Consult the service manual or gasket manufacturer's instructions for the tightening sequence and torque values for the engine's head gasket. Then, using a torque wrench, tighten the head bolts slowly and in the correct sequence, using three to five rounds to completely tighten the bolts to the correct torque. Using this technique avoids distorting the head and creates an evenly sealed gasket.
Before installing the head bolts, clean them thoroughly with a wire brush. Examine the head bolts' threads for any signs of damage or wear, and replace any worn bolts. Also, clean the bolt hole threads in the engine block. Verify that the used head bolts are all the same length because head bolts can stretch over time. Never reuse torque-to-yield head bolts, which always stretch due to their unique design.
Lubricate the bolts with engine oil if the head bolts screw into blind holes, and make sure you can easily twist the head bolts into the correct hole with your fingers. If it requires any force to fit the head bolt into the hole, replace that bolt. Use flexible sealer to coat the head bolts if they reach the coolant jacket. If the cylinder heads are aluminum, make sure to use steel washers to help distribute the force.
For engines that need retorquing after installation, run the vehicle until it reaches the standard operating temperature, then turn off the car. Retighten the head bolts using the same sequence while the engine is still warm, unless it is an aluminum head block. Then, you should wait until the engine cools completely before retorquing the head bolts.