A high efficiency uniflow steam engine having automatic inlet and exhaust valves rather than camshaft operated valves includes an electromagnet and cooperating armature that actuates a cutoff control valve for closing a steam inlet valve at any time selected to cut off the flow of steam to the cylinder. Approaching the end of the exhaust stroke, e.g., about 0.12 inch before TDC the cylinder can be sealed to thereby compressing the remaining residual steam down to a minute clearance approaching zero, for example, 0.020 inch raising cylinder steam pressure enough to open the steam inlet valve without physical contact between the piston and the steam inlet valve eliminating tappet noise, shock and wear.