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35-516: Compared with the M42, the M44 has roller rocker arms , a hot-wire MAF , displacement increased from 1.8 to 1.9 L (110 to 116 cu in) and other detail changes such as a grey cast iron crankshaft replacing the forged steel item from the previous M42. As per the final versions of the M42, the M44 has a dual length intake manifold ("DISA"). Peak power is the same as the M42, however mid-range power

70-402: A bearing at the contact point, to reduce wear and friction at the contact point. The most common use of a rocker arm is to transfer the motion of a pushrod in an overhead valve (OHV) internal combustion engine to the corresponding intake/exhaust valve. In an OHV engine the camshaft at the bottom of the engine pushes the pushrod upwards. The top of the pushrod presses upwards on one side of

105-434: A bent valve if it gets struck by the piston. The timing (phase angle) of the camshaft relative to the crankshaft can be adjusted to shift an engine's power band to a different RPM range. Advancing the camshaft (shifting it to ahead of the crankshaft timing) increases low RPM torque, while retarding the camshaft (shifting it to after the crankshaft) increases high RPM power. The required changes are relatively small, often in

140-441: A camshaft with the same duration rating that has been determined using different lift points (for example 0.006 or 0.002 inches) could be much different to a camshaft with a duration rated using lift points of 0.05 inches. A secondary effect of increased duration can be increased overlap , which determines the length of time that both the intake and exhaust valves are open. It is overlap which most affects idle quality, in as much as

175-405: 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 (to operate the intake and exhaust valves), mechanically controlled ignition systems and early electric motor speed controllers . Camshafts in piston engines are usually made from steel or cast iron, and the shape of the cams greatly affects

210-508: Is achieved through a bore of 85.0 mm (3.35 in) and a stroke of 83.5 mm (3.29 in). A compression ratio of 10.0:1 is used, along with the Bosch Motronic 5.2 engine management system. The crankshaft has an increased stroke from the M42's 81 mm (3.19 in) and is cast instead of forged. Also revised were the valve actuators which are of a roller pivoting arm type. Applications: With time this engine

245-415: Is increased significantly and peak torque is increased by 5 N⋅m (4 lb⋅ft) at 200 rpm lower. There was also a 70% reduction in valve train friction which contributed to the engine being more quiet and fuel efficient than its predecessor. The M44 has a cast iron block and aluminium cylinder head, as per its predecessor. The M44B19 has a displacement of 1,895 cc (115.6 cu in), which

280-647: The Uniflow steam engine , and the Gardner-Serpollet steam cars, which also included axially sliding the camshaft to achieve variable valve timing. Among the first cars to utilize engines with single overhead camshafts were the Maudslay, designed by Alexander Craig and introduced in 1902 and the Marr Auto Car designed by Michigan native Walter Lorenzo Marr in 1903. In piston engines ,

315-441: The valve guide . These allow higher engine speeds (RPMs) and higher loads, and were initially confined to high-performance and racing engines due to the considerable extra expense. Roller rockers can also be used in overhead cam engines (OHC). However, these generally have the roller at the point where the cam lobe contacts the rocker, rather than at the point where the rocker contacts the valve stem. Friction may be reduced at

350-488: The "blow-through" of the intake charge immediately back out through the exhaust valve which occurs during overlap reduces engine efficiency, and is greatest during low RPM operation. In general, increasing a camshaft's duration typically increases the overlap, unless the Lobe Separation Angle is increased to compensate. A lay person can readily spot a long duration camshaft by observing the broad surface of

385-408: The camshaft is used to operate the intake and exhaust valves . The camshaft consists of a cylindrical rod running the length of the cylinder bank with a number of cams (discs with protruding cam lobes ) along its length, one for each valve. As the cam rotates, the lobe presses on the valve (or an intermediate mechanism), thus pushing it open. Typically, a valve spring is used to push the valve in

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420-412: The camshaft operates the valve directly or via a short rocker arm. The valvetrain layout is defined according to the number of camshafts per cylinder bank. Therefore, a V6 engine with a total of four camshafts - two camshafts per cylinder bank - is usually referred to as a double overhead camshaft engine (although colloquially they are sometimes referred to as "quad-cam" engines). Accurate control of

455-429: The centreline of the exhaust lobes. A higher LSA reduces overlap, which improves idle quality and intake vacuum, however using a wider LSA to compensate for excessive duration can reduce power and torque outputs. In general, the optimal LSA for a given engine is related to the ratio of the cylinder volume to intake valve area. Camshafts are integral components of internal combustion engines, responsible for controlling

490-420: The crankshaft. In a four-stroke engine , the valves are opened only half as often, therefore the camshaft is geared to rotate at half the speed of the crankshaft. The camshaft's duration determines how long the intake/exhaust valve is open for, therefore it is a key factor in the amount of power that an engine produces. A longer duration can increase power at high engine speeds (RPM), however this can come with

525-416: The engine block near the bottom of the engine. Early flathead engines locate the valves in the block and the cam acts directly on those valves. In an overhead valve engine, which came later, the cam follower presses on a pushrod which transfers the motion to the top of the engine, where a rocker opens the intake/exhaust valve. Although largely replaced by SOHC and DOHC layouts in modern automobile engines,

560-517: The engine's characteristics. Trip hammers are one of the early uses of a form of cam to convert rotating motion, e.g. from a waterwheel, into the reciprocating motion of a hammer used in forging or to pound grain. Evidence for these exists back to the Han dynasty in China, and they were widespread by the medieval period. Once the rotative version of the steam engine was developed in the late 18th century,

595-469: The fulcrum is at the end rather than the middle, while the cam acts on the middle of the arm. The opposite end opens the valve. These types of rocker arms are particularly common on overhead camshaft engines, and are often used instead of direct tappets. This rocker arm configuration is employed in SOHC engines such as Ford 5.4 L 3v and Ford Zetec RoCam . The rocker ratio is the distance travelled by

630-427: The lobe where the cam pushes the valve open for a large number of degrees of crankshaft rotation. This will be visibly greater than the more pointed camshaft lobe bump that is observed on lower duration camshafts. The camshaft's lift determines the distance between the valve and the valve seat (i.e. how far open the valve is). The farther the valve rises from its seat the more airflow can be provided, thus increasing

665-448: The maximum amount of lift possible for a given engine. Firstly, increasing lift brings the valves closer to the piston, so excessive lift could cause the valves to get struck and damaged by the piston. Secondly, increased lift means a steeper camshaft profile is required, which increases the forces needed to open the valve. A related issue is valve float at high RPM, where the spring tension does not provide sufficient force to either keep

700-426: The older overhead valve layout is still used in many industrial engines, due to its smaller size and lower cost. As engine speeds increased through the 20th century, single overhead camshaft (SOHC) engines— where the camshaft is located within the cylinder head near the top of the engine— became increasingly common, followed by double overhead camshaft (DOHC) engines in more recent years. For OHC and DOHC engines,

735-598: The opening and closing of the engine's intake and exhaust valves. As the camshaft rotates, its lobes push against the valves, allowing the intake of air and fuel and the expulsion of exhaust gases. This synchronized process is crucial for optimizing engine performance, fuel efficiency, and emissions control. Without precisely engineered camshafts, the smooth and efficient operation of an engine would be compromised. The most common methods of valve actuation involve camshafts and valve springs, however alternate systems have occasionally been used on internal combustion engines: Before

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770-442: The operation of the valve gear was usually by an eccentric , which turned the rotation of the crankshaft into reciprocating motion of the valve gear, normally a slide valve . Camshafts more like those seen later in internal combustion engines were used in some steam engines, most commonly where high pressure steam (such as that generated from a flash steam boiler ), required the use of poppet valves, or piston valves. For examples see

805-416: The opposite direction, thus closing the valve once the cam rotates past the highest point of its lobe. Camshafts are made from metal and are usually solid, although hollow camshafts are sometimes used. The materials used for a camshaft are usually either: Many early internal combustion engines used a cam-in-block layout (such flathead , IOE or T-head layouts), whereby the camshaft is located within

840-468: The order of 5 degrees. Modern engines which have variable valve timing are often able to adjust the timing of the camshaft to suit the RPM of the engine at any given time. This avoids the above compromise required when choosing a fixed cam timing for use at both high and low RPM. The lobe separation angle (LSA, also called lobe centreline angle ) is the angle between the centreline of the intake lobes and

875-531: The past include a vertical shaft with bevel gears at each end (e.g. pre-World War I Peugeot and Mercedes Grand Prix Cars and the Kawasaki W800 motorcycle) or a triple eccentric with connecting rods (e.g. the Leyland Eight car). In a two-stroke engine that uses a camshaft, each valve is opened once for every rotation of the crankshaft; in these engines, the camshaft rotates at the same speed as

910-403: The past smaller positive ratios have been used, including a 1:1 (neutral ratio) in many engines prior to the 1950s, and ratios less than 1 (valve lift smaller than the cam lift) have also been used at times. Mass-produced car engines traditionally used a stamped steel construction for the rocker arms, due to the lower cost of production. Rocker arms contribute to the reciprocating weight of

945-425: The point of contact with the valve stem by a roller tip. A similar arrangement transfers the motion via another roller tip to a second rocker arm. This rotates about the rocker shaft, and transfers the motion via a tappet to the valve. Some OHC engines employ short rocker arms, also known as fingers, in which the cam lobe pushes down (rather than up) on the rocker arm to open the valve. On this type of rocker arm,

980-454: The position and speed of the camshaft is critically important in allowing the engine to operate correctly. The camshaft is usually driven either directly, via a toothed rubber "timing belt"' or via a steel roller "timing chain". Gears have also occasionally been used to drive the camshaft. In some designs the camshaft also drives the distributor , oil pump , fuel pump and occasionally the power steering pump. Alternative drive systems used in

1015-448: The power produced. Higher valve lift can have the same effect of increasing peak power as increased duration, without the downsides caused by increased valve overlap. Most overhead valve engines have a rocker ratio of greater than one, therefore the distance that the valve opens (the valve lift ) is greater than the distance from the peak of the camshaft's lobe to the base circle (the camshaft lift ). There are several factors which limit

1050-414: The rocker arm located at the top of the engine, which causes the rocker arm to pivot. This motion causes its other end to press downwards on the top of the valve , opening it. A roller rocker uses needle bearings (or a single bearing ball in older engines) at the contact point between the rocker and the valve, instead of metal sliding on metal. This reduces friction, uneven wear and "bell-mouthing" of

1085-467: The trade-off of less torque being produced at low RPM. The duration measurement for a camshaft is affected by the amount of lift that is chosen as the start and finish point of the measurement. A lift value of 0.050 in (1.3 mm) is often used as a standard measurement procedure, since this is considered most representative of the lift range that defines the RPM range in which the engine produces peak power. The power and idle characteristics of

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1120-418: The valve divided by the distance travelled by the pushrod effective. The ratio is determined by the ratio of the distances from the rocker arm's pivot point to the point where it touches the valve and the point where it touches the pushrod/camshaft. A rocker ratio greater than one essentially increases the camshaft's lift . Current automotive design favors rocker arm ratios of about 1.5:1 to 1.8:1. However, in

1155-445: The valve following the cam at its apex or prevent the valve from bouncing when it returns to the valve seat. This could be a result of a very steep rise of the lobe, where the cam follower separates from the cam lobe (due to the valvetrain inertia being greater than the closing force of the valve spring), leaving the valve open for longer than intended. Valve float causes a loss of power at high RPM and in extreme situations can result in

1190-407: The valvetrain, which can become problematic at higher engine speeds ( RPM ). For this reason, aluminum is often in engines that operate at higher RPM. Upgraded bearings for the rocker arm's fulcrum are also sometimes used in engines operating at high RPM. Diesel truck engines often use rocker arms made from cast iron (usually ductile), or forged carbon steel . Camshaft#Lift A camshaft

1225-410: Was replaced by BMW N42 engine . Rocker arm A rocker arm is a valvetrain component that typically transfers the motion of a pushrod in an overhead valve internal combustion engine to the corresponding intake/exhaust valve . Rocker arms in automobiles are typically made from stamped steel, or aluminum in higher-revving applications. Some rocker arms (called roller rockers ) include

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