Thread: Please help I am racking my brain on this one.

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Good to hear you have things straightened out in your engine! Richard always puts up some really first rate information for us!!!!!!

Any body got suggestions for how to stop the rear of the intake manifold from leaking? Unfortunatley all I get with a gasket set is the two runners for each side of the intake and a tube of black rtv silicone for the front and rear and the rear keeps leaking.

Originally Posted by aahx2011

Any body got suggestions for how to stop the rear of the intake manifold from leaking? Unfortunatley all I get with a gasket set is the two runners for each side of the intake and a tube of black rtv silicone for the front and rear and the rear keeps leaking.

Toss the black rubber pieces over the fence. Glue the intake gaskets to the heads with Indian Head gasket cement.....making certain that you get the gaskets over the bolt holes properly so you won't have difficulty dropping the bolts into place. It is much more important to get the bolt holes lined up than it is to get the ports lined up. Do not worry about port alignment. The science of Fluid Dynamics states that the majority of flow goes right down the middle of the port and that there is little movement of mixture right next to the walls of the vessel (port).
Permatex 20539 Indian Head Gasket Shellac Compound, 2 oz. : Amazon.com : Automotive
Before you lay the beads of Ultra Black on the china walls (front and rear walls of the block that encompass the lifter valley), lay the intake manifold into position carefully and eyeball the gaps front and rear to see how much silicone will be needed to make a seal.
Lay a tall bead of Ultra Black across the top of the rear and front china walls of the block where the black rubber pieces would have gone. Make certain you have enough Black on the walls to seal the intake manifold in the corners at the transition to the intake gaskets. Carefully lower the intake manifold into place, insert bolts and torque to spec. Re-torque tomorrow.
http://www.permatex.com/products-2/p...t-maker-detail
All parts must be oil-free, so decontaminate them with a good solvent. If you use brake cleaner, use it outside only, with the wind at your back. It will wreck your lungs if you breathe it in.

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Originally Posted by aahx2011

Any body got suggestions for how to stop the rear of the intake manifold from leaking? Unfortunatley all I get with a gasket set is the two runners for each side of the intake and a tube of black rtv silicone for the front and rear and the rear keeps leaking.

If I read this right, your laying in a thick bead of silicone at the front & rear of the block. Are you letting the silicone set there for 20 minutes or so before setting the the intake on? I've heard guys say that it works well doing that.

I actually have never had any issue with the rubber seals that used to come with the intake set. I'd apply a thin film of silicone, push the seals down into place and wait a few minutes. Then set the intake down as straight as I could and be good to go. Some guys use some short lengths of all thread as a stud to help guide the intake straight down.

Originally Posted by 34_40

If I read this right, your laying in a thick bead of silicone at the front & rear of the block. Are you letting the silicone set there for 20 minutes or so before setting the the intake on? I've heard guys say that it works well doing that.

I actually have never had any issue with the rubber seals that used to come with the intake set. I'd apply a thin film of silicone, push the seals down into place and wait a few minutes. Then set the intake down as straight as I could and be good to go. Some guys use some short lengths of all thread as a stud to help guide the intake straight down.

If you've never had a problem doing it your way, then continue doing it your way. Different strokes for different folks.
I do not want the silicone to set up (skin over) before I drop the manifold in place. I want it fresh and tacky so it will stick to the china wall and the intake at the same time.

One other thing, you never know how the block, heads and intake have been cut on or altered on the angles, so use a minimum 0.060" thick set of gaskets to take up some of the slack, if there is any slack in the angles. If you don't get the intake/head interface sealed up, the motor can suck oily crankcase vapors into the cylinders. Actually, the head/intake interface is, in my opinion, one of the most important and yet the most overlooked area of building a motor. I read on these forums all the time where a builder is faced with oily spark plugs and generally blames the valve seals because he cannot find an external vacuum leak. But when this is happening on only one or two cylinders, you can pretty well assume that the gasket got wadded up or the matching angles are off from each other due to some machine work in the past, when someone else owned the parts, and you don't have a seal. Lots of heads have been angle-milled and if you're not sharp, you won't catch it.

If a fellow will make certain that the main bearing bores are round and parallel and that all 4 corners of the block decks are equidistant from the main bore centerline, he will have gone a long way toward having the heads sit squarely on the block and therefore having the manifold sit squarely on the heads.

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You're having trouble with the rear seal because you aren't setting the manifold straight down. You're sliding it in, knocking the rear seal out.
Get an extra pair of hands next time, really concentrate on setting it straight down, you'll get a good seal, whether you glue it or use the rubber seals.

I really like Mike's approach of using four pieces of all thread rod (or bolts with the heads lopped off) as guides where you can, like a SBF. That takes all the guess work out of setting it down straight. That one goes into the "neat ideas" memory bank for next time. Thanks Mike!!

the bolts or studs as guides work on engines that have vertical bolts but isn't a cure all for others----angled studs mean you have to lower the manifold from one side and probably is easier to knock the gaskets out-


Something that will work on a chevy is to put your oil primer tool in the dist hole and use it as a guide for the back end-------

The silicone bead at the front and rear of the block as techinspector1 suggests is the best way to seal it and a must do when using an aluminum intake manifold. I have used this method many times without failure, however the silicone can take several days to cure at the thickness required and if you do not let it cure completely it will not seal.

I use a test bead to know when the silicone has cured enough to trim (apply a thick bead onto a piece of wax paper). I clean all of the surfaces with lacquer thinner, mask off the outside of the manifold and block to prevent unwanted excess silicone from sticking to everything (neatness thing), apply a very thick bead of RTV high temperature silicone to the block (rated for oil and coolant), set the manifold gently into place straight down without sliding, snug the bolts and torque to spec.. Wait until the test bead has dried completely (sometimes this takes a couple of days), then trim the outside silicone edges with a razor and remove the masking tape.

The only time this method did not seal for me was when I didn't allow the silicone to completely dry, got in hurry and paid the price of doing it over.

Originally Posted by rspears

I really like Mike's approach of using four pieces of all thread rod (or bolts with the heads lopped off) as guides where you can, like a SBF. That takes all the guess work out of setting it down straight. That one goes into the "neat ideas" memory bank for next time. Thanks Mike!!

Yes, on Ford small blocks it's easier as the bolts are verticle, I cut the head off 4 long bolts and ground a small taper at the cut. Also used a dremel and cut a groove so I could unscrew the "stud" after the manifold was down.

Maybe I'm just old school but using a "lump" of silicone to close off the manifold is just so... "guinea rigged".. I actually prefer the rubberized cork! I can hear some folks groaning over that one but.. to each his own. It works for me!

Originally Posted by 34_40

Yes, on Ford small blocks it's easier as the bolts are verticle, I cut the head off 4 long bolts and ground a small taper at the cut. Also used a dremel and cut a groove so I could unscrew the "stud" after the manifold was down.

Maybe I'm just old school but using a "lump" of silicone to close off the manifold is just so... "guinea rigged".. I actually prefer the rubberized cork! I can hear some folks groaning over that one but.. to each his own. It works for me!

Back before the days of silicone sealers I used to take a sharp center punch and put a staggered line of punch indents along the "china wall" in the back to add just a bit of "grab" to the rubber gasket. Not sure it was the right thing to do, but it didn't seem to hurt anything.... Today I use the thick line of good quality silicone, rigged or not

Originally Posted by 34_40

Maybe I'm just old school but using a "lump" of silicone to close off the manifold is just so... "guinea rigged"..

LOL! The silicone seems to work better on SBC.

Back in the old days we would glue the cork down with the old sticky (guey) black permatex in a tube. It worked most of the time. But to be honest, back then I was a young man and always changing something, seemed like my motors never stayed together long enough to notice any oil leaks! LOL!

Since I have had this leak I have gone through three sets of intake gaskets and each time they did not even come with the rubber china wall gaskets at all. They came with a small tube of black rtv silicone. It is hard for me to use silicone at all, I was always taught that if it has a gasket do not use silicone as that is what the gasket is for. And I have seen what using to much silicone can do to an engine especially when it is used to excess.

Originally Posted by aahx2011

They came with a small tube of black rtv silicone.

Use the Silicone Luke.

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Originally Posted by aahx2011

Since I have had this leak I have gone through three sets of intake gaskets and each time they did not even come with the rubber china wall gaskets at all. They came with a small tube of black rtv silicone. It is hard for me to use silicone at all, I was always taught that if it has a gasket do not use silicone as that is what the gasket is for. And I have seen what using to much silicone can do to an engine especially when it is used to excess.

Being a GM technician for too many years, I have to agree. Use the silicone. Not any silicone, but use the Ultra Black. Of the hundreds of intakes I have done on small blocks, I've only had one come back due to a oil leak. I always put a 1/4 inch bead down for the "China wall". Now are you sure it's the intake? Most blocks have a oil port in the rear along with the dist which can also leak. I have seen a few people forget to plug the oil port or not have the gasket on the dist.

On the few where the "China wall" fell into the block, GM released a Technical Bulliten years ago for how to keep that from happening. Basically you use a punch to create small indents to keep the "China wall" from falling in. I've only used that one time, and I really don't think it was needed. The customer asked for it.