Repairs, rebuilds, or overhauls major assemblies of internal combustion automobiles, buses, trucks or tractors. Work involves most of the following: Diagnosing the source of trouble and determining the extent of repairs required replacing worn or broken parts such as piston rings, bearings, or other engine parts; grinding and adjusting valves; rebuilding carburetors; overhauling transmissions; and repairing fuel injection, lighting, and ignition systems. In general, requires rounded training and experience usually acquired through a formal apprenticeship or equivalent training and experience.