touch it...all others were just warm to the touch

note the shards of black plastic or ceramic sitting on the #8 intake runner...i have no idea what that is...its not magnetic

So it looks like my #8 exhaust valve has a ton of excess friction, but still moves...Now what do I do?
Is this an oiling problem, or a valve guide problem in your opinions?

Thanks again.

 

The coloring looks like that valve has gotten pretty hot. Do you have a valve spring compressor? If were mine, I would pull the spring on that valve and see if the valve moves up and down freely and check for guide ware wiggling the stem around. That's a whole lot of ware on that valve stem end. While you have the valve assembly off, take the pressure off that rocker (pull the spring back) and wiggle the rocker checking for ware and than slide the rocker away from where it sets on the rocker shaft and look for ware in the shaft.

 

Looks like you've got a bad valve guide, the discoloration and heat is from exhaust gasses coming up between the valve and the guide
I increased the size of your photo and can see the valve stem under the retainer appears to be black possibly from exhaust carbon
Also that spring has a very thick shim under it, do any of the other springs have shims under them.
Do to the needed clearance to prevent coil bind on higher lift cams one hardly ever see's thick shims like that used with aftermarket springs.

One thing you never told me was if the machine shop installed the matching spring set for that cam or if they reused your stock springs.
The black stuff your seeing could be parts of the valve seal

 

x2 valve guide.