To put it simply, it is the combination of different components that makes up the combustion engine. The components are block, pistons, heads, and valves. When all these parts are put together, it makes the engine. Also, there are other essential parts such as fuel system, electrical system, and many more. Now let us break down the parts of the outboard. For more details visit, www.outboardclinic.com/remanufactured-powerheads/