While smaller and seemingly less complicated than an automobile's engine, a motorcycle engine is still a complex arrangement of components. Where these components meet, gaskets are used to create seals to prevent the leakage of lubricants, coolants and gases. Due to a number of factors such as age, frequency of use, over pressure and the constant heating and cooling cycles of normal use, gaskets can and will eventually fail. A failed gasket can cause a minor oil leak or a catastrophic coolant leak, and any gasket that has failed should be immediately replaced to ensure the longevity of your motorcycle engine.
Remove the exhaust headers, fuel tank and any fairings or obstructions per the instructions in your shop manual. For liquid-cooled motorcycles, drain coolant per the instructions in your shop manual. Set parts aside in a safe place to prevent damage.
Loosen the cylinder head bolts and gently remove the cylinder head. Remove the old gasket and use the gasket scraper to remove any gasket remnants from the cylinder and cylinder-head gasket surfaces.
Lightly coat the new gasket with gasket dressing and place it on the gasket surface of the cylinder. Carefully replace the cylinder head and cylinder head bolts. Tighten the cylinder head bolts to the torque specs outlined in your shop manual.
Replace the exhaust headers, fuel tank, fairing and any other part you removed to access the cylinder head. For liquid-cooled motorcycles, refill the cooling system with fresh coolant per the instructions in your shop manual.
If your motorcycle is old enough or rare enough, parts like gaskets can be scarce. If you can't find a proper gasket for your motorcycle, you can make one out of gasket paper which can be found at any auto parts store.
Be careful not to scratch or gouge the gasket surfaces with the gasket scraper. Damage to the gasket surfaces can prevent the gasket from sealing correctly, and lead to continuing engine problems and possible severe engine damage. Use only a tiny amount of gasket dressing. Overuse of gasket dressing can clog important channels or seep into combustion chambers, which will cause severe engine damage. This is not an easy task nor one for an inexperienced mechanic. Some motorcycles will require that the engine is removed from the frame to access the head gasket. Only experienced mechanics should attempt to replace a gasket that requires engine removal.