Replacing a head gasket

Head gasket replacement is not a job for the average do-it-yourselfer. While a head gasket expiring due to old age is rare, it usually means everything else is worn out to the point of replacement as well. Cracking the head off the engine and peering inside may reveal that everything else got fully cooked, too. The best way to prevent head gasket failure is to keep the cooling system in top working order and make sure the engine is in tune and running correctly. The failure of a $5 thermostat or $3 coolant hose can cause thousands of dollars in engine damage in a hurry.

How-to tips

The following are a few general tips to changing a head gasket. For vehicle-specific head gasket replacement procedures, always consult a service manual.

Step 1: Getting down to the head gasket can be an involved process. Always mark and index everything before removal. In this case, it was easier to remove the exhaust manifold, head and intake as a unit. A service manual is the first and most important tool in the toolbox.

Step 2: Check the head and block for flatness. A machined straight edge across the surface and feeler gauge will reveal all. The service manual will provide specifications. Blocks or heads out of specification must be sent out to the machine shop and be repaired. The machine shop will also be able to check for cracks.

Step 3: Prepare the surface. Never use anything that will remove metal. Be careful not to scratch the deck of the block or mounting surface of the head. While it may seem like a good idea to use a scrubber pad connected to a power tool, the surface irregularities created can cause sealing problems down the road.

Step 4: Chase the head bolt or stud holes with a tap or thread chaser to remove any crud and prepare the threads. Use compressed air to blow out any stragglers. Correct head bolt torque is of the utmost importance. Any interference can throw off the torque readings.

Step 5: Prefit the head gasket in the correct orientation. Never use sealant unless specifically required by the manufacturer. Head gaskets that require sealant will usually come so equipped. The service manual will outline sealant locations and requirements.

Step 6: Correct bolt tightening sequence and torque is key to proper head gasket sealing. Use new bolts if required. Coat head bolt threads with some engine oil before installing. Always follow tightening sequence and torque instructions to the last detail.