An intake manifold connects the cylinder head to the carburetor or fuel-injection system with long tunnels. It must bind correctly with the cylinder head or the fuel/air mixture will leak out and affect performance or present a safety hazard. Engine designers use bolts to do the joining and provide strict instructions for the proper installation.
The intake manifold doesn't bind directly with the carburetor or fuel injector and cylinder head. Metal parts change shape under stress. To provide a good seal, engine designers use gaskets made of a softer material to conform to both pieces of metal being joined. Bolts keep the assembly together. The joint between the intake manifold, the carburetor or fuel injector, and the cylinder head must be evenly and strongly constructed or the gasket will fail.
Before proceeding any further, the mechanic should study the intake manufacturer's instructions and specifications. All surfaces have to be cleaned of old gasket material, grease and dirt. The bolt holes have to be cleaned of metal, grease and thread-locking or any other compounds. The mechanic needs to spread sealing compound on the gasket according to manufacturers instructions and position the gasket on the cylinder head. He can use a small dab of sealing compound to keep it in place. Installation is much easier using guide studs. The mechanic cuts the heads off two bolts of the same size and screws them into the bolt holes just enough for them to hold. The mechanic can simply hang the intake manifold on the temporary studs while he screws in the permanent bolts.
The mechanic drops the intake manifold onto the cylinder head carefully, taking care not to damage the gasket. He makes all of the bolts finger tight before proceeding. The bolts should be tightened according to the manufacturer's recommendations, usually starting with the inner most bolts and alternating sides as the mechanic works outwards. The tightening is done is stages; finger tight then an intermediate torque and the final torque. On the other end of the intake manifold, the bolts connecting the carburetor to the intake manifold must be tightened in a criss-cross pattern to the manufacturer's specification. The mechanic must take care not to the damage the gasket.
