Manufacturingautomotive powertrain components (engines and transmissions) is a complex task involving the integration of hundreds of components. Simulation is commonly applied in the design and implementation of such production systems. Examples of such systems are the crankshaft machining line, engine final assembly and transmission final assembly, to name a few. Invariably, different engine and transmission subassemblies are machined and assembled on separate systems.The completed sub-assemblies are then assembled to the engine or transmission main assembly. There are many areas within a powertrain assembly plant that show complicated behavior due to the varying nature of manufacturing processes. Not only the variation in process, but the schedules, availability of workers, and the performance of material handling equipment are only few of the factors contributing to the randomness in operation. Test areas where the final assembly is inspected for functionality present an example of such highly random operation. Simulation is a very useful tool for investigating the behavior of such complicated systems. This paper discusses the need for and uses of discrete event simulation in the design of manufacturing systems for powertrain assemblies. The benefits of such applications of simulation are illustrated by using a sample study of the final engine test and repair area.