In a piston engine, the cylinder head sits above the cylinders, [1] forming the roof of the combustion chamber. In sidevalve engines the head is a simple plate of metal containing the spark plugs and possibly heat dissipation fins. In more modern overhead valve and overhead camshaft engines, the head is a more complicated metal block that also contains the inlet and exhaust passages, and often coolant passages, Valvetrain components, and fuel injectors.
A piston engine typically has one cylinder head per bank of cylinders.
Most modern engines with a "straight" (inline) layout today use a single cylinder head that serves all the cylinders.
Engines with a "V" layout or "flat" layout typically use two cylinder heads (one for each cylinder bank), however a small number of 'narrow-angle' V engines (such as the Volkswagen VR5 and VR6 engines) use a single cylinder head spanning the two banks.
Most radial engines have one head for each cylinder, although this is usually of the monobloc form wherein the head is made as an integral part of the cylinder. This is also common for motorcycles, and such head/cylinder components are referred to as barrels.
Some engines, particularly medium- and large-capacity diesel engines built for industrial, marine, power generation, and heavy traction purposes (large trucks, locomotives, heavy equipment, etc.) have individual cylinder heads for each cylinder. This reduces repair costs as a single failed head on a single cylinder can be changed instead of a larger, much more expensive unit fitting all the cylinders. Such a design also allows engine manufacturers to easily produce a 'family' of engines of different layouts and/or cylinder numbers without requiring new cylinder head designs.
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| Engine type (in chronological order) | Camshaft location | Intake valves location | Exhaust valves location |
|---|---|---|---|
| Sidevalve (flathead) | Block | Block | Block |
| Inlet over exhaust (IOE) | Block | Head | Block |
| Overhead valve (OHV) | Block | Head | Head |
| Overhead camshaft (OHC) | Head | Head | Head |
In a flathead (sidevalve) engine, all of the valvetrain components are contained within the block, therefore the head is usually a simple plate of metal bolted to the top of the engine block. Sidevalve engines were once universal but are now largely obsolete in automobiles, found almost exclusively in small engines such as lawnmowers, weed trimmers and chainsaws.
Intake Over Exhaust (IOE) engines combined elements of the sidevalve and overhead valve designs. Used extensively in American motorcycles in the early 1900s, the IOE engine remained in production in limited numbers until the 1990s. IOE engines are more efficient than sidevalve engines, but also more complex, larger and more expensive to manufacture.
In an overhead valve (OHV) or overhead camshaft (OHC) engine, the cylinder head contains several airflow passages called ports; intake ports deliver the fuel+air intake charge from the intake manifold to the combustion chamber, and exhaust ports route combustion waste gases out the combustion chamber to the exhaust manifold. Valves open and close the ports, with the intakes offset fore-and-aft from the exhausts. The head also contains the spark plugs, and on water-cooled engines, the coolant passages.
A single camshaft located in the engine block uses pushrods and rocker arms to actuate all the valves.
OHV engines are typically more compact than equivalent OHC engines, and fewer parts mean cheaper production, but they have largely been replaced by OHC designs, except in some American V8 engines.
An overhead camshaft (OHC) engine locates the camshaft(s) in the cylinder head above the combustion chamber. Eliminating pushrods lessens valvetrain inertia and provides space for optimized port designs, both providing increased power potential.
In a single overhead camshaft (SOHC) engine, the camshaft may be seated centrally between valve rows, or directly above a single row of valves (replacing rocker arm actuation with tappets). SOHC engines were widely from the 1960s to 1990s. (eliminating pushrods but still utilizing rocker arms)
Double overhead camshaft (DOHC) engines seat a camshaft directly above each row of offset valves (intakes inboard, exhausts outboard). [2] DOHC designs allow optimal crossflow positioning of valves to provide higher-RPM operation. They are typically larger in size (especially width) than equivalent OHV or SOHC engines. Even though more components raise production costs, DOHC engines seen widespread use in automobile engines since the 1990s.
A poppet valve is a valve typically used to control the timing and quantity of petrol (gas) or vapour flow into or out of an engine, but with many other applications.
A camshaft is a shaft that contains a row of pointed cams in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines, mechanically controlled ignition systems and early electric motor speed controllers.
A hemispherical combustion chamber is a combustion chamber in the cylinder head of an internal combustion engine with a domed "hemispheric" shape. An engine featuring this type of hemispherical chamber is known as a hemi engine. In practice, shapes less than a full hemisphere are typically employed, as are variations of a true hemispheric profile. The primary advantage of such shapes are increased compression and very large intake and exhaust valves ; the primary disadvantages are complex valve trains and expense.
A crossflow cylinder head is a cylinder head that features the intake and exhaust ports on opposite sides. The gases can be thought to flow across the head. This is in contrast to reverse-flow cylinder head designs that have the ports on the same side.
The LA engine is a family of overhead-valve small-block 90° V-configured gasoline engines built by Chrysler Corporation between 1964 and 2003. A replacement of the Chrysler A engine, they were factory-installed in passenger vehicles, trucks and vans, commercial vehicles, marine and industrial applications. Their combustion chambers are wedge-shaped, rather than polyspheric, as in the A engine, or hemispheric in the Chrysler Hemi. LA engines have the same 4.46 in (113 mm) bore spacing as the A engines.
An overhead camshaft (OHC) engine is a piston engine in which the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion chamber in the engine block.
An overhead valve engine, abbreviated (OHV) and sometimes called a pushrod engine, is a piston engine whose valves are located in the cylinder head above the combustion chamber. This contrasts with flathead engines, where the valves were located below the combustion chamber in the engine block.
A multi-valve or multivalve engine is one where each cylinder has more than two valves. A multi-valve engine has better breathing, and with more smaller valves may be able to operate at higher revolutions per minute (RPM) than a two-valve engine, delivering more power.
A flathead engine, also known as a sidevalve engine or valve-in-block engine, is an internal combustion engine with its poppet valves contained within the engine block, instead of in the cylinder head, as in an overhead valve engine.
A tappet or valve lifter is a valve train component which converts rotational motion into linear motion in activating a valve. It is most commonly found in internal combustion engines, where it converts the rotational motion of the camshaft into linear motion of intake and exhaust valves, either directly or indirectly.
The Honda F-Series engine was considered Honda's "big block" SOHC inline four, though lower production DOHC versions of the F-series were built. It features a solid iron or aluminum open deck cast iron sleeved block and aluminum/magnesium cylinder head.
A rocker arm is a valvetrain component that typically transfers the motion of a pushrod in an overhead valve internal combustion engine to the corresponding intake/exhaust valve.
A valvetrain is a mechanical system that controls the operation of the intake and exhaust valves in an internal combustion engine. The intake valves control the flow of air/fuel mixture into the combustion chamber, while the exhaust valves control the flow of spent exhaust gases out of the combustion chamber once combustion is completed.
The intake/inlet over exhaust, or "IOE" engine, known in the US as F-head, is a four-stroke internal combustion engine whose valvetrain comprises OHV inlet valves within the cylinder head and exhaust side-valves within the engine block.
A T-head engine is an early type of internal combustion engine that became obsolete after World War I. It is a sidevalve engine distinguished from the more common L-head by its valve placement. In T-head engines, the intake valves are located on one side of the engine block and the exhaust valves on the other. When viewed from the end of the crankshaft, especially in a cutaway view, the cylinder and combustion chamber resemble a 'T', leading to the name "T-head". In contrast, an L-head engine has all valves on the same side.
The Mercedes-Benz OM606 is a 3.0 litres (2,996 cc) inline-six cylinder (R6/I6) double overhead camshaft (DOHC) diesel engine with indirect injection manufactured by Mercedes-Benz between 1993 and 2001. It replaced the single overhead camshaft (SOHC) OM603 engine.
Designed by Aurelio Lampredi, the Fiat 124 engine first appeared in the all-new Fiat 124 in April 1966. The in-line four-cylinder engine comprised an iron block with an aluminium cylinder-head with pushrod actuated valves. The belt-driven design was ahead of its time when introduced. European production of the petrol versions ended with the Fiat 131 in 1984, but later diesel derivatives continued to be built until 1999. It did have a longer life in its twin-cam iteration, which continued in production until 2000. While originally of an overhead valve design, an overhead cam version was added to the facelifted 131 in 1981. The capacity was initially 1.2 L (1,197 cc), but eventually ranged between 1.2 and 1.9 L. There were also three SOHC diesel iterations of 1.4, 1.7, and 1.9 litres. The last versions of this engine to be built were the diesels. The 1.9 L (1,929 cc) direct-injected diesel version was the first direct-injection diesel to appear in a production passenger car, the Fiat Croma Turbo D i.d.
Weidely Motors Company was an early motor company based in Indianapolis, IN. Weidely started in 1915. It made engines for Premier, Chalmers, Cletrac crawlers and Owen Magnetic cars. They also made a V-12 engine for the 1917 Pathfinder and 1920 Heine-Velox, as well as the 1916-1918 Austin, Hal and Kissel cars.
