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.

1.1. Key Terms

compacted graphite iron (CGI) A material produced from powdered iron alloys squeezed into molds at high pressures and then heated to bond the metal particles together; also known as sintered graphite.

creep The movement of a cylinder head across the cylinder block deck when thermally cycled. When heated and cooled, the head expands and contracts at a different rate across the block deck by sliding over the head gasket.

cross flow cylinder head A head design with the intake and exhaust manifolds located on opposite sides of an in-line engine to improve engine breathing characteristics.

cylinder head gasket The component that maintains the seal around the combustion chamber at peak operating temperatures and pressures and that keeps air, coolants, and engine oil in their respective passages over all temperatures and pressures.

in-block camshaft An engine that has only the valves, rocker levers, and bridges located in the cylinder heads above the piston; the camshaft is located in the engine block. The cam may be a low- or high-mounted type; also known as a pushrod engine.

multilayer steel (MLS) gasket A method of sealing the cylinder head to the engine block using multiple thin layers of cold-rolled, spring-grade stainless steel coated with elastomeric (rubber) material.

overhead camshaft engine An engine that has the camshaft located in the cylinder head.

parallel flow head A head design that features intake and exhaust manifolds on the same side of the engine and short, large ports that are joined together to provide a more compact engine design with adequate airflow to the cylinders; also known as the uniflow design.

reverse flow cylinder head A cylinder head with no exhaust manifolds on the outside of the cylinder head; instead, short exhaust runs are fed directly to the turbocharger located in the V between the cylinder banks.

scissor gear Two separate, spring-loaded gears incorporated into a single drive gear that meshes under tension with a drive gear with no clearances. The gear is designed to reduce noise from gear rattle caused by torsional vibration.

torque-to-yield (TTY) bolts Cylinder head bolts that are tightened past their yield strength or elastic point; when tightened to specification, they stretch to a point just over precisely calibrated yield strength and not to the tensile where the bolt will break.

torque-turn method A method that requires a bolt to receive an initial preload using a torque wrench; afterward, the bolt is turned several additional degrees, flats, or turns; also known as the torque-plus-angle method.

torsional vibration The speeding up and slowing down of the crankshaft caused by alternating compression and power strokes of the engine cylinder.

Tyndall blue The blue-colored exhaust smoke created by a wavelength of light passing through microscopic-size exhaust particles. Oil and fuel droplets in the exhaust most frequently create the blue tint in the exhaust smoke.

valve overlap The angle in crankshaft degrees at which both the intake and the exhaust valves are open; overlap occurs at the end of the exhaust stroke and at the beginning of the intake stroke.