Why my intake leaked

[olddog]

My 5.0 intake was sucking air/oil up out of the lifter gallery. The gaskets were in good shape and look like they could be re-used (not that I would). I have checked the head and intake with a straight edge. I have checked the angle of the seal surfaces. Everything matches up and looks perfect. This has bugged me, as I do not subscribe to the $hit just happens theory of life. If it happens there is a reason.

It dawned on me that an RTV type sealant was used around the water ports, but not the intake ports. So I checked the thickness of the intake gaskets, and sure enough they are about 0.010- 0.015" thinker at the water ports. I suspect the extra thickness held the intake up and left a slight gap at the intake ports. I do not think this is a good practice. I'm fairly certain this was what caused my leak.

[Pete Munroe]

Olddog,

Leaks are ALWAYS a pain and frustration...!

I doubt it was the RTV.

The gaskets, compostion, what ever are pretty solid compared to RTV.

The RTV comes out of the tube pliant...liquid to gel...seems unless the assembler waited for the RTV to pertify, it will squeeze out before the gasket.

I have aluminum heads, iron block.

My intake manifold gaskets failed after 3000 miles...it was I think due to not re-torgueing the intake bolts.

The gaskets...Fel-Pro super something or other...looked like tortured snakes around the ports...but the RTV BEADS at the front, rear, and around the water ports looked to be fine.

Now, how could a semi-liquid-gel-paste RTV could support the manifold higher than the composite gaskets under 22 ft/lbs of torque?

After I replaced the gaskets at 3000 miles, 500 miles later I had a rear manifold oil leak...because I did NOT use ENOUGH RTV to get a solid bead across the rear of the manifold/block interface.

Now, I do re-torque the intake every oil change or so...more often actually...Have 10,000 more miles since the LAST gasket change and no leaks.

Intake gaskets for me have proved to require re-torquing...often.

Pete

[blykins]

Were the end gaskets holding it off the block? I use RTV around the water ports, but just a very, very small application...almost like a layer of paint. It doesn't take much.

[Ron61]

When I had my car with the 418 stroker, I used to get one drop of water hanging off the right front of the block after every drive. I tried everything as it seemed it had to come from the thermostat area, but that was always dry and it was always just one drop. I used rtv and felpro gaskets also. One day I decided to re-torque the intake bolts and a couple of them, including the one in the right front were a little loose. I never had a drop of water after that, but I still do not know where it came from. I just made checking the intake bolts every so often part of my check routine.

Ron

[carmine]

felpros 1250 or 1262 intake gaskets for windsor are regular composit gasket. If you order 1250 S or 1262 S they come with steel reinforsment sandwiched between the composit material. They work great. They might make them for big blocks as well.

[blykins]

Whatever you do, don't use the Felpro Printoseal gaskets. The silicone blows out way too easily and you'll be pulling the intake off again.

[olddog]

Originally Posted by Pete Munroe

The RTV comes out of the tube pliant...liquid to gel...seems unless the assembler waited for the RTV to pertify, it will squeeze out before the gasket.

Pete, I am not an expert or I wouldn't be asking for help on this forrum, so don't take me wrong.

I have worked in the plastic industry for 30 yrs. Molton plastic at the right temp is very similar in viscosity to RTV. We assemble some piping that is 5" ID with a piece of aluminum for a gasket. The seal surface is a 3/4" irous. There are 10 studs that are 1.25" diameter. These studs are torqued to 3000 ft-lb. If we allow a tiny drop of polymer to get on the gasket, it will have a slow leak forever. No matter what you do, you can never squeeze it out.

Where the RTV was on the gasket on both sides, I was measuring 0.010" + thicker than where the RTV was not. I had cleaned the RTV off the other gasket and it measured about 0.005" thinner where the RTV was than the rest of the gasket. So the gasket compressed more where the RTV was. I have no doubt the RTV was holding the intake up at the four corners, and most of the clamping force was going to the RTV areas.

The milled out area where the bolt goes between the ports, was level full with oil. I don't think this area had much clamping force at all.

[olddog]

Originally Posted by blykins

Whatever you do, don't use the Felpro Printoseal gaskets. The silicone blows out way too easily and you'll be pulling the intake off again.

I have the victor rienze (SP?) to put back on.

[olddog]

Originally Posted by blykins

Were the end gaskets holding it off the block? I use RTV around the water ports, but just a very, very small application...almost like a layer of paint. It doesn't take much.

No there were no gaskets on the block. Just RTV.

[olddog]

I just found the second bolt in from the ends, on all four corners, do not turn free. These are the ones where the head has on open spot milled into it. These bolts only turn down three turns freely, then lock up tighter than I can turn with a nut driver. This definately did not allow accurate torque on the end where the RTV was. No doubt this added to the thicknes of the RTV.

I tapped them, but only gain a turn. I'll have to get a bottom tap tomorrow. Since these are heli coiled, are there any special precautions needed?

[Pete Munroe]

Olddog,

I am trying to remember the entire sequence in my total experience of changing out...two...(not a lot experience!)...sets of gaskets on my 289 iron block aluminum head engine.

The Fel-Pro gaskets, I forget the parts number...are the much despised "Print-O-Seal" I think...they have a blue line of silicone? molded around the intake ports and I think the water ports.

The first time I removed the intake, the gaskets were all distorted as if they had been "squirming"...they had not been retorqued in the first 3000? miles.

RTV had made the seals at the front and rear of the block...that was NOT leaking, only the gaskets where they had broken and dropped into the intake ports.

When I replaced the gaskets the first time I didn't use enough RTV at the rear of the manifold and got a oil leak.

The second time I tried to make the RTV bead taller without adding a huge volume of RTV that would glop into the engine...although I am not sure that within reason it never migrates off into the lifter gallery.

But I did use more RTV the next time I replaced the gaskets...mainly as a "tack" strip to make sure the gasket wasn't moved around the intake ports or to insure? a seal at the water ports. as the manifold was lowered onto the heads.

I ALSO used 4 studs to help drop the intake straight down without displacing the gaskets.

The last r&r I did smear a thin film around the water ports and the center section where the manifold heat risers ports were, again mainly to keep things from shifting during assembly.

As the time interval was only about 30 minutes to get the stuff tacky enough to hold the gaskets in place but not yet setup. It seemed the excess merely squeezed out rather than building up a stable surface as nothing was keeping it from being displaced.

When your engine was assembled was the RTV allowed to SET before the manifold was in torqued down?

I have no doubt some plastics can be tough stuff, or maybe even cured RTV, but from what I saw in my TWO examples, seems like the UNCURED rtv will be displaced...

I now retorque the intake often...

Oh, I have TWO bolts that upon retorqueing do not smoothly take up a tightening, but chatter...they are at the front of the manifold, and always seem to need more torque (22 ft/lbs is the max I go) when none of the other bolts will accept an additional application of torque.

Go figure...!

Pete

[olddog]

I did not own the car nor was present when my engine was assembled. The guy I bought it from was very honest and I can tell he didn't take short cuts. He added good quality stuff to the car.

I will tell you that RTV would not work if it all squished out. Every time I have used it, when you take it back apart there is a layer still present.