Flathead engine
Encyclopedia
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
with valves
Poppet valve
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. The shaft guides the plug portion by sliding through a valve guide...
placed in the engine block beside the piston
Piston
A piston is a component of reciprocating engines, reciprocating pumps, gas compressors and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from...
, instead of in the cylinder head
Cylinder head
In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...
, as in an overhead valve
Overhead valve
An overhead valve engine, also informally called pushrod engine or I-head engine, is a type of piston engine that places the camshaft within the cylinder block , and uses pushrods or rods to actuate rocker arms above the cylinder...
engine. As the cylinder cross-section has the shape of an upside-down L, this leads to other names: L-block, or L-head.
The sidevalve's poppet valves are usually sited on one side of the cylinder(s)). A recess in the cylinder head
Cylinder head
In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...
creates a corridor connecting the valves and the combustion chamber. The valve gear comprises a camshaft which operates the valves via simple tappets, without any further valvetrain
Valvetrain
Valvetrain is an all-encompassing term used to describe the mechanisms and parts which control the operation of the valves. A traditional reciprocating internal combustion engine uses valves to control air and fuel flow into and out of the cylinders, facilitating combustion.-Layout:Valvetrain: The...
paraphernalia (such as pushrods, rocker arms, overhead valve
Overhead valve
An overhead valve engine, also informally called pushrod engine or I-head engine, is a type of piston engine that places the camshaft within the cylinder block , and uses pushrods or rods to actuate rocker arms above the cylinder...
s or overhead camshaft
Overhead camshaft
Overhead cam valvetrain configurations place the engine camshaft within the cylinder heads, above the combustion chambers, and drive the valves or lifters in a more direct manner compared to overhead valves and pushrods...
s). The sidevalve arrangement was common in early engine designs, but it has since fallen from favor.
Advantages
The main advantages of a sidevalve engine are simplicity, reliability, cheapness, compactness, responsive low-speed power, ability to use low-octane fuel, and safety from damage at high rpm.An important benefit of the a sidevalve design is that, if a valve should drop, only limited damage would occur, and the engine might continue to operate with a broken valve. (By comparison, an OHV or OHC engine can suffer piston damage and catastrophic engine failure when a valve drops.) The design is intrinsically not an interference engine design. The absence of a complicated valvetrain allows a compact engine that is cheap to manufacture. In particular, the cylinder head may be little more than a simple metal casting, and the simple valve gear engenders reliability.
Because intake and exhaust gases pass through the same corridor between the block and head, and because the light valve gear allows the valves to open and close quickly, flatheads are designed with minimal valve overlap (where both intake and exhaust valves are simultaneously open). This gives better low rpm performance than with OHV or OHC engines which use valve overlap to gain high rpm. Although a sidevalve engine can safely operate at high speed, its volumetric efficiency swiftly deteriorates, so that a high power outputs are not feasible at speed.
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 power output.The maximum compression ratio
Compression ratio
The 'compression ratio' of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity...
is low at about 7:1, reducing efficiency but permitting the vehicle to run on low-octane fuel.
The sidevalve configuration makes intake and exhaust gases follow a circuitous route, with low volumetric efficiency, or "poor breathing". High volumetric efficiency was less important for early cars because their engines rarely sustained extended high speeds; but designers seeking higher outputs had to abandon the sidevalve. A compromise used by Willys (Jeep)
Willys MB
The Willys MB US Army Jeep and the Ford GPW, were manufactured from 1941 to 1945. These small four-wheel drive utility vehicles are considered the iconic World War II Jeep, and inspired many similar light utility vehicles. Over the years, the World War II Jeep later evolved into the "CJ" civilian...
, Rover and Rolls-Royce
Rolls-Royce Limited
Rolls-Royce Limited was a renowned British car and, from 1914 on, aero-engine manufacturing company founded by Charles Stewart Rolls and Henry Royce on 15 March 1906 as the result of a partnership formed in 1904....
in the1950s was the F-head (aka intake-over-exhaust configuration), in which there is one side valve and one overhead valve per cylinder.
An advance in flathead technology resulted from experimentation in the 1920s by Sir Harry Ricardo, who improved their efficiency after studying the gas-flow characteristics of sidevalve engines . The Ricardo head moved the exhaust valve farther from the center of the cylinder than the intake valve (whereas they had previously been equidistant). Ricardo observed how the form of the inlet and exhaust tracts affected gas flow and turbulence both in the inlet stream and within the combustion chamber.
Because the exhaust follows a complicated path to leave the engine, there is a tendency for the engine to overheat. In a T-block (aka T-head), a sidevalve engine has a crossflow configuration, so exhaust gases leave on the opposite side of the cylinder from the intake valve. American LaFrance
American LaFrance
American LaFrance is an emergency and vocational vehicle manufacturer, currently based in Summerville, South Carolina. Focusing primarily on emergency apparatus fire engines and fire aerial including ambulance and rescue vehicles.-History:...
powered their fire engines with T-head engines from the 1920s to the 1950s. The Cleveland Motorcycle Company produced a T-head four-cylinder in-line motorcycle engine in the 1920s; and early Stutz
Stutz Motor Company
The Stutz Motor Company was a producer of luxury cars based in Indianapolis, Indiana, USA. Production began in 1911 and continued through 1935. The marque reappeared in 1968 under the aegis of Stutz Motor Car of America, Inc., and with a newly defined modern retro-look. Although the company is...
engines were T heads.
History and applications
Although flathead in-line 4 and 6 cylinder engines were frequently used for automobiles, tractors, and other products, the best known flathead automotive engine is the early 20th century Ford V-8Ford Flathead engine
The Ford flathead V8 was a V8 engine of the flathead type, designed by the Ford Motor Company and built by Ford and various licensees...
, which has both sets of valves (intake and exhaust) located on the inside of the "Vee," and which are all operated by a single camshaft
Camshaft
A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...
located above the crankshaft
Crankshaft
The crankshaft, sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation...
. Other common configurations included in-line ("straight") eights and a V 12 Lincoln
Lincoln (automobile)
Lincoln is an American luxury vehicle brand of the Ford Motor Company. Lincoln vehicles are sold mostly in North America.-History:The company was founded in August 1915 by Henry M. Leland, one of the founders of Cadillac . During World War I, he left Cadillac which was sold to General Motors...
version of the Ford V 8.
Due to cooling and efficiency problems, flathead engines fell out of favor in "high power" applications, such as aircraft engine
Aircraft engine
An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...
s, prior to World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
. However they lived on for some time in the automotive world and were used on the Jeep
Jeep
Jeep is an automobile marque of Chrysler . The first Willys Jeeps were produced in 1941 with the first civilian models in 1945, making it the oldest off-road vehicle and sport utility vehicle brand. It inspired a number of other light utility vehicles, such as the Land Rover which is the second...
for instance. Flatheads are no longer in common use for automobile
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
s (except in some rodding
Hot rod
Hot rods are typically American cars with large engines modified for linear speed. The origin of the term "hot rod" is unclear. One explanation is that the term is a contraction of "hot roadster," meaning a roadster that was modified for speed. Another possible origin includes modifications to or...
and customizing
Custom car
A custom car is a passenger vehicle that has been modified in either of the following two ways. First, a custom car may be altered to improve its performance, often by altering or replacing the engine and transmission. Second, a custom car may be a personal "styling" statement, making the car look...
circles), although they are still used for some small-engine applications like lawnmowers. Because of their design, the size of valves and the compression ratio
Compression ratio
The 'compression ratio' of an internal-combustion engine or external combustion engine is a value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity...
are limited, which in turn reduces available power and economy.
A new arrival is the Belgian D-Motor LF26
D-Motor LF26
-See also:...
, a compact 2.5 litre flat-four aero-engine that has direct drive to a propeller, without any reduction gearbox. Dispensing with the complexity of an ohv valvetrain
Valvetrain
Valvetrain is an all-encompassing term used to describe the mechanisms and parts which control the operation of the valves. A traditional reciprocating internal combustion engine uses valves to control air and fuel flow into and out of the cylinders, facilitating combustion.-Layout:Valvetrain: The...
, the engine gives peak power of 80bhp at only 2800rpm. The resulting simplicity, lightness, compactness and reliability are ideal in an aero-engine. D-Motor is developing a 120 bhp 6-cylinder version.
Harley-Davidson motorcycle flathead engines
The flathead engine saw service in Harley-DavidsonHarley-Davidson
Harley-Davidson , often abbreviated H-D or Harley, is an American motorcycle manufacturer. Founded in Milwaukee, Wisconsin, during the first decade of the 20th century, it was one of two major American motorcycle manufacturers to survive the Great Depression...
motorcycle
Motorcycle
A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...
s beginning with the "Sport Model" opposed twin produced from 1919 to 1923, and continuing in 1924 with single cylinder export-model 21 cubic inch and 30.5 cubic inch singles and continued in the Servi-Cars until 1973. In the domestic U.S. market, the 45 cubic inch DL model (1929 to 1931) and its technical descendant, the RL model (1932 to 1936), started Harley's side valve tradition in the 45 cubic inch displacement class. The DL and RL models featured a total loss oiling system and were succeeded in 1937 by the WL 45, which had recirculating oil lubrication. The WL went on to serve in WWII as the U.S. and Canadian Army's primary two-wheeled mount and subsequently as a civilian middleweight through 1952. The engine continued virtually unchanged with various G-based designations in the three wheeled "Servi-Car" until production ceased in 1973.
In 1952, the K series flatheads was introduced, selling in parallel with the W series (which was discontinued after 1952), designed to compete with British sporting motorcycles of the time, as the American motorcycle Association allowed the 750 cc sidevalves to compete against 500 cc overhead-valve bikes. The K models featured a unit construction engine and transmission case, right side foot shift and left side foot brake, and evolved from 45 cubic inch (1952 to 1953) to 55 cubic inches by a 0.75 inches (19.1 mm) increase in stroke length (1954 to 1956) over its five year retail market run. The K series was replaced by the overhead valve Sportster series in the retail market in 1957. However, racing versions of the 750 cc K model, designated KR, continued to be produced in very limited numbers for some time after, winning both roadraces and dirt track events against overhead valve bikes limited to 500 cc through 1969, when the American Motorcycle Association finally decided to change the rules and make the venerable flatheads uncompetitive. The K racers were replaced first by the iron-head XR 750cc overhead valve engine, and two years later by the alloy-head XR, which continues in service in flat track racing to this day.
In 1930, the 74 cubic inch VL flathead replaced the JD Big Twin, which had featured intake-over-exhaust (IoE) valve configuration. The VL had a single downtube frame and total loss oiling, culminating in an 80 cubic inch version (VLH) in 1935. In 1937, that engine was redesigned to include a recirculating lubrication system, and designated the model U, and it went into the same frame and running gear configuration as the model E Knucklehead, which had originated in 1936. The U continued to be produced in varying configurations as a 74& cubic inch U & UL (1937 to 1948), and 80 cubic inch UH & ULH engine (1937 to 1941). By that time, the first year of the aluminum-head Panhead, it had been thoroughly superseded and outsold in the marketplace by the superior performance of the overhead valve model Big Twins.
Popular Culture
The reason that the overdrive of the Hot Rod LincolnHot Rod Lincoln
"Hot Rod Lincoln" was recorded in 1955, as an answer song to "Hot Rod Race", a 1951 hit for Arkie Shibley and his Mountain Dew Boys. Hot Rod Race tells the story of a late-model Ford and Mercury who end up racing along the highway, neither driver gaining an advantage, and staying "neck and neck"...
"just won't stall" is probably that it is a flathead V 12. (Flatheads in general, tend to have good low speed performance because of the lack of valve overlap).