The heads on your commercial or fleet diesel are one of the most integral parts of your engine. The heads are comprised of the valvetrain, exhaust ports, intake ports, and injector ports. In essence, a head’s purpose is to regulate and time the intake of fresh air, the release of exhaust, the compression of fuel and air that provides combustion, and the entry point for fuel into the cylinder. The head is where all the complex aspects of engine operation occur...without it, you just have a chunk of metal with pistons in it, and no way to make them move. Here’s what you need to know about your heads, from Harold's Used Auto Parts Inc in Philadelphia, PA.