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I'm having a bizarre thing happen. I removed the intake manifold,, did an ls6 valley upgrade, replaced the intake manifold gaskets, and reinstalled the intake manifold. This was about a month ago.
I followed the factory tightening pattern and torque spec of 89 lb inch. I triple checked everything. I got a poor idle and it seemed i had a vacuum leak. checking the bolts,, they had loosened so much especially the middle 6 bolts. The rear 2 bolts didn't loosen at all and the front ones loosened only a small amount. Why did this happen and what can I do? Medium strength loctite says it's good for up to 300 degrees. Not sure it can withstand it. Also, i can't access the last 4 bolts without sliding the manifold out which I really want to avoid.
Are you sure the intake is all the way bolted down right in the first place?
The valley cover bolts interfere with some intakes in some situations. Might want to take the intake off, flip it over, and see if there are witness marks on the bottom of it from those bolt heads.
Are you sure the intake is all the way bolted down right in the first place?
The valley cover bolts interfere with some intakes in some situations. Might want to take the intake off, flip it over, and see if there are witness marks on the bottom of it from those bolt heads.
I was thinking about the same thing. It's the stock intake for the 2001 year (I believe they switched to the ls6 intake this year). It seems to sit flush.
Okay. So luckily I just realized I took some photos of the new ls6 valley cover. I used the bolts that came with the cover. One photo shows a bolt torqued all the way down. I can't believe I took pictures. I rarely do that. I'm going to take pictures of every step of every thing i do in the future. Can come in handy. cleaned the mating surfaces valley cover before being torqued down close up of torqued down bolt.
Does it look like it may cause some small clearance issues?
Beautiful bolts. Look great. Can't tell A DAMN THING about whether they'll interfere with the intake though.
Look at the underside of your intake and see if there are any witness marks from the bolt heads.
I'll take a look. I bought some low profile valley cover bolts. I figured if I'm going through all the hassle all over again I might as well just give it 0 chance of interfering. Now to just make sure I remove the intake without breaking that stupid oil sensor.
Also, I bought some high temperature, medium strength loctite. Would it be a bad idea to apply it to the intake manifold bolts to prevent future loosening?
Last edited by 2001ws6ft; Jul 13, 2021 at 07:17 PM.
I'll take a look. I bought some low profile valley cover bolts. I figured if I'm going through all the hassle all over again I might as well just give it 0 chance of interfering. Now to just make sure I remove the intake without breaking that stupid oil sensor.
Also, I bought some high temperature, medium strength loctite. Would it be a bad idea to apply it to the intake manifold bolts to prevent future loosening?
yes, that's a bad idea. Don't apply loctite to those 89in-lb bolts. It's in the fast intake install procedure to check bolts again after a few miles. They're not exactly the same, but it seems to be the case for the ls6 intake as well.
You should get some buttonhead bolts just to make sure they don't contact the bottom of the LS6 intake.
sounds like the op did get some for the next attempt, there aren't many low profile bolts, so I'm assuming that's what he means. That said, definitely put some anti-seize on the 18ft-lb button head bolts on the valley cover. I've had to remove some button head bolts from the valley cover before, nearly had to cut one off after just 10k miles. They round easy for some reason right there.
But also worth considering: if he needed button head bolts, that would mean he already damaged the ls6 intake with the original bolts. The damage would be done.
sounds like the op did get some for the next attempt, there aren't many low profile bolts, so I'm assuming that's what he means. That said, definitely put some anti-seize on the 18ft-lb button head bolts on the valley cover. I've had to remove some button head bolts from the valley cover before, nearly had to cut one off after just 10k miles. They round easy for some reason right there.
But also worth considering: if he needed button head bolts, that would mean he already damaged the ls6 intake with the original bolts. The damage would be done.
It's possible, but I doubt it. It looks close to flush. If the bolts are in fact interfering, it must be a tiny amount barely flexing the intake manifold. Especially since I never torqued it over 89lbs inch. In any case, I'll inspect the intake since I'll have it off. The buttonhead bolts I ordered recommend 11 ft lbs of torque. I really hate allen drive bolts so I'm going to go with their recommendation over the standard bolt torque spec. I will apply a tiny amount of anti seize as in my personal experience, allen drive bolts round off way too easily. I also6 realized in my photos that the new ls6 valley cover has raised bumps, but they seem to be lower than the bolt heads so I doubt they'd interfere. They look to be as high as the button head bolts would be.
You should get some buttonhead bolts just to make sure they don't contact the bottom of the LS6 intake.
Yup, I bought some. But the more I think about it, the more I doubt it's causing an interference issue. The bolt heads look to be around the same size as the ones that were on the original valley cover.
Hard to imagine that a stock intake manifold would interfere with stock bolts on a stock cover. Always possible, of course. To not check that would be kinda silly. Stranger things have happened.
Lock tite isn't a good idea, for some obvious reasons. But you can use a little dab of high temp silicone. I've used that for years on aluminum intake manifolds with good results. Works well on header bolts, too.
I did this. A little more labor intensive, but it works well.
I don't use button heads very often. Only on non-critical areas where I don't want them to stick up very far. Like fenders. As you said, they can round out pretty easily. I've noticed that factory bolts will round off pretty easily if you're using a 12 point socket. I'm not sure why that is, maybe they're not very precise in size.
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Loosening intake manifold 
