Overhead valve engine

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Components of a traditional OHV engine valvetrain Pushrod2.PNG
Components of a traditional OHV engine valvetrain

An overhead valve (OHV) engine, 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.


Although an overhead camshaft (OHC) engine also has overhead valves, the common usage of the term "overhead valve engine" is limited to engines where the camshaft is located in the engine block. In these traditional OHV engines, the motion of the camshaft is transferred using pushrods (hence the term "pushrod engine") and rocker arms to operate the valves at the top of the engine. However, some designs have the camshaft in the cylinder head but still sit below or alongside the valves (the Ford CVH and Opel CIH are good examples), so they can essentially be considered overhead valve designs.

Some early intake-over-exhaust engines used a hybrid design combining elements of both side-valves and overhead valves. [1]


1894 prototype overhead valve Diesel engine Experimental Diesel Engine.jpg
1894 prototype overhead valve Diesel engine
1904 patent for Buick overhead valve engine Valve-In-Head 1904 patent.jpg
1904 patent for Buick overhead valve engine


The first internal combustion engines were based on steam engines and therefore used slide valves. [2] This was the case for the first Otto engine, which was first successfully run in 1876. As internal combustion engines began to develop separately to steam engines, poppet valves became increasingly common.

Beginning with the 1885 Daimler Reitwagen, several cars and motorcycles used inlet valve(s) located in the cylinder head, however these valves were vacuum-actuated ("atmospheric") rather than driven by a camshaft as with typical OHV engines. The exhaust valve(s) were driven by a camshaft, but were located in the engine block as with side-valve engines.

The 1894 Diesel prototype engine used overhead poppet valves actuated by a camshaft, pushrods and rocker arms, [3] [4] therefore becoming the first OHV engines. In 1896, U.S. patent 563,140 was taken out by William F. Davis for an OHV engine with liquid coolant used to cool the cylinder head, [5] [6] but no working model was built.

Production OHV engines

In 1898, bicycle manufacturer Walter Lorenzo Marr in the United States built a motorised tricycle powered by a single-cylinder OHV engine. [7] Marr was hired by Buick (then named Buick Auto-Vim and Power Company) from 1899–1902, where the overhead valve engine design was further refined. [8] This engine employed pushrod-actuated rocker arms, which in turn opened poppet valves parallel to the pistons. Marr returned to Buick in 1904 (having built a small quantity of the Marr Auto-Car, with one of the first known engines to use an overhead camshaft design), the same year that Buick received a patent for an overhead valve engine design. In 1904, the world's first production OHV engine was released in the Buick Model B. The engine was a flat-twin design with two valves per cylinder. The engine was very successful for Buick, with the company selling 750 such cars in 1905, and the OHV engine has powered almost all Buick automobiles since then.

Several other manufacturers began to produce OHV engines, such as the 1906–1912 Wright Brothers Vertical 4-Cylinder Engine. [9] [10] In 1911, Chevrolet joined Buick in almost exclusive use of OHV engines. [11] However, side-valve engines remained commonplace until the mid-to-late 1960s, [12] when they began to be phased out for OHV engines.

Overhead camshaft engines

The first overhead camshaft (OHC) engine dates back to 1902, in the Marr; [13] however, use of this design was mostly limited to high-performance cars for many decades. OHC engines slowly became more common from the 1950s to the 1990s, and by the start of the 21st century, the majority of automotive engines (except for some North American V8 engines) used an OHC design. [14]

At the 1994 Indianapolis 500 motor race, Team Penske entered a car powered by the custom-built Mercedes-Benz 500I pushrod engine. Due to a loophole in the rules, the pushrod engine was allowed to use a larger displacement and higher boost pressure, significantly increasing its power output compared to the OHC engines used by other teams. Team Penske qualified in pole position and won the race by a large margin.

In the early 21st century, several pushrod V8 engines from General Motors and Chrysler used variable displacement to reduce fuel consumption and exhaust emissions. In 2008, the first production pushrod engine to use variable valve timing was introduced in the Dodge Viper (fourth generation). [15]


V8 engine (with intake manifold removed), showing the camshaft, pushrods, and rockers Pushrod engine.jpg
V8 engine (with intake manifold removed), showing the camshaft, pushrods, and rockers

OHV engines have several advantages compared with OHC engines:

Compared with OHC engines, OHV engines have the following disadvantages:

Related Research Articles

<span class="mw-page-title-main">Sleeve valve</span> Valve mechanism for piston engines

The sleeve valve is a type of valve mechanism for piston engines, distinct from the usual poppet valve. Sleeve valve engines saw use in a number of pre–World War II luxury cars and in the United States in the Willys-Knight car and light truck. They subsequently fell from use due to advances in poppet-valve technology, including sodium cooling, and the Knight system double sleeve engine's tendency to burn a lot of lubricating oil or to seize due to lack of it. The Scottish Argyll company used its own, much simpler and more efficient, single sleeve system (Burt-McCollum) in its cars, a system which, after extensive development, saw substantial use in British aircraft engines of the 1940s, such as the Napier Sabre, Bristol Hercules, Centaurus, and the promising but never mass-produced Rolls-Royce Crecy, only to be supplanted by the jet engines.

<span class="mw-page-title-main">Poppet valve</span> Type of valve

A poppet valve is a valve typically used to control the timing and quantity of gas or vapor flow into or out of an engine, but with many other applications.

<span class="mw-page-title-main">Camshaft</span> Mechanical component that converts rotational motion to reciprocal motion

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.

<span class="mw-page-title-main">Cylinder head</span> Component of an internal combustion engine

In an internal combustion engine, the cylinder head sits above the cylinders and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas in more modern overhead valve and overhead camshaft engines, the cylinder head is a more complicated block often containing inlet and exhaust passages, coolant passages, valves, camshafts, spark plugs and fuel injectors. Most straight engines have a single cylinder head shared by all of the cylinders and most V engines have two cylinder heads.

<span class="mw-page-title-main">Hemispherical combustion chamber</span> Combustion chamber with a domed cylinder head

A hemispherical combustion chamber is a type of combustion chamber in a reciprocating internal combustion engine with a domed cylinder head notionally in the approximate shape of a hemisphere. An engine featuring this type of hemispherical chamber is known as a hemi engine.

<span class="mw-page-title-main">Crossflow cylinder head</span>

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.

<span class="mw-page-title-main">Desmodromic valve</span> Reciprocating engine valve actuation mechanism

A desmodromic valve is a reciprocating engine poppet valve that is positively closed by a cam and leverage system, rather than by a more conventional spring.

<span class="mw-page-title-main">Chrysler LA engine</span> Reciprocating internal combustion engine

The LA engines are a family of pushrod OHV small-block 90° V-configured gasoline engines built by Chrysler Corporation. They were factory-installed in passenger vehicles, trucks and vans, commercial vehicles, marine and industrial applications from 1964 through 2003. Their combustion chambers are wedge-shaped, rather than polyspherical, as in the predecessor A engine, or hemispherical in the Hemi. LA engines have the same 4.46 in (113 mm) bore spacing as the A engines.

<span class="mw-page-title-main">Overhead camshaft engine</span> Valvetrain configuration

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.

<span class="mw-page-title-main">Multi-valve</span> Type of car engine

In automotive engineering a multi-valve or multivalve engine is one where each cylinder has more than two valves. A multi-valve engine has better breathing and may be able to operate at higher revolutions per minute (RPM) than a two-valve engine, delivering more power.

<span class="mw-page-title-main">Flathead engine</span> A type of four-stroke engine

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.

<span class="mw-page-title-main">Tappet</span> Internal combustion engine part

A tappet is a valve train component which converts rotating motion into linear motion in activating a valve. It is most commonly found in internal combustion engines, which converts the rotating motion of the camshaft into linear motion of intake and exhaust valves, either directly or indirectly.

<span class="mw-page-title-main">Rocker arm</span> Oscillating lever in engine

In the context of an internal combustion engine, a rocker arm is a valvetrain component that typically transfers the motion of a pushrod to the corresponding intake/exhaust valve.

<span class="mw-page-title-main">Valvetrain</span> Mechanical system in an internal combustion engine

A valvetrain or valve train 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 gasses out of the combustion chamber once combustion is completed.

<span class="mw-page-title-main">Wasserboxer</span> Reciprocating internal combustion engine

The Volkswagen wasserboxer is a four cylinder horizontally opposed pushrod overhead-valve (OHV) petrol engine developed by Volkswagen. The engine is water-cooled, and takes its name from the German: "wasserboxer" ("Water-boxer"); with "boxer" being another term for horizontally opposed engines. It was available in two displacements – either a 1.9-litre or a 2.1-litre; the 2.1-litre being a longer stroke version of the 1.9-litre, both variants sharing the same cylinder bore. This engine was unique to the Volkswagen Type 2 (T3), having never been used in any other vehicle. Volkswagen contracted Oettinger to develop a six-cylinder version of this engine. Volkswagen decided not to use it, but Oettinger sold a Volkswagen Type 2 (T3) equipped with this engine.

A hydraulic tappet, also known as a hydraulic valve lifter or hydraulic lash adjuster, is a device for maintaining zero valve clearance in an internal combustion engine. Conventional solid valve lifters require regular adjusting to maintain a small clearance between the valve and its rocker or cam follower. This space prevents the parts from binding as they expand with the engine's heat, but can also lead to noisy operation and increased wear as the parts rattle against one another until they reach operating temperature. The hydraulic lifter was designed to compensate for this small tolerance, allowing the valve train to operate with zero clearance—leading to quieter operation, longer engine life, and eliminating the need for periodic adjustment of valve clearance.

<span class="mw-page-title-main">IOE engine</span> Type of combustion engines

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.

<span class="mw-page-title-main">Walter Lorenzo Marr</span>

Walter Lorenzo Marr (1865-1941) was an automotive pioneer and engineer who worked with David Dunbar Buick perfecting the first Buick production automobiles. He worked with Mr. Buick a number of times around the turn of the century, building Buick's first two one-off vehicles. He was the Buick Motor Company's first chief engineer from 1904 through 1918, staying on as consulting engineer until 1923. He was also the founder of the Marr Auto Car Company in 1903 which produced the Marr Auto Car. The Marr Auto Car was one of the world's first automobiles with an overhead camshaft (OHC) engine.

<span class="mw-page-title-main">4 VD 14,5/12-1 SRW</span> Reciprocating internal combustion engine

The 4 VD 14,5/12-1 SRW is an inline four-cylinder diesel engine produced by the VEB IFA Motorenwerke Nordhausen from 1967 to 1990. The engine was one of the standard modular engines for agricultural and industrial use in the Comecon-countries. Approximately one million units were made.

<span class="mw-page-title-main">Mercedes-Benz OM 138</span> Reciprocating internal combustion engine

The Mercedes-Benz OM 138 is a diesel engine manufactured by Daimler-Benz. In total, 5,719 units were produced between 1935 and 1940. It was the first diesel engine especially developed and made for a passenger car. The first vehicle powered by the OM 138 was the Mercedes-Benz W 138. The light Mercedes-Benz trucks L 1100 and L 1500 as well as the bus O 1500 were also offered with the OM 138 as an alternative to the standard Otto engine.


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