Bus and truck mechanics and diesel engine specialists, repair and maintain the diesel engines that power transportation equipment. Other diesel technicians and mechanics work on other heavy vehicles and mobile equipment, including bulldozers, cranes, road graders, farm tractors, and combines. The U.S. Department of labor admits that many diesel mechanics receive on the job training, but it is quick to point out that your prospects will improve tremendously if you complete a formal diesel engine training program. These courses tend to last anywhere from 6 months to 2 years. Given how complex engines are becoming (some have computer chips these days), you will definitely benefit from formal classes. Besides, most employers would prefer to hire a certified mechanic as opposed to an eager beginner.