Greetings Dale, I have a question regarding the piston valves which I hope you (or anyone) can shed some light on. I note Kozo's article in Live Steam (July/August) specifies 0.04 mm.,( 1 thou), for the clearance and advises thermal expansion will enable an adequate seal with minimal leakage. My question is, do you consider this close tolerance combined with expansion of the valve set up a 'molecular seal'? By this I mean the seal is brought about by the very thin film of water/oil on the surface of the valve head and wall of the valve chamber. I remember reading about molecular sealing somewhere but have forgotten where. I thought this design might be taking advantage of it and would be very interested in how effective it is. I do not have any of Kozo's books on other engines to help clarify his ideas further. There might be value for me here in overcoming the sealing issues relating to the disk engine I have some interest in. Regards Paul Gough.