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I installed new intake manifold gaskets 6 months ago and now they've slipped/shifted out of place. Both sides have shifted, leaking vacuum, creating a rough idle.
They were fine to start with, no leaks and good vacuum. I was extra careful installing them, using guide bolts to lower the manifold and Gasgacinch on the gasket to hold it in place, and proper torque sequence.
The reason I took extra care was because the exact same thing happened 6 months before! So this is twice. First time with Edelbrock gaskets, this time with Felpro.
The manifold I've had for many years on the previous motor. No problems. This motor is a '96 I got from a donor truck.
I figure something must be warped....head or manifold.
Has anybody seen this before?
Any suggestions or ideas?
IDK, a decked block issue would tend to make the manifold sit high not low.
Did you use the end rail gaskets?
Did you block the crossover?
Truly odd, best guess would be a manifold fitment issue. That as the manifold is expanding and shrinking as it heat cycles the gasket is walking out.
FWIW when I install intake manifolds I employ a separate glue and seal process. My first step after prep and everything of course is to use a sealer that is also a very good glue. Permatex #2 is a good choice. I use this to glue the gasket to the manifold. I'll place the gasket, let it set a bit then set the manifold in place on the heads with a weight on the carb surface. After this glue/sealer has setup I then install the manifold with a bit of standard RTV silicone around the water ports and with a gasket making RTV like The Right Stuff replacing the end gaskets.
Wow. I pulled off the manifold and the gaskets are pulled and distorted all over the place, with multiple vacuum leaks above and below the manifold.
You can really see how much the gasket has moved where it has pushed into the hold-down bolts.
I used RTV on the end rails when I installed it. All good no leaks there.
I used the exhaust crossover block pieces that came with the Felpro gasket set.
I don't know the history of the engine but I don't see any signs that it's been opened up.
I ran out of time to fully check out the mating surfaces, plus I don't have a proper straightedge to check with anyway. But it does look like the head surfaces might not be straight. Uggh. I don't know what could have caused this in the first place, or how it's possible. (if it is actually the case)
How completely bizarre, it's like everything was pushed out with the exhaust crossover as the center. That last pic where the gasket has pushed over the bolt is very telling, that's some force not just a loose gasket shifting. I'll have to think about this.
Make sure you use a torque wrench on the intake bolts or be very careful and don't overtighten them. I am not sure what your problem is now, but I do know the way the Ford bolts are designed straight up vertical like they are, if they are overtightened they can pull the head up a little bit and cause head gasket problems.
I would clean everything up and put the intake back on the engine with no gaskets, and see how it sits on there and maybe run a feeler guage around in the crack between the intake and the head and see what it's like. Also see what the ends of the intake look like. If the heads have been shaved some, that will move the bolt holes down, and the intake won't match up correctly. It can bottom out on the ends before it can squish the gaskets on the sides. If the amount of feeler guage you can squeeze into the crack is about the same as the thickness of the side gaskets, then you are not getting enough squish on the gasket to hold it tight.
If that's the case, the intake can be milled off to correct it.
All of the surfaces are straight, as far as I can tell, using a straightedge.
When I installed the manifold I followed the tightening sequence in the manual, and torqued in several stages with a torque wrench. (about 25 ft/lbs IIRC)
However, I did discover a crack on the underside of the manifold.
I got some brake cleaner to go through the crack to the other side. It mostly affects the exhaust crossover (which is not in use) But it does also affect the intake runner right next to it. It's the only intake passage with a black coating on the inside, just near the exit.
I'm thinking that maybe when the manifold is torqued down, the crack opens up a bit and full clamping force is not applied to the gasket.
I still don't understand how that crack could cause so much gasket movement....but that's all I have to go on right now.
If there is a problem and the end gasket surfaces are hitting before the side gasket surfaces, then when you tightened the bolts it could have cracked the intake.
By the way, I would not run those exhaust passages blocked, but that is my opinion on that. I have run the restrictors, but when I blocked them totally the engine became very cold natured. That's a whole different discussion but you need to make a decision now while messing with it.
If you get another intake, or have that one welded, you need to check the fit or it can possibly happen again.
That intake has been machined. The tree ring looking grooves that are most visible in the 3rd picture are from a decking mill. Best guess from the milling and the crack is that the milling was done poorly. That the angle is off, particular that if laid on the head there will be a gap on the underside of the mating surface. The reason I say that is that it would cause the crack. That the angle between the two surfaces that should be 90deg is more then 90.
This manifold came with the engine that it was on before?
The end seals don't bottom out when the manifold is installed. The cured RTV is at least 1/16" thick.
Btw, I don't run the exhaust crossover because I'm on propane fuel, it's not needed.
The intake is an Edelbrock Performer that I bought over 20 yrs ago...but I have a factory Ford cast-iron 4bbl manifold sitting here, I might just bolt that thing on.
Hey BruteFord, I noticed the milling marks on the manifold surface and thought that must be from Edelbrock, but now that you say it, I did have an engine with this manifold rebuilt at an engine shop years ago. Those marks, and the misalignment could be from that. Hmmmm
Hey BruteFord, I noticed the milling marks on the manifold surface and thought that must be from Edelbrock, but now that you say it, I did have an engine with this manifold rebuilt at an engine shop years ago. Those marks, and the misalignment could be from that. Hmmmm
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