Mailbag: Achieving Proper Cylinder Head-to-Manifold Seal in 6 Easy Steps

You’ve got questions. We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re exploring a technique for proper intake manifold-to-cylinder head sealing.

C.M. Chicago, IL

Q: I purchased a set of Edelbrock aluminum heads for my 1979 Corvette 350 engine. The engine has a 280-degree duration solid lifter camshaft, 10:1 compression pistons, and an Edelbrock Performer RPM intake manifold.

The problem I am having is that I can’t stop oil from leaking into the intake runners. My vacuum is low, too (8-10 pounds). I contacted Edelbrock and was advised to return the heads to them. They checked the heads for sealing and leakage, but could not find anything wrong with them. Since I put the heads back on the engine, I changed the intake gaskets three times and intake once. The problem is still there.

I had no problem with the old cast iron heads. I took the engine to a local engine builder, and he said the block was not cut or decked, just bored .030 over. I would appreciate any help you could provide.

A: Misalignment is a very frustrating problem, especially with lightweight aluminum heads and intakes. Here is a procedure you may want to try to get those parts to seal up:

1. Check all mating surfaces with a straightedge to make sure they are truly straight.
2. If surfaces are straight, place Fel-Pro #1204 intake gaskets on the heads and set the intake manifold in place.
3. Check for any mating surface gaps with a .003-.005-inch feeler gauge. If there is a gap on the lifter valley side of the intake, then the mating angles are off and the intake needs to be corrected. If no gaps are found, make a visual note of the block-to-manifold gap width.
4. Remove the intake and place a large bead of Permatex Ultra Black silicone sealer on the black mounting surfaces (front and rear).
5. Lower the intake back on the engine. Following the manufacturer’s recommended torque sequence, torque the intake to 30 ft.-lbs. in 10 ft.-lbs. increments.
6. Let the intake sit six to eight hours to let the silicone set. After several days of use, check the bolts to make sure they are still at 30 ft.-lbs.