![De Dion-Bouton engine (Rankin Kennedy, Modern Engines, Vol III)](https://upload.wikimedia.org/wikipedia/commons/1/1a/De_Dion-Bouton_engine_%28Rankin_Kennedy%2C_Modern_Engines%2C_Vol_III%29.jpg)
A ''monobloc'' or ''en bloc'' engine is an internal-combustion piston engine some of whose major components (such as
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 ...
,
cylinder block, or
crankcase
In a piston engine, the crankcase is the housing that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block.
Two-stroke engines typically use a crankcase-compression design, resulting in the fuel/a ...
) are formed, usually by
casting
Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...
, as a single integral unit, rather than being assembled later. This has the advantages of improving mechanical stiffness, and improving the reliability of the sealing between them.
''Monobloc'' techniques date back to the beginnings of the
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 ...
. Use of the term has changed over time, usually to address the most pressing mechanical problem affecting the engines of its day. There have been three distinct uses of the technique:
*
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 ...
and cylinder
*
Cylinder block
* Cylinder block and
crankcase
In a piston engine, the crankcase is the housing that surrounds the crankshaft. In most modern engines, the crankcase is integrated into the engine block.
Two-stroke engines typically use a crankcase-compression design, resulting in the fuel/a ...
In most cases, any use of the term describes single-unit construction that is opposed to the more common contemporary practice. Where the monobloc technique has later become the norm, the specific term fell from favour. It is now usual practice to use monobloc cylinders and crankcases, but a monobloc head (for a water-cooled inline engine at least) would be regarded as peculiar and obsolescent.
Cylinder head
![Air-cooled monobloc cylinder, section (Manual of Driving and Maintenance)](https://upload.wikimedia.org/wikipedia/commons/f/fa/Air-cooled_monobloc_cylinder%2C_section_%28Manual_of_Driving_and_Maintenance%29.jpg)
The
head gasket
In an internal combustion engine, a head gasket provides the seal between the engine block and cylinder head(s).
Its purpose is to seal the combustion gases within the cylinders and to avoid coolant or engine oil leaking into the cylinders. Leak ...
is the most highly stressed static seal in an engine, and was a source of considerable trouble in early years. The monobloc cylinder head forms both cylinder and head in one unit, thus averting the need for a seal.
Along with head gasket failure, one of the least reliable parts of the early petrol engine was the exhaust valve, which tended to fail by overheating. A monobloc head could provide good water cooling, thus reduced valve wear, as it could extend the water jacket uninterrupted around both head and cylinder. Engines with gaskets required a metal-to-metal contact face here, disrupting water flow.
The drawback to the monobloc head is that access to the inside of the combustion chamber (the upper volume of the cylinder) is difficult. Access through the cylinder bore is restricted for machining the valve seats, or for inserting angled valves. An even more serious restriction is de-coking and re-grinding valve seats, a regular task on older engines. Rather than removing the cylinder head from above, the mechanic must remove pistons, connecting rods and the crankshaft from beneath.
One solution to this for
side-valve engine
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 with its poppet valves contained within the Cam-in-block, engine block, instead of in the cyli ...
s was to place a screwed plug directly above each valve, and to access the valves through this (illustrated). The tapered threads of the screwed plug provided a reliable seal. For low-powered engines this was a popular solution for some years, but it was difficult to cool this plug, as the water jacket didn't extend into the plug. As performance increased, it also became important to have better combustion chamber designs with less "dead space". One solution was to place the
spark plug
A spark plug (sometimes, in British English, a sparking plug, and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air ...
in the centre of this plug, which at least made use of the space. This placed the spark plug further from the combustion chamber, leading to long flame paths and slower ignition.
During
World War I
World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
, development of the internal combustion engine greatly progressed. After the war, as civilian car production resumed, the monobloc cylinder head was required less frequently. Only high-performance cars such as the
Leyland Eight of 1920 persisted with it.
Bentley
Bentley Motors Limited is a British designer, manufacturer and marketer of luxury cars and SUVs. Headquartered in Crewe, England, the company was founded as Bentley Motors Limited by W. O. Bentley (1888–1971) in 1919 in Cricklewood, North ...
and
Bugatti
Automobiles Ettore Bugatti was a German then French manufacturer of high-performance automobiles. The company was founded in 1909 in the then-German city of Molsheim, Alsace, by the Italian-born industrial designer Ettore Bugatti. The cars w ...
were other racing marques who notably adhered to them, through the 1920s and into the 1930s, most famously being used in the purpose-built American
Offenhauser
The Offenhauser Racing Engine, or Offy, is a racing engine design that dominated American open wheel racing for more than 50 years and is still popular among vintage sprint and midget car racers.
History
The Offenhauser engine, familiarly ...
straight-four racing engines, first designed and built in the 1930s.
Aircraft engines at this time were beginning to use high
supercharging
In an internal combustion engine, a supercharger compresses the intake gas, forcing more air into the engine in order to produce more power for a given displacement.
The current categorisation is that a supercharger is a form of forced induc ...
pressures, increasing the stress on their head gaskets. Engines such as the
Rolls-Royce Buzzard
The Rolls-Royce Buzzard was a British piston aero engine of capacity that produced about . Designed and built by Rolls-Royce Limited it is a V12 engine of Bore and Stroke. Only 100 were made. A further development was the Rolls-Royce R e ...
used monobloc heads for reliability.
The last engines to make widespread use of monobloc cylinder heads were large air-cooled aircraft
radial engine
The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders "radiate" outward from a central crankcase like the spokes of a wheel. It resembles a stylized star when viewed from the front, and is ca ...
s, such as the
Wasp Major
The Pratt & Whitney R-4360 Wasp Major is an American 28-cylinder four-row radial engine, radial reciprocating engine, piston aircraft engine designed and built during World War II. First run in 1944, at , it is the largest-displacement aviation ...
. These have individual cylinder barrels, so access is less restricted than on an inline engine with a monobloc crankcase and cylinders, as most modern engines are. As they have high specific power and require great reliability, the advantages of the monobloc remained attractive.
General aviation engines such as
Franklin
Franklin may refer to:
People
* Franklin (given name)
* Franklin (surname)
* Franklin (class), a member of a historical English social class
Places Australia
* Franklin, Tasmania, a township
* Division of Franklin, federal electoral d ...
,
Continental
Continental may refer to:
Places
* Continent, the major landmasses of Earth
* Continental, Arizona, a small community in Pima County, Arizona, US
* Continental, Ohio, a small town in Putnam County, US
Arts and entertainment
* ''Continental'' ( ...
, and
Lycoming are still manufactured new and continue to use monobloc individual cylinders, although Franklin uses a removable sleeve. A combination of materials are used in their construction, such as steel for the cylinder barrels and aluminum alloys for the cylinder heads to save weight. Common rebuilding techniques include
chrome plating
Chrome plating (less commonly chromium plating) is a technique of electroplating a thin layer of chromium onto a metal object. A chrome-plated item is called ''chrome''. The chromed layer can be decorative, provide corrosion resistance, ease ...
the inside of the cylinder barrels in a "cracked" finish that mimics the "
cross-hatched" finish normally created by typical cylinder honing. Older engines operated on
unleaded automotive gasoline as allowed by
supplemental type certificates approved by the
FAA
The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...
may require more frequent machining replacement of valves and seats. Special tools are used to maintain valve seats in these cylinders.
Non-destructive testing
Nondestructive testing (NDT) is any of a wide group of analysis techniques used in science and technology industry to evaluate the properties of a material, component or system without causing damage.
The terms nondestructive examination (NDE), n ...
should be performed to look for flaws that may have arisen during extreme use, engine damage from sudden propeller stoppage or extended engine operation at every overhaul or rebuild.
Historically the difficulties of machining, and maintaining a monobloc cylinder head were and continue to be a severe drawback. As head gaskets became able to handle greater heat and pressure, the technique went out of use. It is almost unknown today, but has found a few niche uses, as the technique of monobloc cylinder heads was adopted by the Japanese
model engine
A model engine is a small internal combustion engine typically used to power a radio-controlled aircraft, radio-controlled car, radio-controlled boat, free flight, control line aircraft, or ground-running tether car model.
Because of the s ...
manufacture
Saito Seisakushofor their
glow fueled and spark ignition model four-stroke engines for
RC aircraft propulsion needs.
Monobloc cylinders also continue to be used on small 2 stroke-cycle engines for power equipment used to maintain lawns and gardens, such as string trimmers, tillers and leaf blowers.
Cylinder block
Casting
Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...
technology at the dawn of the internal combustion engine could reliably cast either large castings, or castings with complex internal
core
Core or cores may refer to:
Science and technology
* Core (anatomy), everything except the appendages
* Core (manufacturing), used in casting and molding
* Core (optical fiber), the signal-carrying portion of an optical fiber
* Core, the centra ...
s to allow for water jackets, but not both simultaneously. Most early engines, particularly those with more than four cylinders, had their cylinders cast as pairs or triplets of cylinders, then bolted to a single crankcase.
As casting techniques improved, the entire cylinder block of four, six or even eight cylinders could be cast as one. This was a simpler construction, thus less expensive to manufacture,
and the communal water jacket permitted closer spacing between cylinders. This also improved the mechanical stiffness of the engine, against bending and the increasingly important torsional twist, as cylinder numbers and engine lengths increased.
In the context of aircraft engines, the non-monobloc precursor to monobloc cylinders was a construction where the cylinders (or at least their liners) were cast as individuals, and the outer water jacket was applied later from copper or steel sheet. This complex construction was expensive, but lightweight, and so it was only widely used for aircraft.
V engine
A V engine, sometimes called a Vee engine, is a common configuration for internal combustion engines. It consists of two cylinder banks—usually with the same number of cylinders in each bank—connected to a common crankshaft. These cylinder ...
s remained with a separate block casting for each
bank
A bank is a financial institution that accepts deposits from the public and creates a demand deposit while simultaneously making loans. Lending activities can be directly performed by the bank or indirectly through capital markets.
Because ...
. The complex ducting required for
inlet manifold
In automotive engineering, an inlet manifold or intake manifold (in American English) is the part of an engine that supplies the fuel/air mixture to the cylinders. The word '' manifold'' comes from the Old English word ''manigfeald'' (from th ...
s between the banks were too complicated to cast otherwise. For economy, a few engines, such as the
V12 Pierce-Arrow, were designed to use identical castings for each bank, left and right.
[ Ludvigsen, V12 Engine, p. 120] Some rare engines, such as the
Lancia
Lancia () is an Italian car manufacturer and a subsidiary of FCA Italy S.p.A., which is currently a Stellantis division. The present legal entity of Lancia was formed in January 2007 when its corporate parent reorganised its businesses, but it ...
22½° narrow-angle V12 of 1919, did use a single block casting for both banks.
[ Ludvigsen, V12 Engine, p. 50-53]
Modern cylinders, except for air-cooled engines and some
V engine
A V engine, sometimes called a Vee engine, is a common configuration for internal combustion engines. It consists of two cylinder banks—usually with the same number of cylinders in each bank—connected to a common crankshaft. These cylinder ...
s, are now universally cast as a single cylinder block, and modern heads are nearly always separate components.
Crankcase
![Stripped Rover V8 engine](https://upload.wikimedia.org/wikipedia/commons/c/cd/Stripped_Rover_V8_engine.JPG)
As casting improved and cylinder blocks became a monobloc, it also became possible to cast both cylinders and crankcase as one unit. The main reason for this was to improve stiffness of the engine construction, reducing vibration and permitting higher speeds.
Most engines, except some V engines, are now a monobloc of crankcase and cylinder block.
Modern engines - Combined block, head and crankcase
Light-duty consumer-grade
Honda GC-family
small engine
A small engine is the general term for a wide range of small-displacement, low-powered internal combustion engines used to power lawn mowers, generators, concrete mixers and many other machines that require independent power sources. These eng ...
s use a monobloc design where the cylinder head, block, and half the crankcase share the same casting, termed 'uniblock' by Honda.
[ Includes sectioned drawings] One reason for this, apart from cost, is to produce an overall lower engine height. Being an air-cooled
OHC design, this is possible thanks to current aluminum casting techniques and lack of complex hollow spaces for liquid cooling. The valves are vertical, so as to permit assembly in this confined space. On the other hand, performing basic repairs becomes so time-consuming that the engine can be considered disposable. Commercial-duty
Honda GX-family engines (and their many popular
knock-offs) have a more conventional design of a single crankcase and cylinder casting, with a separate cylinder head.
Honda produces many other head-block-crankcase monoblocs under a variety of different names, such as the GXV-series. They may all be externally identified by a gasket which bisects the crankcase on an approximately 45° angle.
References
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Engine technology
Piston engine configurations