The head gasket on a small block Chevrolet 350 engine forms the seal between the engine head and cylinder block. This gasket must seal the combustion areas of the head and cylinders, as well as the coolant and oil passages. The combustion areas are under extreme stress, with engine compression and the combustion process. When the gasket blows, it can allow combustion or compression to enter the cooling system, forcing coolant from the engine. It may also cause coolant to leak inside or outside of the engine. A blown head gasket is a serious issue; it can take 12 to 20 hours to replace both head gaskets in a Chevrolet 350 engine.
Disconnect the negative battery terminal. Place a drain pan under the radiator, and open the drain petcock at the bottom of the radiator. Mark the distributor position on the intake manifold, and remove the distributor. Disconnect all the wiring to any connectors on the intake manifold, after noting their locations. Disconnect the upper radiator hose from the engine. Remove all the fasteners from the intake manifold. Lift the manifold straight off the engine.
Disconnect the exhaust pipe from the exhaust manifold. If there is room, you do not have to remove the exhaust manifold separately. This depends upon clearance between the exhaust manifold and the frame or chassis. Remove any accessories such as air conditioning or AC generator that attach to the head. Remove the EGR inlet tube, spark plug wire brackets, spark plug wires, any wiring attaching to sensors in the head and wiring that attaches to the coils if they mount on the rocker arm covers. Remove the retaining bolts for the rocker arm covers and lift them off the head.
Remove the valve pushrods. Loosen the rocker arm retaining bolts if necessary to give you clearance to get them out. Remove the head bolts with the correct sized socket. Carefully note which length of head bolt came from which hole. Remove the cylinder head from the engine block. Remove the head gasket from the cylinder block. Clean the carbon deposits from the combustion chamber and the top of the pistons using compressed air. Clean the rocker arm cover gasket surface, the intake manifold gasket surfaces, the head, and the cylinder block surfaces with the non-metallic scraper. Check the engine block surface and the head surface for flatness with the straight edge. If they are not flat, you may need machine shop work for correct installation.
Place the head gasket on the cylinder block over the dowel pins to hold it in place. Do not use any sealers. Carefully place the cylinder head on the engine block. Coat the threads of new head bolts with sealing compound. Install them finger tight. Torque the bolts to 22 foot-pounds, working from the inside out. Use the torque angle meter to measure how much to tighten the bolts in the next stage. The torque angle meter measures how far the bolt has turned from start to finish in degrees. Tighten the short bolts 55 degrees, the medium bolts 65 degrees and the long bolts 75 degrees.
Install the other components that you removed using the reverse procedure of installation. Fill the engine with coolant. Start the engine, and let it run to warm up. When the thermostat opens, the coolant level will drop in the radiator. Finish topping off the coolant at that time.
Be certain to clean the gasket surfaces properly. Use care when cleaning them not to damage, gouge or make valleys in the mounting surfaces. A combination torque wrench/torque angle meter will allow you to tighten the head bolts to the correct torque, then turn the bolts the correct amount of degrees in one motion with one tool. Consider purchasing or borrowing one to complete this repair.
Always use new head bolts, and be certain to use the described torque to yield tightening procedure. This allows the threads to stretch correctly. Be certain to clean the bolt holes of any debris. Debris in the bolt holes can cause inaccurate torque readings when tightening head bolts.
Tips and warnings
- Be certain to clean the gasket surfaces properly. Use care when cleaning them not to damage, gouge or make valleys in the mounting surfaces.
- A combination torque wrench/torque angle meter will allow you to tighten the head bolts to the correct torque, then turn the bolts the correct amount of degrees in one motion with one tool. Consider purchasing or borrowing one to complete this repair.
- Always use new head bolts, and be certain to use the described torque to yield tightening procedure. This allows the threads to stretch correctly. Be certain to clean the bolt holes of any debris. Debris in the bolt holes can cause inaccurate torque readings when tightening head bolts.
Things you need
- Standard and metric sockets
- Metric combination wrenches
- Replacement head gasket set
- Carbon scraper
- Straight edge
- Drain pan
- Torque angle meter
- Torque wrench
- New head bolts
- Head bolt sealant
- Marking pen
- Spark plug boot pullers
- Compressed air and blow gun