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post #1 of 33 (permalink) Old 05-12-2017, 10:00 PM Thread Starter
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LT1 intake won't seal

So I've had heads milled .0010 of an inch, new valve guides, seals, valve job...... blah blah. All the necessary from having a blown head gasket. However, I didn't read that you should also have the head milled to match the heads?? Is this that important? I assembled everything and used the copper sealant in the front and rear of the intake, and the entire passenger side leaked. I sprayed parts cleaner along the entire intake to determine this. Driver side was fine. I only used felpro gaskets and copper sealant the first time. Then this evening, I purchased new intake gaskets(felpro) and some gray RTV silicone. It was very soft or runny in my opinion. I put a thin layer on the heads, and on the intake. Placed the intake gaskets in between( like a sandwich). And now it only leaks between cylinders 2 & 4. ? WTF????? I'm so pissed right now. What would you guys recommend I do. And I torqued the intake bolts according to Chilton specs, which I believe was 35ft/lbs.
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post #2 of 33 (permalink) Old 05-13-2017, 07:04 AM
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The intake on a lt1 engine needs silicon sealer at front & back.Surface where intake meets heads, on all 3 pieces should have been checked for flatness and surfaced if needed. Sounds like it's needed.
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post #3 of 33 (permalink) Old 05-13-2017, 07:53 AM
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Lay your intake on the heads/block with it dry (no gaskets) and see if the mating surfaces are parallel where it meets the heads.
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post #4 of 33 (permalink) Old 05-13-2017, 09:52 AM Thread Starter
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I did lay a THICK BEAD of the high dollar copper gasket sealer. It wasn't leaking from the front or back. Only on the passenger side of intake. Initial install was the entire length of the passenger side. last night, I pulled it off, installed new gaskets again, and used a thin coating of permatex gray on heads and intake, to sandwich the gaskets in. And now it only leaks between cylinder 2 &4.

Shoebox: by laying intake in there dry? With valve covers and such installed, will I be able to see some type of gap?

I've never done LT1 engine work till this car. All my old 350sb engines never leaked at intake. And I never read you should mill intake at same time as heads, until I picked my heads up and was researching the install instructions. I cringe at the thought of 2-3 more week wait for my intake to be milled now? Gotta be something I can do. I put a straight edge on that side, and can't see any variances on the surface.
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post #5 of 33 (permalink) Old 05-13-2017, 11:07 AM
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you should not need RTV on the heads....just the front & rear china wall of the block. I use Permetex black "ultra". about a 3/8" thick bead on china walls running up about 1/2' onto the heads on each side of china walls. wipe all mating surfaces with acetone and make sure the surfaces are perfectly clean before install

I use the FelPro "printo" seal intake gasket

do as shoebox suggests and lay intake in position without any gaskets or rtv to confirm all areas sit flush

I have seen intake manifolds that need the holes opened up some when heads AND block have been decked more than they should to get the intake manifold to sit flush
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post #6 of 33 (permalink) Old 05-13-2017, 11:13 AM Thread Starter
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I didn't have any block work done. Just the heads. And only .0010 of an inch. So not a lot. So sounds like I may need to have the intake milled flat? Correct?
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post #7 of 33 (permalink) Old 05-13-2017, 01:26 PM
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Quote:
Originally Posted by Adrien95Lt1 View Post

Shoebox: by laying intake in there dry? With valve covers and such installed, will I be able to see some type of gap?
Valve covers won't matter. What you want to view is the relationship between the intake and the head surface.
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post #8 of 33 (permalink) Old 05-13-2017, 01:56 PM
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Quote:
Originally Posted by Adrien95Lt1 View Post
I didn't have any block work done. Just the heads. And only .0010 of an inch. So not a lot. So sounds like I may need to have the intake milled flat? Correct?
0.010... 10 thou not 0.001 which is 1 thou more likely.
10 thou should be ok without milling the intake.
I had my block decked by about 0.030 thirty thou and had issues with Edelbrock LT4 manifold being crap.
I ended up buying my own milling machine to true it up.

I would clean everything up and dry fit the manifold.
Check that bolts fit easily and/or drill/file the bolt holes a little bigger towards the bottom edge. The bolt holes in the heads are now lower than before.
Also you can measure the gap on front and back of the block. I can't remember exact figure but anything around 0.020 to 0.040 would be fine just to make sure the manifold is sat on the heads not the block.

Mitch
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post #9 of 33 (permalink) Old 05-13-2017, 03:42 PM
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Quote:
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I didn't have any block work done. Just the heads. And only .0010 of an inch. So not a lot. So sounds like I may need to have the intake milled flat? Correct?
....only if the intake manifold is not flat...hold a good straight edge across the intake ports and look to see if there is any clearance issue, especially for the ports involving the cyl you felt leaked

what more likely is going on is because of the head decking they now sit lower so as noted you "may" need to elongate the bolt holes in the intake manifold

by placing the intake manifold on dry (without gaskets or rtv) you should be able to see if it does not sit flush against the heads

Did you use the small plastic holding tabs on the intake gaskets making sure any broken off tip from old gasket is not recessed in the hole they go in?

did you use the fel pro "printle" gaskets? (they have the blue sealant stripe around each port)

Did you install a thinner (.029) head gasket when you put the heads back on?
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post #10 of 33 (permalink) Old 05-15-2017, 06:18 PM Thread Starter
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Quote:
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Quote:
Originally Posted by Adrien95Lt1 View Post
I didn't have any block work done. Just the heads. And only .0010 of an inch. So not a lot. So sounds like I may need to have the intake milled flat? Correct?
....only if the intake manifold is not flat...hold a good straight edge across the intake ports and look to see if there is any clearance issue, especially for the ports involving the cyl you felt leaked

what more likely is going on is because of the head decking they now sit lower so as noted you "may" need to elongate the bolt holes in the intake manifold

by placing the intake manifold on dry (without gaskets or rtv) you should be able to see if it does not sit flush against the heads

Did you use the small plastic holding tabs on the intake gaskets making sure any broken off tip from old gasket is not recessed in the hole they go in?

did you use the fel pro "printle" gaskets? (they have the blue sealant stripe around each port)

Did you install a thinner (.029) head gasket when you put the heads back on?
I used felpro regular old head gaskets, no blue sealant. Used what I believe are standard thickness head gaskets. I will post pics of what I seen. How do I "elongate" the bolt holes in the intake manifold? One side seems to have a bigger gap than the other one.
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post #11 of 33 (permalink) Old 05-15-2017, 06:21 PM Thread Starter
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Wont let me post the pics. . It's a solid 1/16" gap everywhere. Some spots only 1/32. And it seems to be closer to an 1/8" on driver side front. The intake sits flat on the front and rear of block, leaving gaps along the edges of the intake.
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post #12 of 33 (permalink) Old 05-15-2017, 09:42 PM
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if manifold sits just on front & rear china wall leaving 1/16"-1/8" gap along heads.....than those heads got seriously decked.

the head gaskets, whatever ones you used, would not have the blue "sealant" I noted.

The intake manifold gaskets if they are the FelPro "printle" line. Those have a blue sealant bead around each intake port. They seal better than "stock" type. But if you have the kind of gap you note, no gasket will seal that.

Elongating the holes in intake manifold won't work if the manifold will not even sit flush. If it did and the holes on manifold didn't line up with the holes on the heads than yes elongating them would work.
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post #13 of 33 (permalink) Old 05-16-2017, 06:28 AM Thread Starter
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So what the heck can I do? 2 intake gaskets? And black RTV around intake ports to help seal?
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post #14 of 33 (permalink) Old 05-16-2017, 04:27 PM
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Originally Posted by Adrien95Lt1 View Post
So what the heck can I do? 2 intake gaskets? And black RTV around intake ports to help seal?
no...without pics I understand your issue is sitting flat on motor with no gaskets there is a gap between manifold and heads on both sides of the motor, right?

this after you had heads done......just sounds like that shop decked quite a bit off the heads making them sit lower than they used to be enough to introduce this gap.

Not been in this situation before and I have had a few sets of used, re-done, heads on motors

no doubling up on gaskets or rtv is going to resolve this

"if" the issue was the manifold sits flush all around but the holes in intake are slightly high to line up with the threaded hole on heads then you elongate the holes on the intake manifold to get the bolts through. But apparently this is not your issue

maybe someone else can suggest something...pics of your issue would help
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post #15 of 33 (permalink) Old 05-16-2017, 06:15 PM Thread Starter
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All my pics exceed the file size quota by about 70kb. I keep trying. Dropped off intake today, and it's definitely warped. He checked it while I was there. But was surprised to hear the situation? He swears they only cleaned it up by .010.
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