An engine diagram shows the inner and outward working parts of the engine. It is helpful tool to your mechanic to rebuild your engine if you have to take it in. Engines vary in size and shapes.They also vary in horsepower, and to rebuild an engine properly to manufacturing specs an engine diagram is very helpful to have with you at this time. For more information on this subject click the link
. provided here. http://www.engine-repairs.com/engine_diagram.html