Valves are used in most piston engine cylinder heads to open and close, thereby sealing off the intake and exhaust ports in the cylinder head combustion chamber/s. The valve is usually a flat disk of metal with a long rod known as the valve stem which is attached to one side, also referred to as 'poppet valves'.

For certain applications the valve stem and disk are made of different steel alloys, or the valve stems were made be hollow and filled with sodium to improve heat transport and transfer. This process had drawbacks, one being that the stem had to be a larger diameter to accommodate the sodium. Today most engine designs have moved away from sodium filled valves and found alternatives because of the thicker stem which disrupts airflow.

Because the valve stem extends into lubrication in the cam chamber, it must be sealed against blow-by to prevent cylinder gases from escaping into the crankcase, even though the stem to valve clearance is very small. The valve stem is required to be sealed by a rubber seal called the ‘valve stem seal’ which ensures that excessive amounts of oil are not drawn in from the crankcase on the induction stroke and that exhaust gas does not enter the crankcase on the exhaust stroke.

The camshaft is used to push down on the valve by means of a cam follower which opens the valve accordingly, with a valve spring (sometimes two valve springs), which returns the valve back to its closed seated position when the valve is not being depressed by the cam lobe ‘toe’. The shape and position of the cam determines the valve lift and when and how quickly or slowly the valve is opened. The cams are normally placed on a fixed camshaft which is then geared to the crankshaft, running at half crankshaft speed in a four stroke engine.

In most flathead engine designs the camshaft remained relatively near the crankshaft, and the valves were operated through pushrods and rocker arms. This led to significant energy losses in the engine, but was simpler, especially in a V engine where one camshaft can actuate the valves for both cylinder banks; for this reason, pushrod engine designs persisted longer in these configurations than others.

More modern designs have the camshaft on top of the cylinder head, pushing directly on the valve stem, again through cam followers, also known as tappets, a system known as overhead camshaft. If there is just one camshaft, the engine is referred to as a single overhead cam or SOHC engine. Often there are two camshafts, one for the intake valves and one for the exhaust valves, thereby creating the dual overhead cam.

Aluminum cylinder heads require hardened steel valve seat inserts with unleaded fuel. Modern fuels are absent from lead which coated the seats thus cushioning the valve and seat, in effect lubricating the metal with lead. Valve seats are now commonly made of improved alloys such as satellite which have generally made this problem disappear completely and made leaded fuels unnecessary.

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The internal combustion engine comprises of many parts and the most important part is the cylinder head which is positioned above the cylinders on top of the cylinder block. The head seals off the top of the piston cylinders, forming the combustion chambers. The cylinder head and block are joined together with a seal called the cylinder head gasket. The cylinder head also provides spaces for the passage ways that feed air and fuel and air/fuel mixtures to the cylinders aswell as passages that allow the burnt exhaust gasses to escape called inlet and exhaust ports.

The cylinder head ports allow the fuel/air mixture to travel into the combustion chamber through the inlet valves from the intake manifold and for burnt exhaust gasses to travel out from the combustion chambers exhaust valves to the exhaust manifold and exhaust. In a water cooled engine, the cylinder head also contains ducts and passages for water/coolant to circulate thus cooling the cylinder head and engine block which also has water passages, and therefore cooling the engine in general.

In the overhead valve (OHV) design, the cylinder head contains the poppet valves and the spark plugs, along with tracts or ports for the inlet and exhaust gases. The operation of the valves is initiated by the engine's camshaft, which is sited within the cylinder block, and its moment of operation is transmitted to the valves pushrods, and then rocker arms mounted on a rocker shaft, the rocker arms and shaft also being located within the cylinder head.

In the OHC design, the cylinder head contains the valves, spark plugs and inlet/exhaust ports just like the OHV engine, but the camshaft is now also contained within the cylinder head. The camshaft may be seated centrally between each offset row of inlet and exhaust valves, and still also utilizing rocker arms (but without any pushrods), or the camshaft may be seated directly above the valves eliminating the rocker arms and utilizing 'cam bucket' tappets also called ‘cam followers’.

Almost all in-line straight engines use a single cylinder head that serves all the cylinders. A ‘V’ engine has two cylinder heads, one for each cylinder bank of the 'V' form. For a few compact 'narrow angle' V engines, such as the Volkswagen VR6, the angle between the cylinder banks is so narrow that it uses a single head spanning the two banks. A flat engine where the angle between the cylinder banks is 180° has two heads. Most radial engines have one head for each cylinder.

Some engines, particularly medium and large capacity diesel engines mostly have individual cylinder heads for each cylinder. This reduces repair costs as a single failed head on a single cylinder can be changed instead of a larger, much more expensive unit fitting all the cylinders. The design of the cylinder head is key to the performance and efficiency of the internal combustion engine, as the shape of the combustion chamber to piston, inlet port passages and exhaust ports.

A camshaft is a shaft comprising of multiple cam lobes which operate the valves either directly or through a linkage of pushrods and rockers found inside an internal combustion engine. Direct operation involves a simpler mechanism and leads to fewer failures, but requires the camshaft to be positioned at the top of the cylinders. In modern petrol engines the over head cam system is where the camshaft is positioned on top of the cylinder head.

Since the valves control the flow of the air/fuel mixture intake and exhaust gases, they must be opened and closed at the appropriate time during the stroke of the piston. For this reason, the camshaft is connected to the crankshaft either directly, via a gear mechanism, or indirectly via a belt or chain. In some designs the camshaft also drives the distributor and the oil and fuel pumps.

The timing of the camshaft can be advanced to produce better low RPM and torque, or retarded for better high RPM power. Either of these moves the overall power produced by the engine up or down the RPM scale respectively.

Duration is the number of crankshaft degrees of engine rotation during which the valve is off the seat. As a generality, greater duration results in more horsepower. The RPM at which peak horsepower occurs is typically increased as duration increases at the expense of lower rpm efficiency (torque).

A secondary effect of increase duration is increasing overlap, which is the number of crankshaft degrees during which both intake and exhaust valves are off their seats. It is overlap which most affects idle quality, as with the ‘blow-through’ of the intake charge which occurs during overlap reduces engine efficiency, and is greatest during low RPM operation. In reality, increasing a camshaft's duration typically increases the overlap.

The further the valve rises from its seat the more airflow can be achieved which is beneficial. Greater lift has some limitations. Firstly, the lift is limited by the increased proximity of the valve head to the piston crown and secondly greater effort is required to move the valve's springs to higher state of compression.

Higher lift allows accurate timing of airflow; although even by allowing a larger volume of air to pass in the relatively larger opening, the brevity of the typical duration with a higher lift cam results in less airflow than with a cam with lower lift but more duration. On forced induction motors this higher lift could yield better results than longer duration, particularly on the intake side. Notably though, higher lift has more potential problems than increased duration, in particular as valve train rpm rises which can result in more inefficient running or loss of torque.

Cams that have too high a resultant valve lift, and at high rpm, can result in what is called ‘valve bounce’. This could also be as a result of a very steep rise of the lobe and short duration, where the valve is effectively shot off the end of the cam rather than have the valve follow the cams’ profile.

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The crankshaft is the part of an engine which translates reciprocating linear piston motion into rotation. The crankshaft has a linear axis about which it rotates, typically with several bearing journals riding on replaceable bearings with the main crank bearings housed in the crankcases main bearing caps. As the crankshaft undergoes a great deal of sideways load from each cylinder in a multi cylinder engine, it must be supported by several such main bearing web housings. High performance engines often have more main bearings and extra bolts for added insurance.

The distance the axis of the crank throws from the axis of the crankshaft determines the stroke of the crankshaft which means distance the piston travels from bottom dead centre (BDC) to top dead centre (TDC), thus determining engine displacement. A common way to increase the low speed torque of an engine is to increase the stroke, often referred to as ‘stroking’. In compensation, it improves the low speed operation of the engine, as the longer intake stroke through smaller valves results in greater turbulence and mixing of the intake charge.

The engine design or configuration and number of pistons in relation to each other and the crankshaft itself leads to a straight in-line, V-configuration or flat-engine design. Production V8 engines use four crank throws spaced 90° apart, high-performance V8 engines often use a ‘flat’ crankshaft with throws spaced 180° apart. For certain engines it is necessary to provide counterweights for the reciprocating mass of each piston and connecting rod to improve the engine balance. These counterweights are cast as part of the crankshaft and while counter weights add a considerable amount of weight to the crankshaft, it provides a smoother running engine and allows higher revolutions to be attained.

Crankshafts can be forged from a steel bar usually through forging or cast in steel. Vehicle manufacturers favor the use of forged crankshafts due to their lighter weight, more compact dimensions and reliability. With forged crankshafts, vanadium microalloyed steels are mostly used as these steels can be air cooled after reaching high strengths without additional heat treatment. Carbon steels are also used, but these require additional heat treatment to reach the desired properties. Cast iron crankshafts are today mostly found in standard production engines where the loads are lower.

Crankshafts can also be machined out of a billet. These crankshafts tend to be very expensive due to the large amount of material removal which needs to be done by using lathes and milling machines, the high material cost and the additional heat treatment required. However, since no expensive tooling is required, this production method allows small production runs of crankshafts to be made without high costs.

Most production crankshafts use induction hardened bearing surfaces since that method gives good results with low costs. It also allows the crankshaft to be reground without having to redo the hardening. Nitridization is is a hardening process used by crank builders that it can be done at low temperatures, it produces a very hard surface.

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