Head gasket problems are common with older air-cooled engines when the gaskets become brittle due to excessive heat. A bad head gasket can lead to oil leaks and poor engine performance. In some cases it is possible to repair the gasket as long as the metallic rings that seal the cylinder sleeves are not broken. In other cases, the only method of repair is replacing the gasket. In either event, it is necessary to first remove the cylinder head in order to access the gasket.
Refer to the owner's manual illustrations and instructions and remove the components necessary to access the rocker cover and rocker arm assembly at the top of the engine. Depending on the motorcycle, components may include the gas tank, fairings or radiator and cooling lines. Components are removed using metric sockets and a ratchet to remove mounting bolts.
Locate the hex-head bolts that secure the rocker cover to the rocker arm assembly at the top of the engine. Depending on the motorcycle, there may be four, or as many as eight rocker cover bolts. Remove the bolts counterclockwise with a socket and ratchet. Set the bolts and the rocker arm cover aside.
Pull the spark plug wires off the spark plugs. Use a spark plug wrench and ratchet to remove the spark plugs counterclockwise from the cylinder head.
Push the kick-starter slowly or use the electric starter intermittently to rotate the engine crank as you observe the timing chain on the timing sprocket at the centre of the rocker arm assembly. Rotate the engine crank until the timing chain master link is at the top of the timing sprocket.
Cut two lengths of 14-gauge wire 24 inches long. Set the pieces of wire nearby. Remove the timing chain master link clip using a screwdriver. Save the clip. Hold the chain in place on the sprocket on each side of the master link. Remove the master link from the chain by pushing it out as you continue to hold the ends of the chain in place on the sprocket. Set the master link aside.
Attach one end of each piece of 14-gauge wire securely to each of the chain loops where the master link was removed. The wire is needed to lift the timing chain back into place during the reassembly of the top-end. Without the wire the timing chain will fall into the crankcase. Lift the ends of the timing chain off the timing sprocket and secure each wire to a point on the motorcycle frame.
Remove the hex-head bolts that secure the rocker arm assembly and cylinder head to the top of the cylinder by turning each counterclockwise with the socket and ratchet. Pull the bolts straight up and out and set them aside.
Lift the rocker arm assembly and cylinder head off the cylinder. Temporarily remove each of the 14-gauge wires from the frame so you can completely remove the rocker arms and cylinder head. Reconnect each wire as before. Set the rocker arm assembly and cylinder head aside.
Inspect the head gasket atop the cylinders. Look for cracks in the metallic sleeves that surround the edges of the cylinder bores. If the sleeves are damaged or deteriorated the gasket must be replaced. If the sleeves are intact, proceed to the following steps.
Turn the rocker arm and cylinder head over and inspect the flat edges of the head. Look for irregular colouration, such as darker or lighter areas that signify a hole or tear in the head gasket material.
Re-inspect the head gasket and locate the holes or tears. Apply a uniform layer of gasket cement to the gasket material at the damaged area using the provided spreader or a plastic putty knife. Allow the gasket cement to dry completely.
Place the rocker arm assembly and head onto the cylinder. Lift the ends of the timing chain in place on the timing sprocket using the 14-gauge wires. Hold the ends of the chain on the sprocket, remove each wire and connect the ends of the chain with the master link and chain clip.
Refer to the owner's manual for torque specifications and torque the rocker arm assembly and head bolts using a torque wrench. Attach the rocker arm cover using the saved bolts. Reinstall the spark plugs and attach the plug wires. Reattach any removed components.
Ask an experienced mechanic to oversee the engine work and provide assistance. Refer to a replacement gasket by year and model of the motorcycle.
Do not attempt motorcycle engine work without the proper tools.