EMD 645

The EMD 645 is a family of two-stroke diesel engines that was designed and manufactured by the Electro-Motive Division of General Motors. While the 645 series was intended primarily for locomotive, marine and stationary engine use, one 16-cylinder version powered the 33-19 "Titan" prototype haul truck designed by GM's Terex division.

The 645 series was an evolution of the earlier 567 series and a precursor to the later 710 series. First introduced in 1965, the EMD 645 series remained in production on a by-request basis long after it was replaced by the 710, and most 645 service parts are still in production. The EMD 645 engine series is currently supported by Electro-Motive Diesel, Inc., which purchased the assets of the Electro-Motive Division from General Motors in 2005. EMD is currently owned by Progress Rail (since 2010).

In 1951, E. W. Kettering wrote a paper for the ASME entitled History and Development of the 567 Series General Motors Locomotive Engine, which goes into great detail about the technical obstacles that were encountered during the development of the 567 engine. These same considerations apply to the 645 and 710, as they are a logical extension of the 567C – by applying a cylinder bore increase for the 645, and a cylinder bore increase and a stroke increase for the 710 – to achieve a greater power output without changing the external size of the engines or their weight, thereby achieving significant improvements in power per unit volume and power per unit weight.

Due to emissions restrictions these engines have been gradually phased out for the four-stroke alternatives.