Engine Parts
An automotive engine generates power through the combustion of air and fuel within a sealed cylinder. The essential components of an engine cylinder assembly, including the piston, cylinder, engine block, and cylinder head, are depicted in the diagram below. The cylinder, a cylindrical metal tube housed within the engine block, serves as the container for the combustion process. The cylinder head, a metal cover at the top of the cylinder, houses valves that regulate the flow of air and exhaust gases during engine operation. In a four-stroke cycle engine, these valves include intake valves and exhaust valves.
The diagram presented illustrates a section of a four-stroke engine, highlighting the positioning of key components such as the cylinder, piston, connecting rod, crankshaft, combustion chamber, cylinder head, spark plug, intake valve, and exhaust valve.
These valves, known as poppet valves, are actuated in an upward and downward motion to regulate the opening and closing of intake and exhaust valves in an engine. The intake valve permits the entry of the air-fuel mixture into the cylinder, while the exhaust valve allows the release of exhaust gases resulting from combustion. When both valves are shut, the cylinder is tightly sealed. The piston, a cylindrical metal component, operates within the cylinder to facilitate the engine’s movement.
When the piston reaches the top of the cylinder, it creates an open space known as the combustion chamber in the cylinder head. In this area, a combination of air and gasoline undergoes combustion to generate power, a process commonly referred to as combustion.
It is important to recognize that the spark plug is securely fastened into a threaded aperture within the cylinder head. The tip of the spark plug extends beyond the cylinder head and into the combustion chamber, where it serves the critical function of generating sparks to ignite the air and fuel mixture within the cylinder, triggering combustion.
The piston is linked to the crankshaft via the connecting rod, enabling the transfer of the piston’s vertical movement to the crankshaft. This mechanism ultimately transforms the reciprocating motion of the piston into rotational motion.
This deconstructed depiction of an engine showcases the primary components that constitute the engine.
Specific terminology is utilized to denote the precise location of the piston within the cylinder. At the lowest point in the cylinder, the piston is referred to as being at bottom dead center (BDC), while at the highest point in the cylinder, it is termed as being at top dead center (TDC). The overall distance traveled by the piston from the top to the bottom of the cylinder is known as the stroke.
DOHC Automotive Engine with Front Timing Cover Removed (Courtesy of James Halderman)
The majority of contemporary vehicles are equipped with four-stroke engines. The illustration displayed depicts a dual overhead camshaft (DOHC) automotive engine with the front timing cover removed, revealing the intricately assembled timing chain.
Engine Sections
Due to the complexity of an engine and the multitude of components it contains, it is beneficial to divide the engine into two distinct sections for discussion: the lower end and the upper end. These sections are named based on their placement within the engine. The lower end, also known as the bottom end, includes components such as the engine block, cylinders, pistons, connecting rods, and crankshaft assemblies. These components work together to convert the vertical motion of the pistons into rotational motion, which powers the vehicle. The upper end of the engine comprises the cylinder head, valves, valve train components, manifolds, and engine covers. The primary function of the upper end components is to regulate the intake and exhaust of air and fuel mixture within the engine.
