Recently di d a ls6 cam swap and put everything back together and this noise developed one day after running the truck hard on the highway. I sometimes get up past 6500 so I wouldn't be surprised if it is a lifter or pushrod.
I added some marvel mystery oil to help loosen a possible stuck lifter but jow it sounds like a mechanical noise every few seconds.....like something is bouncing around? Anyone have any ideas? The sound is right at the end of the clip.

 

 

Sounds like a collapsed lifter...not sure if the other clunk sound is related but it's definitely a possibility.

What's the rest of your valvetrain like? Stock pushrods? Stock rockers? Stock springs?

 

I am still running stock pushrods for now. Havent decided if I should get them cryo treated or get hardened ones. I have ls6 valve springs and stock rockers. With the cam being smaller I had the heads decked to match them. .025 I think it was. Ls2 timing set and new oil pump were thrown in fr good measure if that matters.

 

If the heads are milled .025 you might need 7.375 pushrods. I would get a push rod length checker. Pre-load might have been a little much could have led to this. Could be a lifter

Maybe a rocker arm bolt backed out and the rocker is loose!

 

Pushrod Tap Video by milkey57 | Photobucket

Had a similar situation, it was a loose rocker.

 

I checked the preload and pushrod length using a guide from ls1 tech. Count turns past 0 lash to determine pushrod length. Shouldnt be a problem as I tookvas much off the heads as the base circle difference by sqapping cams. I have checked and recheked lash. Nothing is lose but I definately hear stuff. I'm thinking I might just have to bite the bullet and pull heads and timing cover to find the problem. Unless anyone has any ideas.

 

Did you set #1 cylinder to tdc and tq all rocker bolts to 22-25ftlbs? They don't individually get adjusted like older small blocks. I'm sure you know this just trying to help you trouble shoot!

If the rockers and pushrods are all good then the only things left I can think of is oil pressure which you put a new pump in or lifters. What is your oil pressure at idle?

Does the sound only happen at idle or when you rev it it continues?

I help a friend do a cam swap a couple of months ago and we soaked the ls7 lifters over night in oil, but it made loud taping noise for the first 5 min until to lifters filled up with oil. Now he has never had another sound.

 

I followed the prrocedures in the chiltons for setting lash. My oil pressure is good it sits pretty high....high 40s I think...I have to watch one of my videos to be certain.
The sound happens at wierd times. Its like an intermittent clanking noise. It doesn't change with rpm.
I soaked mine as well not overnight but a few hours worth and the motor was sounding good until this noise popped up.

 

There's really no "lash" adjustment in these motors. You just set the pedestals in, set the rockers on, and torque them down. How did the lash adjustment procedure work?