Optically-accessible engines provide valuable insight into in-cylinder combustion mechanisms and are widely considered an essential tool in fundamental internal combustion engine research. Here, a 2-piece Bowditch-type optical piston is developed as a replacement for a single-piece piston used in a 2 L, heavy-duty compression-ignition engine, which is convertible for use in both an optical and all-metal configuration. This piston was designed to provide long measurement durations, to simplify cleaning of the piston window, and to facilitate changes in piston crown geometry.A 2-piece piston architecture allows application of different piston bowl, crown, and compression ring geometries with minimal manufacturing and design cost. It was experimentally found that the cyclic loading experienced by piston rings permits the use of a lower grade material than plain bearing theory predicts. A set of 3 glass-filled PTFE compression rings were designed to replace the 2 conventional steel split-rings, resulting in improved gas sealing, reduced window fouling from lubrication grease, and longer testing intervals. The selection of these rings was validated by experimental measurement of break-in performance and pressure sealing. A new window cartridge arrangement protects the window during assembly, disassembly, and application of the gasket preload force. A finite element analysis was used to assess the static and fatigue stresses in all components, as well to provide an estimate of the heat transfer through the piston crown. This paper provides a method for the design and production of Bowditch-piston assemblies.