The Closed Rankine cycle steam powerplant is currently being re-examined as a low exhaust emission alternative to a gasoline spark ignition engine for use in automobiles and other vehicles. The paper summarizes the progress to date on the reciprocating steam expander component development program sponsored by U.S. Environmental Protection Agency under EPA Contract 68-04-0004. The principal components reviewed are: pistons, ring/liner combinations, valve train, series poppet valves for variable admission of steam to the cylinders and recompression steam relief valve. The current state of the art of automotive technology was used in component development work. Temperature and pressure measurement techniques are also described.