A valve job is the colloquial term for resurfacing the mating surfaces of the poppet valves and their respective valve seats that control the intake and exhaust of the air/fuel mixture in four stroke internal combustion engine, replacing valve oil seals, replacing any deficient valve springs, and otherwise bringing the components of a cylinder head up to manufacturer’s spec. [1] A resurfacing of the head’s meeting surface with the engine block to true it is often done at the same time if a head has been removed from the engine.
Some reasons that may induce the need for a valve job in a modern passenger car include: excessive RPM, high mileage, overheating, material failure, corrosion, and foreign object damage (FOD).
In the earliest automotive engines, the valves needed to be removed and the sealing surfaces sanded, ground or lapped multiple times during the life of a typical engine. As the decades passed, however, engines ran cleaner and the addition of tetraethyllead in gasoline meant that such maintenance became less frequent. Today, valve jobs are rarely done on passenger cars for the purpose of maintenance, although they are still quite common with high-performance cars.
A valve job is best done with grinding stones and either electric or pneumatic tools. Lapping compound and a lapping tool may be used, and is more economical for home auto repair, however lapping will only provide limited results and will not be effective on a valve or seat with anything more than very light wear or damage.
Modern engines have cylinder heads made of either iron or aluminum. Iron cylinder heads most often have integral iron valve seats. These seats are the softest and most susceptible to wear among modern engines. Much softer yet aluminum cylinder heads, however, have replaceable pressed-in hardened steel valve seats. These are significantly stronger than the integral seats of an iron head, and can be relatively easily swapped out as needed. If an integral iron seat needs to be replaced, the seat must be milled to allow the insertion of a new seat. The new seat is then installed with application of a high-strength metal glue/adhesive. Once installed, the seat is ground to the correct angle and width.
Valves and seats must have the same angle to mate properly. That angle is usually 45 degrees, but 30 degrees can be found in many modern applications. The mating angle is often accompanied by top and bottom angle cuts that are 15 degrees from each side of the mating angle (e.g. for a 45 degree seat, the top and bottom angles would be 30 and 60 degrees respectively). This method increases air-flow, which gives mild horsepower, response, and efficiency improvements.
Valves are inspected for damage such as cracking, pitting, channeling, and burning that will prevent proper operation and could lead to catastrophic failure. Pitting is permissible in small amounts, but should not be present on the valve face, margin, or stem. Channeling is a result of uneven heating of a valve (typically from improper seating during operation), and is evident by heat discoloration in an oval shape on the bottom of the valve and often visible at the base of the valve stem. Channeling that continues will lead to a burnt valve (the melting away of a portion of the valve). If an engine has been subjected to excessive RPM or sudden stoppage, all valves should be inspected for straightness, as a bent valve or valve stem will quickly lead to failure, and often damage other parts such as pistons, cylinder walls, other valves, valve guides, and valve-train components.
Some older cars have relatively soft valve seats that wear faster when operated without leaded fuel. These usually can be updated with hardened valve seats that resist wear, regardless of whether leaded or unleaded fuel is used.
A valve is a device or natural object that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically fittings, but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure. The word is derived from the Latin valva, the moving part of a door, in turn from volvere, to turn, roll.
The sleeve valve is a type of valve mechanism for piston engines, distinct from the usual poppet valve. Sleeve valve engines saw use in a number of pre–World War II luxury cars and in the United States in the Willys-Knight car and light truck. They subsequently fell from use due to advances in poppet-valve technology, including sodium cooling, and the Knight system double sleeve engine's tendency to burn a lot of lubricating oil or to seize due to lack of it. The Scottish Argyll company used its own, much simpler and more efficient, single sleeve system (Burt-McCollum) in its cars, a system which, after extensive development, saw substantial use in British aircraft engines of the 1940s, such as the Napier Sabre, Bristol Hercules, Centaurus, and the promising but never mass-produced Rolls-Royce Crecy, only to be supplanted by the jet engines.
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.
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.
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.
Engine tuning is the adjustment or modification of the internal combustion engine or Engine Control Unit (ECU) to yield optimal performance and increase the engine's power output, economy, or durability. These goals may be mutually exclusive; an engine may be de-tuned with respect to output power in exchange for better economy or longer engine life due to lessened stress on engine components.
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.
The Chevrolet Vega is a subcompact automobile that was manufactured and marketed by GM's Chevrolet division from 1970 to 1977. Available in two-door hatchback, notchback, wagon, and sedan delivery body styles, all models were powered by an inline four-cylinder engine designed specifically for the Vega, with a lightweight, aluminum alloy cylinder block. The Vega first went on sale in Chevrolet dealerships on September 10, 1970. Variants included the Cosworth Vega, a short-lived limited-production performance model, introduced in the spring of 1975.
In car tuning culture, an engine swap is the process of removing a car's original engine and replacing it with another. This may be a like-for-like replacement, or to install a non-factory specification engine. Typically, an engine swap is performed for performance, swapping-in a more powerful engine; however, an engine swap may also be performed for maintenance, where older engines may have a shortage of spare parts, and so a modern replacement may be more easily and cheaply maintained.
The Fiat Twin Cam is an advanced double overhead camshaft inline-four automobile engine produced from 1966 through 2000 as a Fiat/Lancia engine. Designed by ex Ferrari engineer Aurelio Lampredi, the engine was produced in a large number of displacements, ranging from 1.3 to 2.0 L and was used in Fiat, Lancia, Alfa Romeo, SEAT, FSO and Morgan cars. The Fiat Twin Cam engine has been widely used in motorsport and has been the most successful engine in the history of the World Rally Championship. Fiat and Lancia won a total of ten World Rally Championships for Manufacturers using engines based on the Lampredi Twin Cam engine. It was replaced by the Fiat "family B" Pratola Serra engine series.
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.
The valve seat in an internal combustion gasoline or diesel engine is the surface against which an intake or an exhaust valve rests during the portion of the engine operating cycle when that valve is closed. The valve seat is a critical component of an engine in that if it is improperly positioned, oriented, or formed during manufacture, valve leakage will occur which will adversely affect the engine compression ratio and therefore the engine efficiency, performance, exhaust emissions, and engine life.
Scavenging is the process of replacing the exhaust gas in a cylinder of an internal combustion engine with the fresh air/fuel mixture for the next cycle. If scavenging is incomplete, the remaining exhaust gases can cause improper combustion for the next cycle, leading to reduced power output.
Valve guides are cylindrical metal bushes, pressed or integrally cast into the cylinder head of most types of reciprocating engines, to support the poppet valves so that they may make proper contact with its valve seat. Along with a corresponding valve spring, they are one component of an engine’s valve train.
The VR5 engines are a family of petroleum fuelled Internal combustion engines developed by the Volkswagen Group and produced from 1997 to 2006. They are derived from the VR6 engine family, also developed by Volkswagen, but with one fewer cylinders. The VR5 is highly compact, thanks to the narrower angle of 15° and a displacement of 2,324 cc. The VR5 was the first production block to use five cylinders in a VR design with a 15-degree angle.
The Triumph Ricardo was a British single-cylinder motorcycle manufactured by the Triumph Engineering Co Ltd between 1921 and 1928. Named after engine designer Sir Harry Ricardo it featured an innovative four valve head design and was capable of over 70 mph, set three world speed records and won a gold medal in the 1923 International Six Day Trial.
A monobloc or en bloc engine is an internal-combustion piston engine some of whose major components are formed, usually by casting, 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.
The term power assembly refers to an Electro-Motive Diesel (EMD) engine sub-assembly designed to be "easily" removed and replaced in order to restore engine performance lost to wear or engine failure. Typical of heavy-duty internal combustion engines used in industrial applications, EMD engines are designed to allow the cylinder liners, pistons, piston rings and connecting rods to be replaced at overhaul without removing the entire engine assembly from its application location. This increases engine value, reduces downtime and allows the engine to be returned to true new engine performance. Other terms such as cylinder pack, liner pack, cylinder assembly and cylinder kit are used in the engine industry to describe similar assemblies. In the large-engine industry, the term "power assembly" has also become generic and is often used to refer to the assemblies used in non-EMD engines where "power pack" may be the preferred term, although both terms are functionally the same.
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.