A cylinder head sliced in half shows two overhead camshafts—one above each of the two valves.

Overhead camshaft (OHC) valvetrain configurations place the camshaft within the cylinder heads, above the combustion chambers, and drive the valves or lifters directly instead of using pushrods. When compared directly with pushrod (or I-Head) systems with the same number of valves, the reciprocating components of the OHC system are fewer and in total will have less mass. Though the system that drives the cams may become more complex, most engine manufacturers easily accept the added complexity in trade for better engine performance and greater design flexibility. The OHC system can be driven using the same methods as an I-Head system, these methods may include using a timing belt, chain, or in less common cases, gears. Image File history File links Source copied from de:Bild:DOHC-Zylinderkopf-Schnitt. ... Image File history File links Source copied from de:Bild:DOHC-Zylinderkopf-Schnitt. ... The cylinder head from a GMC van. ... A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. ... A traditional reciprocating internal combustion engine uses valves to to control air and fuel flow into and out of the cylinders, facilitating combustion. ... For the fictional characters of the same name, see Camshaft (Transformers). ... The cylinder head from a GMC van. ... A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. ... For the ionic propulsion device, see Lifter (ionic propulsion device). ... A pushrod engine or overhead valve (OHV) engine is a type of piston engine that places the camshaft below the pistons (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine) and uses pushrods or rods to... A pushrod engine or overhead valve (OHV) engine is a type of piston engine that places the camshaft below the pistons (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine) and uses pushrods or rods to... A pushrod engine or overhead valve (OHV) engine is a type of piston engine that places the camshaft below the pistons (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine) and uses pushrods or rods to... A pushrod engine or overhead valve (OHV) engine is a type of piston engine that places the camshaft below the pistons (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine) and uses pushrods or rods to... Timing belt A timing belt, timing chain or cam belt is a part of an internal combustion engine that controls the timing of the engines valves. ... Roller chain and sprocket Roller chain or bush roller chain is the type of chain most commonly used for transmission of mechanical power on bicycles, motorcycles, and in industrial and agricultural machinery. ... Spur gears found on a piece of farm equipment. ...

Many OHC engines today employ Variable Valve Timing and multiple valves to improve efficiency and power. OHC also inherently allows for greater engine speeds over comparable cam-in-block designs. Variable valve timing, or VVT, is a generic term for an automobile piston engine technology. ... In automotive engineering, an engine is referred to as multi-valve (or multivalve) when each cylinder has more than two valves. ...

There are two overhead camshaft layouts:

• Single overhead camshaft (SOHC)
• Double overhead camshafts (DOHC)

Single overhead camshaft

A single overhead camshaft cylinder head from a 1987 Honda CRX Si.

Single overhead camshaft is a design in which one camshaft is placed within the cylinder head. In an inline engine this means there is one camshaft in the head, while in a V engine there are two camshafts: one per cylinder bank. Image File history File linksMetadata Download high-resolution version (1082x896, 532 KB) I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1. ... Image File history File linksMetadata Download high-resolution version (1082x896, 532 KB) I, the creator of this work, hereby grant the permission to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1. ... Year 1987 (MCMLXXXVII) was a common year starting on Thursday (link displays 1987 Gregorian calendar). ... This article is about the Japanese motor corporation. ... mk1 Honda Civic CRX The Honda Civic CRX, originally launched as the Honda Ballade CR-X in Japan, is a compact sports car manufactured by Honda. ... The cylinder head from a GMC van. ... A V engine is a common configuration for an internal combustion engine in which the pistons are aligned so that, if viewed along the line of the crankshaft, they appear to be in a V. Usually, two opposing pistons share one crank on the crankshaft. ...

The SOHC design has less reciprocating mass than a comparable pushrod design. This can allow for higher engine speeds, which in turn will increase power output for a given torque. The cam operates the valves directly or through a rocker arm as opposed to overhead valve pushrod engines, which have tappets, long pushrods and rocker arms to transfer the movement of the lobes on the camshaft in the engine block to the valves in the cylinder head. A pushrod engine or overhead valve (OHV) engine is a type of piston engine that places the camshaft below the pistons (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine) and uses pushrods or rods to... Torque applied via an adjustable end wrench Relationship between force, torque, and momentum vectors in a rotating system In physics, torque (or often called a moment) can informally be thought of as rotational force or angular force which causes a change in rotational motion. ... rocker arm This page meets Wikipedias criteria for speedy deletion. ... A pushrod engine or overhead valve (OHV) engine is a type of piston engine that places the camshaft below the pistons (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine) and uses pushrods or rods to... The cylinder head from a GMC van. ...

SOHC designs offer reduced complexity compared to pushrod designs when used for multivalve heads, in which each cylinder has more than two valves. An example of a SOHC design using shim and bucket valve adjustment was the engine installed in the Hillman Imp,(4 cylinder, 8 valve) a small early 1960s 2 door saloon car with a rear mounted alloy engine based on the 'Coventry Climax' FWMA race engines. Exhaust and inlet manifolds were both on the same side of the engine block, (thus not a crossflow cylinder head design).However this did offer excellent access to the spark plugs. A pushrod engine or overhead valve (OHV) engine is a type of piston engine that places the camshaft below the pistons (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine) and uses pushrods or rods to... In automotive engineering, an engine is referred to as multi-valve (or multivalve) when it has more than two valves. ... In engineering, a shim is a thin and often tapered or wedged, piece of material, used to fill small gaps or spaces between objects. ... Hillman Imp, with the engine cover and the rear window lifted The Hillman Imp was a compact, rear-engined saloon (US: sedan) automobile manufactured under the Hillman marque by the Rootes Group (later Chrysler Europe) from 1963 to 1976. ... A crossflow cylinder head is a cylinder head that features the intake and exhaust ports on opposite sides. ...

In the early 1980s Toyota and Volkswagen also used a directly actuated, SOHC parallel valve configuration with two valves for each cylinder. The Toyota system used hydraulic tappets while the Volkswagen system used bucket tappets with shims for valve lash adjustment. Of all valvetrain systems this is the least complex configuration possible. This article is about the automaker. ... Volkswagen AG (ISIN: DE0007664005), or VW, is an automobile manufacturer based in Wolfsburg, Germany. ...

Dual overhead camshaft

Overhead view of Suzuki GS550 head showing dual camshafts and drive sprockets.

A dual overhead camshaft (also called DOHC, double overhead cam, dual overhead cam, or twin cam) valve train layout is characterized by two camshafts being located within the cylinder head, where there are separate camshafts for inlet and exhaust valves. Typical automotive engines equipped with dual overhead camshafts can have from two to four camshafts in total, depending on the engine configuration. Image File history File linksMetadata Suzuki-GS550-DOHC.jpg‎ Engine head of a 1977 Suzuki GS550, clearly showing the dual overhead cams. ... Image File history File linksMetadata Suzuki-GS550-DOHC.jpg‎ Engine head of a 1977 Suzuki GS550, clearly showing the dual overhead cams. ... It was back in the 70s when Honda and Kawasaki basically divided the market for big road-going four-stroke fours. ... Twin cam of a 1977 Suzuki GS550 motorcycle. ...

Double overhead camshafts are not required in order to have multiple inlet or exhaust valves, but are necessary for more than 2 valves that are directly actuated (though still usually via tappets). Not all DOHC engines are multivalve engines — DOHC was common in two valve per cylinder heads for decades before multivalve heads appeared, however today DOHC is synonymous with multi-valve heads, since almost all DOHC engines have between three and five valves per cylinder, such as in the Toyota Corolla AE86 (16 Valve) or the Toyota Levin BZ-G (20 Valve). In automotive engineering, an engine is referred to as multi-valve (or multivalve) when it has more than two valves. ... In automotive engineering, an engine is referred to as multi-valve (or multivalve) when it has more than two valves. ...

History

DOHC straight-8 in a 1933 Bugatti Type 59 Grand Prix racer

The first DOHC engines were two or four valve per cylinder designs from companies like Fiat (1912), Peugeot Grand Prix (1913,4 valve), Alfa Romeo GP - (1914, 4 valve), 6C- 1925, Maserati (Tipo 26, 1926) and Bugatti (Type 51, 1931) and Audi. Most Ferraris used two valve per cylinder DOHC engines as well. Image File history File links Download high resolution version (2185x1295, 343 KB) 1933 Bugatti Type 59 Grand Prix From the Ralph Lauren collection on display at the Boston Museum of Fine Arts. ... Image File history File links Download high resolution version (2185x1295, 343 KB) 1933 Bugatti Type 59 Grand Prix From the Ralph Lauren collection on display at the Boston Museum of Fine Arts. ... A double overhead cam (also called a dual overhead cam, DOHC, or twincam) engine is a type of internal combustion engine where the camshafts that operate the intake and exhaust valves are mounted above the cylinders, and where there are separate camshafts for inlet and exhaust valves. ... 1933 Bugatti DOHC straight-8 in a Type 59 Grand Prix racer 1940s Oldsmobile Straight-8 engine A Straight-8 is a straight engine with eight cylinders. ... 1933 Bugatti Type 59 Grand Prix racer from the Ralph Lauren collection Wikimedia Commons has more media related to: Category:1933 Bugatti Type 59 Grand Prix The Type 51 series succeeded the famous Type 35 as Bugattis premier racing car for the 1930s. ... Grand Prix motor racing has its roots in organised automobile racing that began in France as far back as 1894. ... Fiat S.p. ... Peugeot is a major French car brand, part of PSA Peugeot Citroën. ... Alfa Romeo is an Italian automobile manufacturing company, founded as Darracq Italiana by Cavaliere Ugo Stella, an aristocrat from Milan in partnership with the French automobile firm of Alexandre Darracq. ... A.L.F.A. 40/60 GP or GP was an early racing car prototype (fully running) made by company today called Alfa Romeo. ... The Alfa Romeo 6C name was used on road, race and sports cars made between 1925–1954 by Alfa Romeo. ... A 1957 Maserati 200SI at the Scarsdale Concours Maserati Birdcage 1959 Maserati 5000 GT Coupe Maserati Sebring This article is about the automobile manufacturer. ... For other uses, see Bugatti (disambiguation). ... 1933 Bugatti Type 59 Grand Prix racer from the Ralph Lauren collection Wikimedia Commons has more media related to: Category:1933 Bugatti Type 59 Grand Prix The Type 51 series succeeded the famous Type 35 as Bugattis premier racing car for the 1930s. ... Audi AG is a German automobile manufacturer with headquarters in Ingolstadt, Bavaria, and has been an almost wholly owned (99. ... For other uses, see Ferrari (disambiguation). ...

When DOHC technology was introduced in mainstream vehicles, it was common for the technology to be heavily advertised. While the technology was used at first in limited production and sports cars, the Fiat group is historically credited as the first car company to use a belt driven DOHC engine across their complete product line, composed of coupes, sedans, convertibles and station wagons, in the mid-1960s.

See also

• Valvetrain
• Pushrod
• Cam-in-block
• Camless

A traditional reciprocating internal combustion engine uses valves to to control air and fuel flow into and out of the cylinders, facilitating combustion. ... A pushrod engine or overhead valve (OHV) engine is a type of piston engine that places the camshaft below the pistons (usually beside and slightly above the crankshaft in a straight engine or directly above the crankshaft in the V of a V engine) and uses pushrods or rods to... It has been suggested that this article or section be merged with pushrod engine. ... Most piston engines today employ a camshaft to operate poppet valves. ...

External links

• OHV, SOHC, DOHC engine animated diagrams