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What would cause a Intake Manifold to....

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1.4K views 18 replies 7 participants last post by  Gibson17  
#1 · (Edited by Moderator)
What would cause an intake manifild to repeatedly leak after instals from the rear besides improper installation?

Ive installed the intake on my 302 based engine 4times in the last 2 yrs (1 intake swap) and it repeatedly leaks from the rear... I replaced the motor 2 yrs ago with a 347, and ever since ive had this problem... I never had this problem on my previous engine with head and intake swaps. The heads i have are aluminum gt40x's and ive had them milled a little when i lost a washer down the runner on my previous engine...Thus the new motor. Ive tried it all, Silicone, cork, cork and silicone and the preformed end caps with no success. I also used guidance studs on installation every time! Could it be buildup in the crancase? What would cause that? The motor is supercharged so keep that in mind. would putting the crankcase under vacume be the solution? I'm STUMPED.

Edited: When looking to buy parts of any kind use the Classifieds Forums. Do not ask for parts for sale or wanted in tech threads. No exceptions.

Keith
90 Saleen 347sc
 
#4 ·
if you are running high boost without an evac set up, that could cause it, but you may want to try a double gasket or something. As far as the heads being milled, I wouldnt see how that would cause the intake/block to not seal. Not really sure, any pits or anything on the intake?
 
#6 ·
no the intake is fine, thats why i did a swap, just in case the lower i had on there wasnt kosher. I went from a saleen/vortech to a gt40. yeah i know i probably gave up some hp there... but i just wanted be sure it wasnt my saleen intake. well now i know its not as my gt40 is now leaking... although it did hold for a bit longer than the last few times.

Also, when your taking high boost, how high are we talkin here? could a bad pcv and screen be the culprit?

Both intakes are aluminum.
 
C
#7 ·
I had this same problem on my non supercharged 347 for a while. I was beginning to think I had excess blowby on my new 347. I probably changed gaskets 5 or 6 times in 2 years. Last time I did it, I was just really carefull to make my sillicon beads nice and thick. I let it dry for just a few minutes, maybe 5 or 6, then carefully layed the intake using a couple of dowels to guide it in. I think it has been about 7 or 8 months and the car runs great, and i check the back of the intake all the time because I am afraid its leaking again. Its been dry ever since. I bet your car runs like crap when the leak gets bad enough,huh? I know mine always did. I think I just needed to put it in perfectly. I don't ever want to have to break that seal now,lol.
 
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#8 ·
did you just use a bead all the way accross? because i tried that, i also used the prformed end caps last time and even they didnt work with silicone... how thick of a bead should i use? also what type of form a gasket did you use? Ultra black?

ANY OTHER IDEAS??

keep em comming i appreciate the response.

Keith
 
8
#9 ·
mine has never leaked and this is what i do:
make sure everything is super clean then lay a 1/4" bead of rtv silicone (grey)
i then lay the preformed gaskets down and make sure they stick alright (felpro)...lastly, i use a helper to hold the fuel rails out of the way while i drop the lower in as straight as possible making sure the gaskets don't shift...i think it's possible the mating surfaces aren't very true in your case..i would have a machinist check both manifolds and even the block if there is any suspicion...funny part is i use GM assembly adhesive since my dad work's for them...
 
J
#10 ·
the bead has to be thick enough that the intake really sits into it and makes a good contact. I have to say that the cork gaskets are pretty much worthless, I always use silicone and never have any problems with it. Also make sure you clean the intake and block surface and run the bead up to the point where the water jaket is on the head, this will help get a good seal. After you do the install make sure you give it plenty of time to cure. As far as the evac kit if its a passive kit that will be fine and help reduce crank case pressure. I don't have a super charger or any forced induction "see my sig" and when we would spin it past 6000 on the way to 8000 it would really blow oil right out the breathers on the valve covers "even with baffles in them" until we installed the evac kit. And please don't try to run a vacume pump "racing style active pump" on thing if it is a street car, had a freind did it against what he was told by a NHRA pro stock freind of ours. Needles to say the pump worked great just like it was supposed to and it was cool to see a 1000hp car on the street but the mist oil that the motor depeded on at low RPM's was absent due to the vacume pump and negative crank case pressure (this is what the engin builder told us) and he ended up spinning a main and taking out two rods and the crank within a week. I sure you know crower rods and a bryant crank are not cheap, he learned the hard way so I guess we don't have to.

hope this helps good luck
 
#11 ·
Ok, the evac kit interests me. Everything you guys have reccommended to this point i have done, im pretty sure evryuthing is true, as the heads were decked and the block is reletively new... BUT... i guess i will be changing it again for the 5th time!!! AHHH, might as well go bavck to the original saleen intake... On the back deck of all of your engines i assume there is abosolutley no oil, not even a residue? at first mine was wet, right now its starting to get a residue and smokes on occasion, i assume from dripping onto my LT's like before when i noticed it was leaking, but now if i jam on the car a little.... not too bad to about 4500-5000 it looks like a james bond smoke trail behind me.... people are like sweet car until that happens!!! F'in saleen!! lol. I think an evac kit may be the way to go. how much did you pay for yours and where did you get it?

Keith
 
#13 ·
I don't know for sure, but decking the heads without milling the angles on the intake may be causing fitment problems. Actually, I'm pretty sure that is the problem. I saw a chart somewhere, (it's on the internet, search away) that explained how the intake would have to be milled for a corresponding milling of the heads.

What you've done by milling the heads is essentially made the gap for the lower intake to sit in become narrower. It's sitting higher and probably not sealing worth a flip in more than just the rear. I guess the severity of the mismatch would lie in how much you've milled the heads. If I were the Shell answer man, I'd give you the numbers you need to get your intake milled to, but I'm not, sorry.
 
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#14 ·
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#15 ·
lol shell answer man!!! that was o.k. thanks for the laugh!

When the heads were milled, it was done so little that it shouldnt make a difference, it was a local machine shop that checked out the heads to make sure they were ok, mainly the valves on cylender#1... so i hope that aint the problem, but it may be.... my brother is a machinist so i guess ill have to send him the parts to have them checked... thanks, i think your confirming my worst suspicions... anybody else agree with noslow?
 
#16 ·
i also recently broke my belt on my sc so ive been driving it for like a week now without the charger spinning.... could that have any ramifacations? i know its alot of piping for the engine to breath through going through the intercooler an all.

Keith
 
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