Is there a standard industry name for the triangular 3-bolts fill neck plate at the top of the engine in Series 2 cars? its the one the radiator cap screws on to.
That is the header tank filler neck. It does not have a pressure cap, it has a blanking cap on it. I filed the top rim of mine to make it flat then made a thicker rubber gasket to seal it.
I had a small leak at the blanking cap on my SII and replaced it with one made by Waxstat, looks similar to the one in Clarke's photo. The Waxstat cap has a thicker rubber gasket than the cap I replaced, and it no longer leaks.
However, I do still have a leak from under the triangular plate. The parts diagram indicates use of a triangular shaped gasket up to engine number 8L14791 and then an o-ring after that. My engine number starts 8L165xxx, but I had a gasket and no o-ring. My plan is to take the tank off to clean up the neck area, then put in a new o-ring and use rtv or permatex between the triangular plate and header tank.
