Abstract: A camshaft assembly is disclosed which comprises an inner shaft (12), an outer tube (14) surrounding and rotatable relative to the inner shaft (12), and two groups of cam lobes mounted on the outer tube, the first group of cam lobes being fast in rotation with the outer tube, and each cam (10) lobe (18) of the second group being rotatably mounted on the outer surface of the tube (14) and connected for rotation with the inner shaft (12) by means of one or more drive members (50) passing through circumferentially elongated slots in the outer tube. In the invention, each drive member comprises a (15) drive component (50d) engaged with fixed alignment in the cam lobe (18) and a separate fastener (50b) that is rotatable to clamp the drive component against a flat surface on the inner shaft (12), each drive member (50) being constructed such that during the tightening of the fastener (50b) no relative (20) sliding movement is required at the interface between the drive component (50d) and the inner shaft (12).

Abstract: A valve drive assembly cooperable with gas exchange valves of an internal combustion engine having a cam shaft and at least one came support rotatably fixed and axially displaceable on the cam shaft and having at least two cam profiles selectively engageable with a roller provided on a follower engageable with a valve comprising a cam support having a cylindrical surface disposed coaxially with a cam shaft, provided with a pair of oppositely inclined, spiral grooves; and means selectively insertable into the grooves, coacting with side walls of such grooves as the cam shaft rotates to effect axial displacement of the cam support.

Abstract: The invention relates to a camshaft for an internal combustion engine with a shaft and at least one cam joined therewith, which is connected via a joining surface on the cam side with a joining surface on the shaft side. The joining surface on the cam side and alternatively or additionally the joining surface on the shaft side may be constructed such that they have a predefined roughness. Hereby, the friction between the shaft and the cam can be increased. The invention further relates to a cam for such a camshaft and a method for the manufacture of such a camshaft or respectively of such a cam.

Abstract: A camshaft for a combustion engine has a shaft and at least one cam thermally joined to a joining surface on the shaft side via a joining surface on the cam side. The shaft is embodied as a drawn and not additionally worked tube. Because of this the production of commercial vehicle camshafts can be realised in a more cost-effective manner since these do not have to be additionally ground or turned.

Abstract: A camshaft assembly may include a assembly and a shaft. The cam assembly may include a hollow structure with an interior surface and an exterior surface. A plurality of projections may be located on the exterior surface of the hollow structure. The interior surface of the cam assembly may define a recess axially aligned with at least one of the plurality of projections. At least one of the plurality of projections may define an undercut portion. The cam assembly may be coupled with the shaft.

Abstract: In a valve drive device, especially for an internal combustion engine including a camshaft with a cam element which is axially movably supported on the camshaft but in a rotationally fixed manner, the cam element includes a gate structure and an actuation device is provided with at least one shift element for engagement with the gate arrangement for axially displacing the cam element and the shift element has a rotationally asymmetrical basic shape in order to follow the gate structure when placed in engagement therewith.

Abstract: A camshaft assembly, particularly for use in an internal combustion engine, having a shaft base body and a plurality of cam parts. In order to be able to selectively shut down individual cylinders, cam parts are provided with cams which are arranged so as to be rotationally fixed and axially displaceable in relation to the shaft base body. Depending on a desired sequence of axially fixed and axially displaceable cam parts, it is proposed to arrange the axially displaceable cam parts on a longitudinally extending profile in an axially displaceable manner and to push the axially fixed cam parts—insofar as these are necesary—over or across the receiving area for the axially displaceable cam parts and to secure them to the shaft.

Abstract: A camshaft assembly may include a shaft and a lobe member fixed for rotation with the shaft. The lobe member may include a lobe extending radially outward from a base circle. The lobe may include a valve closing profile defined between a peak of the lobe and an ending point of the lobe on the base circle. The valve closing profile may define a closing flank and a closing ramp extending from an end of the closing flank to the ending point. The closing ramp may have a radial extent from the base circle at the end of the closing flank that is less than ten percent of the radial extent of the peak from the base circle and may have a first angular extent of at least ten degrees. A second angular extent defined between the peak and the ending point may be at least eighty degrees.

Abstract: An engine assembly may include a cylinder head defining a first bearing surface supporting a camshaft, a bearing cap fixed to the cylinder head and a lubrication rail. The first bearing surface may have a first oil inlet extending therethrough. The camshaft may define an axial bore, a first radial passage and a second radial passage. The first radial passage may extend from the axial bore through an outer circumference of the camshaft and may be in communication with the first oil inlet. The second radial passage may extend from the axial bore through an outer circumference of the camshaft. The bearing cap may be fixed to the cylinder head and include a first oil outlet in communication with the second radial passage. The lubrication rail may include a second oil inlet in communication with the first oil outlet and a first lubrication supply passage aligned with a camshaft lobe.

Abstract: In an internal combustion engine valve drive train shifting device including a camshaft having at least two shifting units arranged on the camshaft in spaced relationship, at least one coupling unit is provided interconnecting the at least two shifting units for shifting purposes.

Abstract: A valve drive assembly for selectively actuating a pair of valves of an internal combustion engine generally consisting of a pairs of cam supports rotatably fixed an axially displaceable on a camshaft, each provided with at least two cam profiles; means rotatably fixed and axially displaceable relative to the cam shaft, interposed between the cam supports; and means for selectively axially displacing the cam supports and the interposed means as a unit.

Abstract: In a valve drive arrangement for an internal combustion engine including a camshaft carrying axially movable cam elements provided with cams for operating gas exchange valves of the internal combustion engine and an actuation device having at least one shift element which is provided to shift cam element by means of a shifting gate between opposite axial positions, the valve drive arrangement has a change-over device for changing the axial shift direction of the shift element from one to the opposite axial position.

Abstract: A camshaft assembly has a rotationally drivable basic camshaft and at least one sliding piece which is mounted in the basic camshaft and can be displaced in the longitudinal direction of the latter, the sliding piece having at least one cam pack with at least two cams with different cam profiles, and having a switching device which has a switch guide plate for displacing the at least one sliding piece into different switching positions of the cams. It is provided in a camshaft of this type that the switching device has a switching shaft which can be rotated about the rotational axis of the basic camshaft with a switch guide plate which has a slotted-guide track, and a slotted-guide pin which is connected to the sliding piece and engages into the slotted-guide track.

Abstract: A valve lifter including a cylindrical portion, a crown portion having a crown surface, a chamfered portion formed on an outer periphery of the crown portion adjacent to an outer peripheral edge of the crown surface and tapered toward the crown surface, and a hard carbon film covering only the crown surface and the chamfered portion. The chamfered portion has a taper angle with respect to an outer peripheral surface of the cylindrical portion on which the hard carbon film is not formed, the taper angle being set to not more than 26.5°. The chamfered portion has a length extending from on a side of the crown surface toward a side of the cylindrical portion in an axial direction of the cylindrical portion, the length being set to not less than 1 mm.

Abstract: A camshaft assembly may include a assembly and a shaft. The cam assembly may include a hollow structure with an interior surface and an exterior surface. A plurality of projections may be located on the exterior surface of the hollow structure. The interior surface of the cam assembly may define a recess axially aligned with at least one of the plurality of projections. At least one of the plurality of projections may define an undercut portion. The cam assembly may be coupled with the shaft.

Abstract: A camshaft including a carrier element and a cam, in which the carrier element is composed of carrier segments arranged axially one behind the other along a longitudinal axis such that the carrier segments are axially displaceable relative to each other.

Abstract: An improved multi-port water distribution valve is disclosed together with the improved cam mechanism that significantly enhances the efficiency and effectiveness of the valve when used to distribute water to multiple sets of pop-up cleaning heads incorporated into the in-floor cleaning system of a swimming pool. Two forms of prior art distribution valves are disclosed as is the improved cam mechanism that, when used to replace the prior art cam in these devices, significantly improves their performance. Comparative data is provided demonstrating the results achieved with two different prior art valves operated with and without the improved cam. Embodiments of the invention suitable for use in existing six-port and five-port distribution valves are disclosed.

Abstract: A camshaft assembly may include a first shaft, a second shaft, a first lobe and a second lobe. The second shaft may be coaxial with and rotatable relative to the first shaft. The first lobe may be fixed for rotation with the first shaft and adapted to open a first valve in communication with an engine combustion chamber. The first lobe may define a first valve opening region having a first angular extent. The second lobe may be fixed for rotation with the second shaft and adapted to open a second valve in communication with the engine combustion chamber. The second lobe may define a second valve opening region having a second angular extent greater than the first angular extent.

Abstract: A valve train for an internal combustion engine for actuating gas exchange valves includes a camshaft in the form of a camshaft tube driven by a crankshaft of the internal combustion engine. A selector shaft is disposed in the camshaft tube. A surface of the selector shaft includes a shifting contour having an axial gradient. At least one cam carrier is disposed on the camshaft and axially displaceable but rotationally fixed with respect to the camshaft. Each cam carrier includes an identical base-circle portion and a plurality of cam profiles. A rotationally fixed but axially displaceable shifting sleeve is disposed between the camshaft tube and the rotatable selector shaft of each cam carrier. Each shifting sleeve includes a hole. A shilling ball is disposed in the hole of each shifting sleeve. The shifting ball is coupled with the shifting contour of the selector shaft so as to be guided by the selector shaft so as to axially displace the shifting sleeve by rotation of the selector shaft.

Abstract: The invention relates to a camshaft assembly comprising an inner shaft, an outer tube rotatable relative to the inner shaft, and two groups of cams mounted on the outer tube, the first group of cams being fast in rotation with the outer tube, and the second group being rotatably mounted on the outer surface of the tube and being connected for rotation with the inner shaft by means of connecting members that pass through circumferentially elongated slots in the outer tube. In the invention, the outer tube surrounds the inner shaft with clearance and the members connecting different ones of the cams of the second group to the inner shaft are inclined relative to one another and act to locate the axis of the inner shaft relative to the outer tube.

Abstract: A camshaft arrangement having two shafts disposed coaxially, one inside the other. A connecting element is inserted into a receptacle in the inner shaft, such that a part of the connecting element protrudes out of the receptacle, and that the protruding part is inserted at least partially in a recess, the recess is designed to be open at least toward an end face of the inner shaft cam, and that the protruding part has at least two opposite side surfaces contacting two corresponding inner surfaces of the recess of each inner shaft cam with a force fit. The further connecting element is designed as a radial pin pressed through a hole in the inner shaft cam element into a receptacle of the inner shaft.

Abstract: A valve-train assembly of an internal combustion engine is provided with a camshaft (1) that includes a carrier shaft (2), as well as a cam element (3) that can move on the carrier shaft between two axial positions and that has at least one cam group of directly adjacent cams (5, 6) with different cam lobes and an axial connecting link (8) constructed with a groove with outer guide walls (12, 13, 14, 15) for defining two intersecting connecting link pathways (9, 10), and with an activation pin (11) that can couple in the axial connecting link for moving the cam element in the direction of both connecting link pathways. In this way, the groove base of one connecting link pathway and the groove base of the other connecting link pathway should extend radially offset in height relative to each other, so that the connecting link pathway (9) with the radially lower groove base is also defined by inner guide walls (19, 20) that are formed by the offset in height.

Abstract: A continuous variable valve lift apparatus may include a camshaft, a first cam disposed on the camshaft, an actuating shaft parallel to the cam shaft, an actuating lever connected to the actuating shaft, a swing arm rotatably coupled to the actuating lever and an engine, a second cam pivotally connected to the swing arm and contacting the first cam to open a valve unit and a control portion which is connected to the actuating shaft and selectively rotates the actuating shaft for pivoting center of the swing arm to move.

Abstract: A valve train includes a a plurality of individual cam sleeves axially displaceable, relative to one another and disposed so as to form the camshaft, each of the plurality of individual cam sleeves including a plurality of different cam profiles each having a same base circle portion and being configured to engage, by switching, one of a plurality of gas exchange valves. A switching shaft is disposed inside the plurality of cam sleeves and configured to rotate together with the plurality of cam sleeves. An encircling switching contour is disposed inside each of the plurality of cam sleeves. A switching pin operatively connects one of the plurality of cam sleeves to the switching shaft, the switching pin configured to slide in the encircling switching contour. An actuator is operatively connected to the switching shaft so as to rotate the switching shaft relative to the plurality of cam sleeves.

Abstract: A volume store which has a substantially hollow cylindrical housing and a separating element displaceably disposed within the housing. The housing is fixedly disposed within a hollow chamber of a camshaft.

Abstract: An internal combustion engine includes a main enlarged member extended towards a camshaft for forming reed valve chambers. The main enlarged member is integrally provided on a head cover of the engine at a location at which reed valves for controlling supply of secondary air to an exhaust system are disposed. The main enlarged member is extended towards the camshaft for increasing volume of the reed valve chambers while avoiding the increase in size of the head cover. A recessed portion is provided on a cam cap fastened to a cylinder head of the engine. A portion of the main enlarged member is inserted into the recessed portion such that cam cap cooperates with the cylinder head for rotatably supporting the camshaft.

Abstract: An engine assembly may include a camshaft rotationally supported on an engine structure. The camshaft may include a first shaft, a second shaft located in and rotatable relative to the first shaft and a partial cam lobe located on the first shaft. The partial cam lobe may include a peak region and may define a partial bore. A radial distance defined by the partial bore between first and second circumferential ends of the partial bore may be greater than or equal to a radial width of the first shaft. The partial cam lobe may define a recess extending in a radial direction through the partial bore and into the partial cam lobe. The camshaft may include a sleeve located within a radial passage defined by the second shaft and the recess in the partial cam lobe and radially locating the partial cam lobe relative to the second shaft.

Abstract: A camshaft (1) is provided for a stroke-variable valve drive of an internal combustion engine with a carrier shaft (2) and a cam part (3) that is arranged locked in rotation and movable in the axial direction on the carrier shaft and that is assembled from a cam carrier (4) and a sleeve (5). The cam carrier has a cam group (7, 8) of directly adjacent cams (9, 10, 11, 12) with different cam strokes and an adapter end (6) on which the sleeve is mounted. The sleeve has a setting groove (17) in the form of a groove that extends across an extent of the sleeve and that is used for the specification of an axial setting groove track for an activation pin (18) moving the cam part on the carrier shaft. The setting groove is produced in the sleeve through non-metal-cutting shaping of sheet-metal material.

Abstract: A camshaft assembly method may include locating a first lobe member of a camshaft assembly on a first shaft of the assembly. A locking pin may be inserted into a first radial bore in the first lobe member and a second radial bore of the first shaft. The locking pin may have an annular wall defining a pin bore extending from a first end of the locking pin to a second end of the locking pin. A deforming member may be forced into the pin bore to displace the annular wall in an outward radial direction and into a frictional engagement with the first radial bore. The forcing may include a deforming member entering the pin bore at the first end of the locking pin and exiting the pin bore at the second end of the locking pin.

Abstract: A valve-mechanism-equipped engine having increased combustion efficiency is disclosed. The engine includes intake and exhaust rocker arms having a swing center line inclined relative to a rotation center line of a cam, and an intake valve and an exhaust valve inclined relative to a cylinder. A cam surface is inclined relative to the rotation center line of the cam. Slippers of the intake and exhaust rocker arms are in sliding contact with the cam surface.

Abstract: A camshaft may include a first shaft, a stop member, and a first lobe member. The first shaft may include an outer radial surface having a first recess extending radially therein. The stop member may be axially fixed within the first recess. The first lobe member may define an inner bore located on the outer radial surface of the first shaft. The first lobe member may include a second recess extending radially into the inner bore. The stop member may extend into the second recess to axially locate the first lobe member on the first shaft.

Abstract: A materials combination for a camshaft and follower of an engine valve train provides excellent wear resistance. The camshaft or camshaft lobes are made from a malleable cast iron and the cam followers are made from a carbonitrided 52100 or 4130 steel to provide excellent wear resistance equivalent to diamond-like coatings at greatly reduced cost.

Abstract: A valve train of an internal combustion engine with a camshaft (1) that has a carrier shaft (2) and a cam part (3) that is locked on rotation on the carrier shaft and is arranged displaceable in the axial direction and has at least one cam group (4a to 4c, 5a to 5c) of different elevations for variable actuation of a gas-exchange valve and a groove-shaped axial connecting link (10) with two connecting-link paths (11, 12) crossing its periphery, and with two actuation pins (13, 14) that can be coupled in the connecting-link paths for displacement of the cam part in the direction of the two connecting-link paths.

Abstract: A helical cam device for use with a wide variety of applications generally includes a first cam component, a second cam component and an axial guide. The cam components each have a helical cam track located on an axial end, so that coaxial alignment of the two cam components allows opposing cam tracks to contact and rotate against each other. The helical cam tracks, which are preferably divided into quadrant sections, are designed such that relative rotational movement between the cam components causes a corresponding relative axial movement. According to one embodiment, the axial guide is a cylindrical rod passing through the center of the cam components; in another embodiment, it is a cylindrical sleeve surrounding the cam components. Moreover, barrel slots, detents and/or truncated peaks can be used to control the travel of the cam components.

Abstract: A camshaft assembly may include a first shaft adapted to be rotationally driven, a first lobe member fixed for rotation with the first shaft, and a torsional damper fixed to the first shaft. The torsional damper may include a mass structure fixed to the first shaft and an elastic member disposed between and coupling the mass structure and the first shaft. The elastic member may have a spring constant providing a first sideband natural frequency and a second sideband natural frequency for the camshaft assembly.

Abstract: A cam for a camshaft of an internal combustion engine may include an axial extension with a holding contour for receiving a holding tool.

Abstract: A method for the linking of components to hollow shafts, preferably for producing camshafts, is disclosed where the components, especially cam rings, are manufactured so as to generate their function-related contour, that either a hardenable material is used for this purpose which, aside from its elastic deformability, after hardening still has a permissible plastic deformability of minor extent; or that subsequently the surface of the components, particularly the contact face of the cams, is subjected to a surface-hardening process. These components together with the hollow shaft to be deformed are placed into an IHPF tool in a manner to suit the respective function, and that in a second process step through the application of the IHPF process and due to the internal pressure exerted the components are joined to the hollow shaft in a force- and form-closing manner.

Abstract: An assembled camshaft includes an outer hollow camshaft body and an inner camshaft body disposed within the outer hollow camshaft body and mounted so as to rotate relative to it by a predetermined angle. The camshaft also includes at least two separate cam elements. A first cam element is connected with the inner camshaft body so as to rotate with it, and is disposed so as to rotate relative to the outer hollow camshaft body. A second cam element has at least two partial cam elements, in such a manner that a first partial cam element is disposed on the outer hollow camshaft body, so as to rotate with it, and a second partial cam element is connected with the inner camshaft body, so as to rotate with it, and is disposed so that it can be rotated relative to the outer hollow camshaft body.

Abstract: The present invention relates to a bearing device (1) for supporting a camshaft (2) in a cylinder head with at least two bearing blocks (3) which support the camshaft (2), and which are axially penetrated by the camshaft (2) to be supported in a first through-opening (6), and with a connection element (5), at which the at least two bearing blocks (3) are fastened in an aligned position, wherein the bearing blocks (3) together with the connection element (5) and the camshaft (2) form a prefabricatable module which is mountable in an aligned position at the cylinder head.

Abstract: A camshaft apparatus includes rolling bearings which support a camshaft rotatably, whereby a reduction in torque when an engine is started or is running at low speeds, a reduction in vibration of the camshaft and an extension of the lives of the bearings can be realized. In the rolling bearings, one rolling bearing is made to constitute a main ball bearing which restrains an axial relative movement of the camshaft relative to a shaft case, and the other rolling bearings are made to constitute a plurality of needle roller bearings, whereby a mechanical movement of the camshaft in an axial direction can be restricted in an ensured fashion by the main ball bearing. As to relative displacements due to thermal expansion or contraction of the camshaft and/or the shaft case, an axial relative displacement can be absorbed by needle rollers relatively moving on inter-cam outer circumferential surface areas.

Abstract: A valve train of an internal combustion engine is provided with a plurality of camshaft supports arranged on a support member of the engine, and a camshaft is supported on the camshaft supports. The camshaft has valve operating cams thereon for opening and closing engine valves of engine. A torque reducing mechanism is provided to apply a counter torque to the camshaft to suppress torque fluctuation of the camshaft caused by reaction forces applied to the cams by the engine valves. The torque reducing mechanism has a rotating member that rotates together with the camshaft, and a counterforce applying member for applying a counterforce to the rotating member to apply a counter torque to the camshaft. The counterforce applying member is supported on a connecting member connecting adjacent ones of the camshaft supports.

Abstract: A camshaft may include a first shaft, a bearing sleeve member located on and fixed to the first shaft, and a first lobe member located on the first shaft and displaceable between first and second positions. The first lobe member may be axially offset relative to the bearing sleeve member when in the first position to allow for machining of an outer surface of the bearing sleeve member and removal of machining debris from the outer surface. The first lobe member may be axially aligned with and bearingly supported on the bearing sleeve member when in the second position.

Abstract: A camshaft assembly configured to rotate about an axis of rotation within the engine of a motor vehicle to provide timing between cyclic operation of engine components is provided. The camshaft assembly includes a member for providing timing to a first engine component. The member includes a cam surface configured to drive the timing of the first engine component, and an opening. The camshaft assembly also includes a camshaft body cast to the member and configured to engage the opening of the member. The camshaft body includes a lobe configured to drive the timing of a second engine component, and a journal configured to allow efficient rotation of the camshaft body about the axis of rotation. The member is formed from a first material and the camshaft body is formed from a second material, thereby allowing the camshaft assembly to withstand two levels of stress.

Abstract: A camshaft system includes a number of cam lobes locked upon a cylindrical shaft. Bearings configured with one-piece bores and are engaged with the cylindrical shaft. The bearings are captured upon the shaft by the locked-on cam lobes.

Abstract: A camshaft assembly may include a assembly and a shaft. The cam assembly may include a hollow structure with an interior surface and an exterior surface. A plurality of projections may be located on the exterior surface of the hollow structure. The interior surface of the cam assembly may define a recess axially aligned with at least one of the plurality of projections. At least one of the plurality of projections may define an undercut portion. The cam assembly may be coupled with the shaft.

Abstract: An internal combustion engine for a vehicle, such as a motorcycle, includes a crankcase, two banks of cylinders projecting from the crankcase in a 56-57 degree V-configuration, a plurality of pushrods, and a plurality of camshafts supported by the crankcase. The two banks of cylinders include a first cylinder bank that projects from the crankcase to a first cylinder head, and a second cylinder bank that projects from the crankcase to a second cylinder head. The plurality of intake and exhaust valve pushrods extend between the crankcase and the first and second cylinder heads, driven by one intake camshaft and two exhaust camshafts.

Abstract: A shaft comprising functional elements, such as an assembled camshaft for an internal combustion engine, a method for producing such shafts, and internal combustion engines equipped with such shafts. The functional elements each have a bore and are produced separately from the shaft main body, and the bore is subsequently press fit onto the shaft body to attach the functional element in an axially and rotationally fixed manner. The shaft is also provided with at least one roller bearing that includes at least one undivided roller bearing element which is mounted on the shaft body between two functional elements, for example, by press fitting.

Abstract: A device for hydraulic control of gas exchange valves of a reciprocating internal combustion engine which has slave cylinders in operative connection with one or more gas exchange valves and master actuators in operative connection with at least one cam provided with a basic and cam profile of a camshaft that is rotatably driven by the engine and can be hydraulically connected to the slave cylinders. The device also has a control device controlled by an actuating member, the device controlling the volume of hydraulic liquid fed to the slave cylinders, and at least one feed line, via which low pressure liquid from a pressure source can be fed to the device by means of at least one non-return valve. The actuators have displaceable vanes, a component carrying the vanes, and cells limited by walls. The vanes are in operative connection with the basic and cam profile of the cam.

Abstract: The invention relates to a valve train for gas exchange valves of an internal combustion engine, having a base camshaft, a plurality of cam carriers, which are arranged in a rotationally fixed and axially movable way on the base camshaft, as well as stopping devices for retaining the cam carriers in defined displacement positions along the base camshaft, with the stopping devices comprising in each case a pressure-applying element, which is inserted into a recess of the base camshaft and pressed in the radial direction of the base camshaft against an opposite inner circumferential section of the cam carrier. In order to counteract noise generation in the valve train, a first variant of the invention provides an additional pressure-applying element at an axial distance from the pressure-applying element. This additional pressure-applying element is pressed against an opposite inner circumferential section of the cam carrier.

Abstract: An Otto cycle, Atkinson cycle or supercharged internal combustion engine (10) and a timing mechanism therefor. The engine comprising: a cylinder (14) and a piston (12) reciprocally mounted within the cylinder (14) in which reciprocating movement of the piston is converted into rotational movement of an output shaft (28) by way of rollers (20, 24) engaging primary (22) and secondary (26) cam means which are affixed to, and rotatable with, the output shaft (28). The timing mechanism comprising cam means (52, 53) mounted on, and rotatable in unison with, the output shaft (28), a cam follower (54, 55) arranged to engage the cam means (52) and a linkage connecting the cam follower to a pivoting rocker arm for actuating the engine's induction and exhaust valves, the rocker arm pivot being adapted to be moveable on an arcuate locus centred on the axis of the output shaft (28).