The job duties of an engine builder involve working to design, build, improve, assemble, and test engines. In this career, you usually work in the automotive industry, though you could also design engines for aerospace, manufacturing, or a variety of other industries. Your duties as an engine builder may include engine teardown and rebuilding, as well as creating new engines. Your employer may also expect you to work on a specific aspect of an auto design project, such as the transmission. In some positions, you may add components and inspect engines to ensure proper functionality.