Engineworx Gasket Kit (Top Set) Yamaha YZ450F 14-17 Engineworx Top End Gasket Kits are the new leader in OEM replacement engine gasket kits. Kits include gaskets and seals necessary to rebuild the top end of your engine. All 4 Stroke head gaskets use Japanese stainless steel laminated head gasket and Viton valve seals, ensuring the best quality possible.