Replacing a head gasket on a Nissan 240SX is not difficult. The project takes some time to do, which is why if you take the car to the repair garage, the repair costs are high. Still, this is a project that you can do yourself, in your garage or driveway. You will want to set aside an entire weekend for the project so that you do not feel as if you have to rush to reassemble the engine.
Disconnect the negative cable from the battery using a wrench to loosen the nut. Turn the crankshaft until the no. 1 piston is at top dead center using a wrench. The no. 1 piston is at top dead center when you line the timing marks up on the engine with that on the pulley. Do not turn the engine backward to get on the mark. If you pass it, go around another turn until you reach the mark again. Open the valve on the bottom of the radiator and drain the coolant into the drain pan.
Remove the radiator and heater hoses using a screwdriver to loosen the hose clamps. If the car has an air conditioner, unbolt the AC compressor and move it to the side using a socket and ratchet. Do not disconnect the refrigerant lines on the compressor. Unbolt the alternator using a socket and ratchet and move it to the side. Remove the power steering pump from the engine. Set the pump aside. It is not necessary to disconnect the hose on the pump.
Label each of the spark plug wires with the marker and masking tape noting the proper location of each one. Unplug each spark plug wire by grasping the boot and pulling it off. Pulling by the wire will damage the filament. Disconnect the throttle linkage from the throttle body by unhooking it. Disconnect the air cleaner and housing and remove it from the engine using a wrench. Remove the spark plugs using a socket and ratchet.
Relieve the pressure from the fuel system by opening the valve on the fuel rail. Label the electrical wires and vacuum hoses using the marker and masking tape. Disconnect the wires and vacuum hoses by unplugging them from their fittings. Disconnect the EGR tube from the rear of the engine by loosening the clamp. Loosen the clamps on the air exhaust induction tubes using a screwdriver and remove them.
Disconnect the exhaust pipe from the manifold with a wrench. Disconnect the PCV valve from the rear of the engine. Remove the valve cover using a socket and ratchet to remove the bolts. Remove the valve cover gasket carefully if you intend to use it again. Mark the relationship of the camshaft sprocket to the timing chain using a marking crayon. Doing this allows you to avoid trying to line up factory timing marks.
Remove the camshaft sprocket using a socket and ratchet. Hold the other end of the camshaft using a wrench of the proper size to keep it from turning when you are removing the sprocket bolts from the shafts. Loosen the cylinder head bolts starting from the ends and working your way in using a socket and ratchet. Remove the cylinder head from the engine block. You may have to tap it with a rubber mallet to break it free from the engine block.
Remove and discard the old head gasket. Take the cylinder head to an automotive machine shop to have it resurfaced before you reassemble the engine. This is important. The new head gasket may fail if the face of the cylinder head is not completely smooth and warp-free. Ensure the engine block is clean and damage-free before you place the new head gasket on it.
Place the new head gasket on the engine block, making sure the right side is face-up. The gasket will be marked noting the proper placement. Place the cylinder head on the engine block gently so that you do not damage the new gasket. Line the cylinder head up and loosely install the cylinder head bolts. Temporarily tighten the right and left cylinder head bolts to 14 foot-pounds using a torque wrench. Install the camshaft sprocket and line up the marks you made.
Tighten the sprocket bolt with the socket and ratchet. Tighten the cylinder head bolts with the torque wrench in three steps as follows:
Step 1: Tighten the bolts to 20 foot-pounds.
Step 2: Tighten the bolts to 40 foot-pounds.
Step 3: Tighten the bolts to 58 foot-pounds.
Install the spark plugs and tighten them with a socket and ratchet. Take care that you do not over-tighten, which will damage the threads in the cylinder head. Install the valve cover gasket and the valve cover. Tighten the valve cover bolts using the socket and ratchet. Plug in the PCV valve. Connect the exhaust pipe to the exhaust manifold and tighten the bolts with a wrench. Connect the air exhaust induction tubes to the exhaust manifold.
Install the EGR tube to the rear of the engine. Connect the throttle linkage to the throttle body. Install the air cleaner to the engine. Connect the fuel lines and tighten the fittings with a wrench. Install the vacuum lines and electrical leads according to the labels you made when removing them. Install the power steering pump and tighten the bolts with a wrench. Install the alternator and AC compressor. Adjust the belt tension so that you can depress it 1/2 inch.
Reconnect the heater and radiator hoses. Tighten the clamps with a screwdriver. Fill the radiator and reservoir with fresh engine coolant. Connect the negative cable to the battery and tighten the terminal nut with a wrench. Start the engine and check the work area for leaks.
