GM Powertrain Flint North (GMPT Flint North) was a General Motors automobile engine and components plant located at the Stewart Avenue exit of I-475 in Flint, Michigan . The plant consisted of several factories that combine to make the Flint North Powertrain plant. The 4,000,000-square-foot (370,000 m²) plant opened in 1905 as part of the Buick Motor Company, and was the last part of Buick City standing. The engine plant (Factory 36) portion of Powertrain Flint North closed in 2008. It is famous for building the GM 3800 engine, one of the longest-produced automobile engines in history.