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 earlier 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.

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 one of 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 the first known engine 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.

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 late 1940s, when they began to be phased out for OHV engines.

Overhead camshaft engines

The first overhead camshaft (OHC) engine dates back to 1902, [12] 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.

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). [13]


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">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 an engine.

<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.

<span class="mw-page-title-main">Hemispherical combustion chamber</span>

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> Motor vehicle engine

The LA engines are a family of pushrod OHV small block 90° V-configured gasoline engines built by Chrysler Corporation. It was factory-installed in passenger vehicles, trucks and vans, commercial vehicles, marine and industrial applications from 1964 through 1991 (318) & 1992 (360). The combustion chambers are wedge-shaped, rather than the polyspherical combustion chambers in the predecessor A engine or the hemispherical combustion chambers in the Chrysler Hemi engine. LA engines have the same 4.46 in (113 mm) bore spacing as the A engines. LA engines were made at Chrysler's Mound Road Engine plant in Detroit, Michigan, as well as plants in Canada and Mexico. The "LA" stands for "Light A", as the 1956 - 1967 "A" engine it was closely based on and shares many parts with was nearly 50 pounds heavier. The "LA" and "A" production overlapped from 1964 - 1966 in the US and through 1967 in export vehicles when the "A" 318 engine was phased out. Willem Weertman, who later became Chief Engineer – Engine Design and Development, was in charge of the conversion. The basic design of the LA engine would go unchanged through the development of the "Magnum" upgrade (1992-1993) and into the 2000s with changes to enhance power and efficiency.

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

An overhead camshaft (OHC) engine is a piston engine where 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">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 most commonly a component in an internal combustion engine which converts the rotating motion of the camshaft into linear motion of the 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> Motor vehicle 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 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">BMW M328</span> Motor vehicle engine

The BMW M328 is an overhead valve straight-six petrol engine which was produced from 1936 to 1940. It was a high-performance development of the BMW M78 engine that was produced alongside the M78.

<span class="mw-page-title-main">4 VD 14,5/12-1 SRW</span> Motor vehicle 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> Motor vehicle 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.

<span class="mw-page-title-main">Otto A.G.O. 80/100 hp</span>

The Otto A.G.O. 80/100 hp aircraft engine from 1911 was a four-cylinder, water cooled inline engine built by the German Gustav Otto Flugmaschinenwerke.


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