The design intent isn't known to me, but I think it is registration, and secondly to erect a barrier so as not exposing a copper gasket to combustion flames, which could lead to glowing and produce self-ignition. Cylinder head gaskets for cars usually have a steel ring next to the combustion chamber (the composite gasket for Nortons also has this). Early 1966, AMC decided to remove the spigot. Why the copper head gasket still works without a steel ring is a mystery to me, but I guess the head design causes a layer of less heated gases which shield the gasket from direct exposure to really hot combustion gases. Someone here may have studied this.
- Knut
