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A flathead engine, also known as a sidevalve engine''American Rodder'', 6/94, pp.45 & 93. or valve-in-block engine is an
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...
with its
poppet valve A poppet valve (also called mushroom valve) is a valve typically used to control the timing and quantity of gas or vapor flow into an engine. It consists of a hole or open-ended chamber, usually round or oval in cross-section, and a plug, usual ...
s contained within the
engine block In an internal combustion engine, the engine block is the structure which contains the cylinders and other components. In an early automotive engine, the engine block consisted of just the cylinder block, to which a separate crankcase was atta ...
, instead of in the
cylinder head In an internal combustion engine, the cylinder head (often abbreviated to simply "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 ov ...
, as in an
overhead valve engine 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 bel ...
. Flatheads were widely used internationally by automobile manufacturers from the late 1890s until the mid-1950s but were replaced by more efficient overhead valve and overhead camshaft engines. They are currently experiencing a revival in low-revving aero-engines such as the
D-Motor D-Motor is a Belgian aircraft engine manufacturer based in Deerlijk. The company specializes in the design and manufacture of aircraft engines for homebuilt and ultralight aircraft.Bayerl, Robby; Martin Berkemeier; et al: ''World Directory o ...
.


The side-valve design

The valve gear comprises a camshaft sited low in the cylinder block which operates the
poppet In folk magic and witchcraft, a poppet (also known as poppit, moppet, mommet or pippy) is a doll made to represent a person, for casting spells on that person or to aid that person through magic. They are occasionally found lodged in chimneys ...
valves A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fitting ...
via
tappet 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. An earlier use of the term was for part of the valve gear ...
s and short pushrods (or sometimes with no pushrods at all). The flathead system obviates the need for further
valvetrain 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 (or air alone for direct-injected engines) ...
components such as lengthy pushrods, rocker arms, overhead valves or
overhead camshaft 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 c ...
s. The sidevalves are typically adjacent, sited on one side of the cylinder(s), though some flatheads employ the less common "crossflow" "T-head" variant. In a T-head engine, the exhaust gases leave on the opposite side of the cylinder from the intake valve. The sidevalve engine's combustion chamber is not above the piston (as in an OHV (overhead valve) engine) but to the side, above the valves. The spark plug may be sited over the piston (as in an OHV engine) or above the valves; but aircraft designs with two plugs per cylinder may use either or both positions. "Pop-up pistons" may be used with compatible heads to increase compression ratio and improve the combustion chamber's shape to prevent knocking. "Pop-up" pistons are so called because, at
top dead centre In a reciprocating engine, the dead centre is the position of a piston in which it is either farthest from, or nearest to, the crankshaft. The former is known as Top Dead Centre (TDC) while the latter is known as Bottom Dead Centre (BDC). ...
, they protrude above the top of the cylinder block.


Advantages

The advantages of a sidevalve engine include: simplicity, reliability, low part count, low cost, low weight, compactness, responsive low-speed power, low mechanical engine noise, and insensitivity to low-octane fuel. The absence of a complicated valvetrain allows a compact engine that is cheap to manufacture, since the cylinder head may be little more than a simple metal casting. These advantages explain why side valve engines were used for
passenger cars A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded as ...
for many years, while
OHV 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 bel ...
designs came to be specified only for high-performance applications such as
aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
,
luxury car A luxury car is a car that provides increased levels of comfort, equipment, amenities, quality, performance, and associated status compared to moderately priced cars. The term is subjective and reflects both the qualities of the car and the ...
s,
sports car A sports car is a car designed with an emphasis on dynamic performance, such as handling, acceleration, top speed, the thrill of driving and racing capability. Sports cars originated in Europe in the early 1900s and are currently produced by ...
s, and some
motorcycles A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruising ...
. At top dead centre, the piston gets very close to the flat portion of the cylinder head above, and the resultant squish
turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
produces excellent fuel/air mixing. A feature of the sidevalve design (particularly beneficial for an aero-engine) is that if a valve should seize in its guide and remain partially open, the piston would not be damaged, and the engine would continue operating safely on its other cylinders.


Disadvantages

The main disadvantages of a sidevalve engine are poor gas flow, poor combustion chamber shape, and low compression ratio, all of which result in a low-revving engine with low power output and low efficiency.H. Kremser (author): Der Aufbau schnellaufender Verbrennungskraftmaschinen, in Hans List (ed): Die Verbrennungskraftmaschine, volume 11, Springer, Wien 1942, , p. 50 Because sidevalve engines do not burn the fuel efficiently, they suffer from high hydrocarbon emissions. Sidevalve engines can only be used for engines operating on the Otto principle. The combustion chamber shape is unsuitable for Diesel engines.Anton Pischinger (author): Die Steuerung der Verbrennungskraftmaschinen, in Hans List (ed): Die Verbrennungskraftmaschine, volume 9, Springer, Wien 1948, , p. 14 In a sidevalve engine, intake and exhaust gases follow a circuitous route, with low volumetric efficiency, or "poor breathing", not least because the exhaust gases interfere with the incoming charge. Because the exhaust follows a lengthy path to leave the engine, there is a tendency for the engine to overheat. (Note: this is true for V-type flathead engines but less of an issue for inline engines which typically have the intake and exhaust ports on the same side of the engine block.) Although a sidevalve engine can safely operate at high speed, its
volumetric efficiency Volumetric efficiency (VE) in internal combustion engine engineering is defined as the ratio of the mass density of the air-fuel mixture drawn into the cylinder at atmospheric pressure (during the intake stroke) to the mass density of the same volu ...
swiftly deteriorates, so that high power outputs are not feasible at speed. High volumetric efficiency was less important for early cars because their engines rarely sustained extended high speeds, but designers seeking higher power outputs had to abandon the sidevalve. A compromise used by the
Willys Jeep The Willys MB and the Ford GPW, both formally called the U.S. Army Truck, -ton, 4×4, Command Reconnaissance, commonly known as the Willys Jeep, Jeep, or jeep, and sometimes referred to by its supply catalogue designation G503,According to i ...
,
Rover Rover may refer to: People * Constance Rover (1910–2005), English historian * Jolanda de Rover (born 1963), Dutch swimmer * Rover Thomas (c. 1920–1998), Indigenous Australian artist Places * Rover, Arkansas, US * Rover, Missouri, US ...
,
Landrover Land Rover is a British brand of predominantly four-wheel drive, off-road capable vehicles, owned by multinational car manufacturer Jaguar Land Rover (JLR), since 2008 a subsidiary of India's Tata Motors. JLR currently builds Land Rovers ...
, and
Rolls-Royce Rolls-Royce (always hyphenated) may refer to: * Rolls-Royce Limited, a British manufacturer of cars and later aero engines, founded in 1906, now defunct Automobiles * Rolls-Royce Motor Cars, the current car manufacturing company incorporated in ...
in the 1950s was the "F-head" (or "intake-over-exhaust" valving), which has one sidevalve and one overhead valve per cylinder. The flathead's elongated combustion chamber is prone to
preignition In spark ignition internal combustion engines, knocking (also knock, detonation, spark knock, pinging or pinking) occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignite ...
(or "knocking") if compression ratio is increased, but improvements such as laser ignition or microwave enhanced ignition might help prevent knocking. Turbulence grooves may increase swirl inside the combustion chamber, thus increasing torque, especially at low rpm. Better mixing of the fuel/air charge improves combustion and helps to prevent knocking. An advance in flathead technology resulted from experimentation in the 1920s by
Sir Harry Ricardo Sir Harry Ralph Ricardo (26 January 1885 – 18 May 1974) was an English engineer who was one of the foremost engine designers and researchers in the early years of the development of the internal combustion engine. Among his many other works, ...
, who improved their efficiency after studying the gas-flow characteristics of sidevalve engines. The difficulty in designing a high-compression-ratio flathead means that most tend to be spark-ignition designs, and flathead diesels are virtually unknown.


History and applications

The sidevalve arrangement was especially common in the United States and used for motor vehicle engines, even for engines with high specific power output. Sidevalve designs are still common for many
small Small may refer to: Science and technology * SMALL, an ALGOL-like programming language * Small (anatomy), the lumbar region of the back * ''Small'' (journal), a nano-science publication * <small>, an HTML element that defines smaller text ...
single-cylinder A single-cylinder engine, sometimes called a thumper, is a piston engine with one cylinder. This engine is often used for motorcycles, motor scooters, go-karts, all-terrain vehicles, radio-controlled vehicles, portable tools and garden machinery ( ...
or twin-cylinder engines, such as
lawnmower A lawn mower (also known as a mower, grass cutter or lawnmower) is a device utilizing one or more revolving blades (or a reel) to cut a grass surface to an even height. The height of the cut grass may be fixed by the design of the mower, but g ...
s, rotavators,
two-wheel tractor Two-wheel tractor or walking tractor (french: motoculteur, russian: мотоблок (motoblok), german: Einachsschlepper) are generic terms understood in the US and in parts of Europe to represent a single-axle tractor, which is a tractor with ...
s and other basic farm machinery.


Flathead cars

Multicylinder flathead engines were used for cars such as the
Ford Model T The Ford Model T is an automobile that was produced by Ford Motor Company from October 1, 1908, to May 26, 1927. It is generally regarded as the first affordable automobile, which made car travel available to middle-class Americans. The relati ...
and Ford Model A, the Ford flathead V8 engine and the
Ford Sidevalve engine The Ford Sidevalve is a side valve (flathead engine) from the British arm of the Ford Motor Company, often also referred to as the "English Sidevalve". The engine had its origins in the 1930s Ford Model Y, and was made in two sizes, or "8 HP", a ...
.
Cadillac The Cadillac Motor Car Division () is a division of the American automobile manufacturer General Motors (GM) that designs and builds luxury vehicles. Its major markets are the United States, Canada, and China. Cadillac models are distributed i ...
produced V-16 flathead engines for their Series 90 luxury cars from 1938–1940. After
WWII World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, flathead designs began to be superseded by OHV (overhead valve) designs. Flatheads were no longer common in
cars A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded as t ...
, but they continued in more rudimentary vehicles such as off-road military Jeeps. In US custom car and hot rod circles, restored examples of early Ford flathead V8s are still seen.


Flathead aero-engines

The simplicity, lightness, compactness and reliability might seem ideal for an aero-engine, but because of their low efficiency, early flathead engines were deemed unsuitable. Two notable exceptions were the American
Aeronca E-107 The Aeronca E-107 was one of the first low-cost reliable engines of the post-World War I era. Design and development The E-107A was a production aviation flathead engine designed to replace a Morehouse engine on the first prototype of the Aer ...
opposed twin aero engine of 1930 and the
Continental A40 The Continental A40 engine is a carbureted four-cylinder, horizontally opposed, air-cooled aircraft engine that was developed especially for use in light aircraft by Continental Motors. It was produced between 1931 and 1941. Design and develop ...
flat four of 1931, which became one of the most popular light aircraft engines of the 1930s. Two modern flatheads are the Belgian
D-Motor D-Motor is a Belgian aircraft engine manufacturer based in Deerlijk. The company specializes in the design and manufacture of aircraft engines for homebuilt and ultralight aircraft.Bayerl, Robby; Martin Berkemeier; et al: ''World Directory o ...
flat-four A flat-four engine, also known as a horizontally opposed-four engine, is a four-cylinder piston engine with two banks of cylinders lying on opposite sides of a common crankshaft. The most common type of flat-four engine is the boxer-four engine, ...
s and
flat-six A flat-six engine, also known as a horizontally opposed-six, is a six-cylinder piston engine with three cylinders on each side of a central crankshaft. The most common type of flat-six engine is the boxer-six engine, where each pair of opposed cy ...
es. These are extremely oversquare and compact aero-engines with direct drive to a propeller.Tacke, Willi; Marino Boric; et al: ''World Directory of Light Aviation 2015-16'', pages 256-257. Flying Pages Europe SARL, 2015.


Flathead motorcycles

Flathead designs have been used on a number of early pre-war motorcycles, in particular US V-twins such as
Harley-Davidson Harley-Davidson, Inc. (H-D, or simply Harley) is an American motorcycle manufacturer headquartered in Milwaukee, Wisconsin, United States. Founded in 1903, it is one of two major American motorcycle manufacturers to survive the Great Depressi ...
and
Indian Indian or Indians may refer to: Peoples South Asia * Indian people, people of Indian nationality, or people who have an Indian ancestor ** Non-resident Indian, a citizen of India who has temporarily emigrated to another country * South Asia ...
, some British singles, BMW
flat twin A flat-twin engine is a two-cylinder internal combustion engine with the cylinders on opposite sides of the crankshaft. The most common type of flat-twin engine is the boxer-twin engine, where both pistons move inwards and outwards at the same ti ...
s and Russian copies thereof.For example, some Dnepr and Ural used flathead designs that BMW had licensed to the Soviets. The
Cleveland Motorcycle Manufacturing Company The Cleveland Motorcycle Manufacturing Company, sometimes called Cleveland Motorcycle, was a motorcycle manufacturer in Cleveland, Ohio, from 1902 to 1905 and again from 1915 to 1929. Two-stroke singles The first Cleveland of 1915 had a Engin ...
produced a T-head four-cylinder in-line motorcycle engine in the 1920s. Image:1915 Cadillac Model 51 V8 4stroke engine photo2.JPG, 1915 Cadillac flathead engine block Image:flathead.jpg, Harley-Davidson flathead Image:Indian Chief Black Hawk 80 cubic inch 1950.jpg, Indian Chief Black Hawk Image:BMW motorbike R 12 (aka).jpg, BMW R12 Image:Cleveland Model 4-45 1927.jpg, Cleveland Model 4-45


See also

* Heron Head


Notes


External links


Ford Flathead EngineHarley-Davidson K-model motorcycles
{{DEFAULTSORT:Flathead Engine Cam-in-block valvetrain configurations Engine technology Engine valvetrain configurations Harley-Davidson engines Motorcycle engines Piston engines