How to Change Small Block Chevy V8 Intake Manifold Gasketsby Don Bowman
A Chevy small-block intake manifold gasket seals the intake runners and the water ports, and also seals in the oil located in the lifter galleys. A leak in the intake manifold gasket can cause undesirable results such as an oil leak on the front or rear of the engine, a water leak into the cylinders -- which is particularly bad, since water is not compressible -- or a severe vacuum leak resulting in a lean mixture. A lean mixture will cause detonation, loss of power and a hard misfire in the engine. This is a technical process better left to someone with significant mechanical experience.
Place the drain pan under the radiator drain. Open the drain with the pliers and drain the radiator. Close the drain when finished draining. Remove the air cleaner. Loosen the hose clamp with a screwdriver on the upper radiator hose at the thermostat housing and pull the hose off. Loosen the hose clamp on the heater hose attached to the front top of the intake manifold and pull the hose off.
Remove the alternator support bracket where it attaches to the intake manifold, using a socket if this particular engine uses this type of alternator. Disconnect the fuel line, using the appropriate tool. If the engine is carbureted, a screwdriver will do to loosen the clamp. If it is fuel-injected and has a spring lock, use the spring lock tool by placing it around the fuel line and forcing it into the connector and under the spring. While holding the tool in and expanding the spring, pull the lines apart. If they are a snap fitting, lift the plastic clip on the fitting up and pull the lines apart.
Disconnect the throttle linkage from the carburetor or throttle body. Disconnect the TV (throttle valve) cable from the carburetor, if there is one. Loosen the clamp on the vacuum hose to the brake booster located in the back of the manifold or on the rear of the carburetor. You will need a screwdriver or pliers, depending on the type of clamp.
Pull off any PCV valve hose that may be attached to the carburetor or throttle body. Check to see if there is a coolant temperature sensor on the front driver's side of the manifold. If there is, pull the electrical plug off. Check to see if there is a wire to the electric choke and disconnect it if present.
Place a piece of tape directly under the No. 1 cylinder spark plug wire on the distributor cap. Follow the No. 1 cylinder spark plug wire, which is the forward-most spark plug on the driver's side of the engine, back to the distributor.
Follow each spark plug wire on the passenger side of the engine to the distributor and pull it out of the distributor. Remove the distributor cap using a screwdriver. Lay the cap on the driver's side near the brake booster.
Mark the direction the distributor rotor is pointing by placing a mark on the distributor housing directly below the rotor tip. Make a second mark on the distributor shaft and a corresponding mark directly in front of this mark on the intake manifold.
Loosen the distributor hold-down clamp with a wrench and push it back away from the distributor shaft. Disconnect the vacuum advance hose from the distributor, if it has one. Disconnect the transmission modulator vacuum line from the distributor, if there is one.
Disconnect the electrical wire to the distributor. There should be a quick-disconnect near the distributor. If there isn't, disconnect the wire from the negative terminal on the coil. Lift the distributor out of the intake manifold and lay it aside.
Remove all the bolts in the intake manifold with a combination of socket and wrench. Pry the intake manifold up using a screwdriver in the front of the manifold or on the small tabs on the side. Lift the manifold off and lay it on a clean cloth.
Remove the manifold gaskets from the heads. Remove the gaskets that span the front and rear of the lifter galley. Scrape all excess gasket material off the head surface and center span. If the heads are aluminum, be careful not to scratch the heads. Do the same for the bottom of the intake manifold. After all the gasket material is removed, spray the entire mating surface on the heads and intake with brake cleaner and wipe off with a clean cloth. This is to remove all grease and oil.
Place a new intake manifold gasket on one of the heads. Make sure it is on the right side by matching the holes and all the water port openings with those in the head. When you have determined how they are to be installed by matching them to the head, lay them aside so they don't get mixed up.
Spread a thin coat of RTV sealant in a circle around all the ports in both heads. Install the gaskets and make sure they are perfectly aligned over the holes. Install the rubber spanner gaskets in the front and rear of the lifter galley. Most mechanics do not like these factory rubber gaskets because they are prone to leaking. The best seal is laying a ¼-inch bead of RTV silicone from the side of one intake gasket, across the span, keeping it in the middle of the block surface, and ending up on the opposite gasket. Do this in the front and back. The most important part of using this type of sealant is to allow it time to "skin." This means to allow it to dry for approximately five minutes, or until it does not stick to your finger when you touch it lightly.
Pick up the intake manifold and very carefully hold it above the gaskets. Lower it straight down very slowly, making sure every inch of the way that it is perfectly straight, so the gaskets are not disturbed. Lay it down and install the bolts to center it.
Tighten the bolts, starting in the center and working outward. Install the distributor, making sure the round gasket is on the bottom of the shaft. Turn the rotor so it points at the mark you made on the housing. Now turn the rotor about 30 degrees counterclockwise. When the distributor is installed and meshes with the camshaft gear, the rotor will turn clockwise as it meshes. Install the distributor and see if the rotor is located over the mark. If the rotor is off, lift the distributor and turn the rotor a little farther or a little less depending on how far away the rotor is from the mark. Continue until the rotor is right over the mark.
Turn the distributor housing until the matchmarks on the base and intake manifold match. Tighten the distributor hold-down clamp with a wrench. Connect the electrical wire to the distributor, or if it was removed from the negative side of the coil, connect it there. Install the distributor cap and vacuum advance hose.
Plug the spark plug wires into the distributor. The firing order for a small block Chevy is 1-8-4-3-6-5-7-2 and starts with the No. 1 wire which is the one you installed tape under on the cap. Count this firing order clockwise from the number 1 plug. All the even cylinders (2,4,6,8) are on the passenger side and the odd (1,3,5,7) are on the driver's side. This being the case, take the first plug wire closest to the front, which is the No. 2 cylinder and place it clockwise after the No. 1 cylinder. Place the next wire, which is the No. 4 cylinder, which would be the third in rotation or the third spot open clockwise on the cap from the No. 1 cylinder. So the same for the next two wires which, would be the 6 and 8.
Install the remainder of items in reverse order of removal. When you're finished reconnecting the above items, retighten the intake manifold bolts one more time. The gasket compresses and the bolts will come loose. Fill the radiator with a 50/50 mix of antifreeze. Start the vehicle and allow it to come to operating temperature. Check for leaks. Top off the antifreeze as needed. Reinstall the radiator cap.
Things You'll Need
- Drain pan
- 50/50 mix antifreeze
- Common screwdriver
- Set of sockets
- Set of wrenches
- RTV silicone sealant
- Intake manifold gaskets
- Gasket scraper
- Can of brake cleaner
- Spring lock remover for a fuel line with a spring lock connector
Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).