Gaskets are designed to fill mating surfaces on engine parts and create a seal that prevents leakage. Although they are important components of your motorcycle, you don't give them a second thought until you discover a giant leak on the floor of your garage. Gaskets are made from paper, fiber, metal or rubber. Four-stroke head gaskets are usually made of multi-layer steel while most two-stroke engines use O-ring head gaskets.
Before you install a new gasket, the old gasket must be removed and the surface cleaned and checked for flatness. It's important not to scratch or mar the surface, so gasket scrappers and razor blades must be used with care. An oil stone (also known as a sharpening stone) can be used to remove stubborn remnants and resurface the finish if it becomes scratched or damaged. There are a variety of chemical solutions available that are designed to remove old gaskets, but they can be a mess if not used properly. Clean the surface with acetone, lacquer thinner or other clean-drying solvent once the old material has been removed. Make sure the old material hasn't strayed into other areas and contaminated your engine. Once the surface is clean and free of old gasket material, check for warpage with a straight edge or surface plate. Resurface if necessary or replace if the surface is too far out or specifications.
Tighten and torque nuts and bolts in the proper sequence to ensure that the gasket seals. Often new bolts are required because threads will become stretched over time. You can check to see if the threads have stretched by measuring them with a thread pitch gauge. Gaskets rarely require sealant, which should only be used if the manufacturer specifies or in extreme cases. O-ring head gaskets don't last as long as metal gaskets and should be checked for leakage and/or replaced frequently.