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. [1] Leaks in the head gasket can cause poor engine running and/or overheating.
Within a water-cooled internal combustion engine, there are three fluids which travel between the engine block and the cylinder head:
Correct operation of the engine requires that each of these circuits do not leak or lose pressure at the junction of the engine block and the cylinder head. The head gasket is the seal that prevents these leaks and pressure losses.
A leak in the head gasket - often called a "blown head gasket" - can result in a leak of coolant, the combustion gasses, or both.
Blue smoke from the exhaust suggests that excess oil is entering the combustion chambers (although there are other possible causes than a head gasket leak). White smoke from the exhaust suggests that coolant is entering the combustion chamber.
Head gasket leaks are classified as either external or internal. External leaks are visible as oil or coolant on the outside of the engine (typically underneath). Internal leaks are when the fluids enter another circuit and may result in changes to the coolant or oil. The former may be the presence of foam (caused by hydrocarbons) in the coolant expansion tank. Coolant leaking into the oil system may result in a mayonnaise, or milkshake-like, substance in the oil, often to be seen on the dipstick, or oil filler cap. However, the presence of this substance is not conclusive proof of head gasket failure, since oil could mix with the coolant via other routes. Likewise, it is entirely possible for a head gasket to fail in such a way that oil never comes in contact with coolant. Therefore it is not possible to conclusively determine the head gasket condition by inspecting the oil.
If coolant enters a cylinder, the burning of the air/fuel mixture is compromised, reducing the engine's performance and often causing steam (white smoke) to be visible from the exhaust. [4] This steam can damage the catalytic converter. If a very large amount of coolant leaks into the cylinders, then the engine can suffer from hydrolock, which can cause extensive engine damage.
When the combustion gasses leak out of a cylinder, this causes a loss of compression, leading to power reduction or rough running. If the combustion gases are leaking into the cooling system, this reduces the effectiveness of the cooling system and can cause the engine to overheat. In other occurrences the gases can leak into small spaces between the gasket and either the cylinder head or engine block traps those gases, and then released when the engine is turned off. These gases then escape into the coolant and create air pockets. Sometimes these air pockets can get trapped in the engine's coolant thermostat, causing it to stay closed and cause further overheating, thereby creating more voids between the gasket and the engine. Other times these air pockets can also cause the engine to expel coolant into the overflow or expansion tank, thereby reducing the amount of coolant available for cooling.
Common test methods for head gasket leaks are a compression test (using a pressure gauge), a leak-down test or a chemical test that identifies hydrocarbons in the coolant fluid. [5]
The cost of the replacement component (i.e. the head gasket itself) is usually relatively low, however there are significant labor costs involved in the replacement process. [6] This is because the process of removing and replacing the cylinder head is a time-consuming task.
Engine knocking (detonation) can be caused by poor quality fuel, an engine fault or if inappropriate fuel and/or ignition settings are trialled/chosen while engine tuning is taking place. If the detonation is severe, the cylinder pressure can increase to eight times above normal pressures,[ citation needed ] which can cause the cylinder head to lift away from the engine block, disrupting the seal between the two. Most gaskets used in standard production engines can be critically damaged by severe detonation.
A poppet valve is a valve typically used to control the timing and quantity of petrol (gas) or vapour flow into or out of an engine, but with many other applications.
In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide (NOx) emissions reduction technique used in petrol/gasoline, diesel engines and some hydrogen engines. EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. The exhaust gas displaces atmospheric air and reduces O2 in the combustion chamber. Reducing the amount of oxygen reduces the amount of fuel that can burn in the cylinder thereby reducing peak in-cylinder temperatures. The actual amount of recirculated exhaust gas varies with the engine operating parameters.
In spark-ignition internal combustion engines, knocking occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but when one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front. The fuel–air charge is meant to be ignited by the spark plug only, and at a precise point in the piston's stroke. Knock occurs when the peak of the combustion process no longer occurs at the optimum moment for the four-stroke cycle. The shock wave creates the characteristic metallic "pinging" sound, and cylinder pressure increases dramatically. Effects of engine knocking range from inconsequential to completely destructive.
In a piston engine, the cylinder head sits above the cylinders, forming the roof of the combustion chamber. In sidevalve engines the head is a simple plate of metal containing the spark plugs and possibly heat dissaption fins. In more modern overhead valve and overhead camshaft engines, the head is a more complicated metal block that also contains the inlet and exhaust passages, and often coolant passages, Valvetrain components, and fuel injectors.
Top Fuel is a type of drag racing whose dragsters are the quickest accelerating racing cars in the world and the fastest sanctioned category of drag racing, with the fastest competitors reaching speeds of 338 miles per hour (544.0 km/h) and finishing the 1,000 foot (304.8 m) runs in 3.62 seconds.
Pre-ignition in a spark-ignition engine is a technically different phenomenon from engine knocking, and describes the event wherein the air/fuel mixture in the cylinder ignites before the spark plug fires. Pre-ignition is initiated by an ignition source other than the spark, such as hot spots in the combustion chamber, a spark plug that runs too hot for the application, or carbonaceous deposits in the combustion chamber heated to incandescence by previous engine combustion events.
A combustion chamber is part of an internal combustion engine in which the fuel/air mix is burned. For steam engines, the term has also been used for an extension of the firebox which is used to allow a more complete combustion process.
Internal combustion engine cooling uses either air or liquid to remove the waste heat from an internal combustion engine. For small or special purpose engines, cooling using air from the atmosphere makes for a lightweight and relatively simple system. Watercraft can use water directly from the surrounding environment to cool their engines. For water-cooled engines on aircraft and surface vehicles, waste heat is transferred from a closed loop of water pumped through the engine to the surrounding atmosphere by a radiator.
In a reciprocating engine, the cylinder is the space in which a piston travels.
In automotive engineering, an exhaust manifold collects the exhaust gases from multiple cylinders into one pipe. The word manifold comes from the Old English word manigfeald and refers to the folding together of multiple inputs and outputs.
Power Stroke, also known as Powerstroke or PowerStroke, is the name used by a family of diesel engines for trucks produced by Ford Motor Company and Navistar International for Ford products since 1994. Along with its use in the Ford F-Series, applications include the Ford E-Series, Ford Excursion, and Ford LCF commercial truck. The name was also used for a diesel engine used in South American production of the Ford Ranger.
Regenerative cooling, in the context of rocket engine design, is a configuration in which some or all of the propellant is passed through tubes, channels, or in a jacket around the combustion chamber or nozzle to cool the engine. This is effective because the propellants are often cryogenic. The heated propellant is then fed into a special gas-generator or injected directly into the main combustion chamber.
Hydrolock is an abnormal condition of any device which is designed to compress a gas by mechanically restraining it; most commonly the reciprocating internal combustion engine, the case this article refers to unless otherwise noted. Hydrolock occurs when a volume of liquid greater than the volume of the cylinder at its minimum enters the cylinder. Since liquids are nearly incompressible the piston cannot complete its travel; either the engine must stop rotating or a mechanical failure must occur.
The Bourke engine was an attempt by Russell Bourke, in the 1920s, to improve the two-stroke internal combustion engine. Despite finishing his design and building several working engines, the onset of World War II, lack of test results, and the poor health of his wife compounded to prevent his engine from ever coming successfully to market. The main claimed virtues of the design are that it has only two moving parts, is lightweight, has two power pulses per revolution, and does not need oil mixed into the fuel.
A crankcase ventilation system (CVS) removes unwanted gases from the crankcase of an internal combustion engine. The system usually consists of a tube, a one-way valve and a vacuum source.
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.
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Radiators are heat exchangers used for cooling internal combustion engines, mainly in automobiles but also in piston-engined aircraft, railway locomotives, motorcycles, stationary generating plants or any similar use of such an engine.
An internal combustion engine is a heat engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combustion engine, the expansion of the high-temperature and high-pressure gases produced by combustion applies direct force to some component of the engine. The force is typically applied to pistons, turbine blades, a rotor, or a nozzle. This force moves the component over a distance, transforming chemical energy into kinetic energy which is used to propel, move or power whatever the engine is attached to.
Since exposure to asbestos is now recognized as being a health hazard [...] the manufacture of non-asbestos cylinder head gaskets has now become established.