Chapter 09: Final Review & Key Terms

1. Ready for Review

• The cylinder head is a metal casting that attaches to the top of the cylinder block and seals the combustion chamber so that the engine can develop and contain compression and combustion pressure.
• Cylinder heads are commonly made of cast iron alloys because of their superior strength, ease of manufacture, machinability, and capability to withstand high temperatures; aluminum and compacted graphite iron are other materials commonly used for cylinder heads.
• Because intake and exhaust port arrangements influence gas flow and turbulence, or swirl, into the cylinders, the configuration of these ports is important for reducing emissions and used to classify cylinder heads.
• Cylinder heads can also be classified by their number of pieces; single-piece cylinder head castings and multiple-piece cylinder heads both have advantages and disadvantages.
• Cylinder heads are further classified by the arrangement of the valve train mechanism; the camshaft arrangements in diesel engines are commonly one of two types—overhead camshaft or in-block camshaft.
• Intake and exhaust valves allow gases into and out of the cylinder; diesel engines usually have two or four valves per cylinder, but a number of engines may use three or five valves.
• Pushrods transmit the cam actuation force from the followers to the rocker levers.
• Rocker arms convert the linear change of the cam profile to the reciprocating motion used to open and close the valves.
• To actuate more than one valve with a single rocker lever, most four-valve engines use a crosshead, also called a yoke or bridge , to exert the camshaft force against the valve stem.
• Camshafts are critical components to engine performance because they control the gas dynamics or engine breathing characteristics.
• Because of the higher cylinder pressures, consistent bolt clamping force is a critical maintenance issue for diesel engines.
• In some applications or high-performance modifications, studs rather than bolts are used.
• The cylinder head gasket is arguably the most important seal in the diesel engine; to prevent warping of cylinder heads, damaged bolts and threads, and gasket leakage, adequate and consistent clamping force of the cylinder head is necessary.
• To coordinate the movement of the crankshaft with the camshaft and the valves, a geartrain or valve timing mechanism is used; the geartrain may also transfer power from the crankshaft to operate fuel injection apparatuses, lubricating mechanisms, power steering and coolant pumps, accessory drive mechanisms, and even power take-off pumps.
• Pendulum dampers provide torsional control by producing forces that directly cancel the forces producing torsional vibration.