A high efficiency uniflow steam engine having automatic poppet valves yieldably based by fluid such as steam held under pressure within a cavity in the engine and a cutoff control for closing a steam inlet valve at any time selected stops the flow of steam into the cylinder. Proximate the end of the exhaust stroke, around 0.12 inch before TDC the cylinder is sealed to thereby compress residual steam as the piston clearance approaches zero; typically, 0.020 inch which raises cylinder pressure enough to open an inlet valve without making physical contact to push the inlet valve open with the piston thereby eliminating a tappet type of noise, shock and wear.