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:
- Check all mating surfaces with a straightedge to make sure they are truly straight.
- If surfaces are straight, place Fel-Pro #1204 intake gaskets on the heads and set the intake manifold in place.
- 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.
- Remove the intake and place a large bead of Permatex Ultra Black silicone sealer on the black mounting surfaces (front and rear).
- 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.
- 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.