These Cylinder Heads are Completely new castings, machined and O-Ringed.. Our heads have all new valves, springs, guides, retainers and locks.. All our heads are machined to our specs to guarantee No valve to piston contact. Our heads also have a pressed in Hardened valve seat to eliminate any cracking. Our valves and springs are made proprietary to our specs. These heads are direct bolt on with no modifications required. The Aircraft grade, hardened stainless wire O-ring will help seal and bite into the head gasket to eliminate head gasket Failure. We do sell larger valves and heavier valve springs for race applications. If your looking for a custom cylinder head setup please give us a call..