Were you using the matching cam caps for the head? You can't mix and match them. Even something as simple as putting the cam cap on the wrong direction (they have an arrow on them that points towards the front of the motor) can cause issues. The cams should be able to be turned by hand once assembled and the cam gear is on. If not, there's and issue and it needs isolated and addressed. During this rebuild I caught my mistake on one cam cap that I accidentally installed backwards. I rotated the cam like I always do to make sure it was free and it just seemed a bit harder to turn than the other cam. I loosened all of the bolts and retightened them, and it didn't fix it. Took it all apart and inspected the cam and journals, and they all seemed fine. I then started putting the cam caps back on without the cam in so I could measure clearances when I caught my mistake of the cam cap being on backwards. Spun it around the right way, re-installed the cam, and it turned nice and smooth again.
If they turn smoothly during install, but you're getting damage later, it's an oil supply issue. Oil pressure values need confirmed IMMEDIATELY upon startup. noisey lifters are a sure sign of low oil pressure. Don't just let it go. Noisy lifter are the engine's way of telling you there's something wrong. Most engine builders want to run really loose oil clearances. Don't let them. Follow the FSM for bearing clearances. If the main and rod bearing clearances are too big, the head will have low oil pressure and you get noisey lifters, or worse, damage like you've experienced. If the oil pressure is good, but you still have noisey lifters, you have an oil supply issue to the head. There's a check valve in the block to prevent oil from draining out of the head when it's off. Without it, the lifters would be noisy and have to pump back up every time you started the car. The issue with the check valve is that it's easily plugged up by ANYTHING. It has very small internal passages. If it gets plugged even a little, the head starves for oil. The issue with check valve is removing it undamaged. It may be possible to do, but I haven't found a way. I've ruined it every time I've removed one. Replacements aren't available either. Fortunately the check valve from an early model VG30DETT will work. PART NUMBER 11036-1P600,
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