No, supposed to be a difficult one! I am fascinated by how the valve is driven though since it would appear to be going the wrong way, I think I read somewhere the housing holds 2 piston valves but I can't picture that. The Weir (sp?) type looks easier!
Andrew, after building a couple of small ST engines when I started model engineering I bought the set of pump castings with rather niave enthusiasm, with experience it still looks a stinker, don't know whether to try it or flog the castings on Ebay, I've enough to keep me amused with the Simplex! Ron