Abstract: An hydraulically controlled actuator for activating a valve, especially for activating a gas-exchange valve in a combustion cylinder of an internal combustion engine, which includes two fluid-filled pressure chambers having controllable chamber volumes and a movable operating piston which delimits the pressure chambers by piston sides facing away from one another, the operating piston acting upon the valve and having an effective closing area acted upon by fluid pressure in the pressure chambers to close the valve and an effective opening area acted upon by the fluid pressure to open the valve. To influence the kinematics of the opening and closing movement of the valve, the operating piston is such that the surface area of at least one of the two effective areas changes along the sliding path of the operating piston.

Abstract: A valve driving device including a tappet assembly adapted to slide in a tappet guide hole to drive a valve and including a high-speed center tappet and low-speed side tappet; and a high-speed center cam and a low-speed side cam provided corresponding to the center tappet and the side tappet. A depression is formed which is depressed from a base circle to roughly the same profile as a shaft section of the camshaft so that the cam portion over a predetermined angle range where a cam nose section is not formed in the centrally located center cam is smaller than the base circles of the outside located side cams in profile.

Abstract: A valve operating system for an internal combustion engine including a main valve lifter, a subsidiary valve lifter, a low-speed cam operating the main valve lifter, a high-speed cam operating the subsidiary valve lifter, a connecting device switched over between a non-connecting state in which the valve lifters are disconnected from each other, and a connecting state in which the valve lifters are connected to each other, a valve spring for biasing the valve in a closing direction, a lifter spring for biasing the subsidiary valve lifter toward the cam; thus, in a low-speed mode, that is non-connected states, an influence of a load of the lifter spring on the valve can be prevented, and in a high-speed mode, that is connected states, a sum total of loads of the valve spring and the lifter spring cap be applied to both of the valve lifters to improve the closing responsiveness of the valve.

Abstract: The invention relates to a mechanical valve play compensation element for a valve drive on a piston combustion engine, comprising a first pressure part (1) which is axially displaceable in relation to a second pressure part (2) and which is fixed in such a way that it can turn about the axis of displacement; a torsion spring element (10) which acts between the first pressure part (1) and the second pressure part (2) and is axially flexible at least to a certain extent; and at least one helical surface (9.1) on the first pressure part (1), to which a corresponding helical surface (9.2) on the second pressure part (2) is allocated, these forming a pair of helical surfaces (9). The surfaces of the helical surface pair (9) are configured as a rough surface and are pressed against each other by the torsion spring element (10).

Abstract: A cylinder deactivation arrangement for an engine is provided. The arrangement includes an engine with main oiling circuit passages and lifter oil gallery control circuit passages formed internal to a cylinder block of the engine. The lifter oil gallery control circuit is arranged so as to provide an oil flow path internal to the cylinder block from the main oiling circuit to the deactivating lifter. A lifter is positioned in the cylinder block and arranged in fluid communication with the lifter oil gallery control circuit. A control valve is positioned in the cylinder block and arranged in fluid communication with the main oiling circuit and the lifter oil gallery control circuit. The control valve is arranged to allow selective fluid communication of oil from the main oiling circuit to the lifter oil gallery control circuit to selectively control actuation of the lifter.

Abstract: A valve lifter for an internal combustion engine comprises an outer body, an inner body and at least one pin. The inner body is movable with respect to the outer body, and the at least one pin is movable in response to hydraulic pressure into the groove to lock the outer body against movement relative to the inner body.

Abstract: The present invention is related to a valve lifter for use in an internal combustion engine. The valve lifter comprises a body adapted to be reciprocally slidable within a valve lifter bore of an engine. The valve lifter includes a rotably mounted cam roller engaging the cam lobe of a cam-shaft where the cam lobe operates to drive the valve lifter body towards a valve open position. The valve lifter may also include an auxiliary roller rotatably mounted in the valve lifter body and engaging the cam roller where the force from the cam lobe is transferred to the lifter body through both the cam roller and auxiliary roller. The present invention includes a method of making a valve lifter by creating grooves in the walls of the recess to aid in the lubrication of the rollers.

Abstract: A valve train with a hydraulic lifter in an engine, and a method of configuring a hydraulic lifter of an engine, are disclosed. The valve train includes a valve, a cam, and at least one coupling component. The valve train further includes the hydraulic lifter, which has a nominal length and is coupled at least indirectly between the valve and the cam by way of the at least one coupling component. The valve train additionally includes a mechanism for varying the nominal length of the hydraulic lifter so that the nominal length is substantially closer to a minimum length of the hydraulic lifter than to a maximum length of the hydraulic lifter.

Abstract: A deactivation valve lifter includes a lifter body. The body defines at least one annular pin chamber therein. The lifter body has a first end configured for engaging a cam of an engine. A pin housing includes a pin housing wall and pin housing bottom. The pin housing wall includes an outer surface. The pin housing bottom defines a radially directed pin bore. The pin housing is concentrically disposed within the lifter body such that the outer surface of the pin housing wall is adjacent to at least a portion of an inner wall of the lifter body. A deactivation pin assembly is disposed within the pin bore and includes pin members. A portion of each pin member is disposed within the annular pin chamber to thereby couple the lifter body to the pin housing. An external lost motion spring is coupled to the body and pin housing.

Abstract: An anti-rotation guide for a deactivation hydraulic valve lifter for an internal combustion engine. The guide includes a through bore accommodating of a hydraulic valve lifter and is sized such that the outer end of the lifter may be inserted into the through bore of the guide. The guide is securable to the engine such that the lifter is reciprocable within the guide. The guide is provided with two opposing keepers for mating with corresponding flats on the lifter to prevent rotation of the lifter. Further, a keyway means is provided in the guide and lifter to prevent the lifter being inserted into the guide 180° from the correct orientation.

Abstract: A hydraulic system (1) for a switchable valve drive element (10) of an internal combustion engine (33) is provided and includes a throttled connection (13) created from a second channel (9), used to actuate a hydraulic play-compensation element (11) using hydraulic fluid, directly to an external radial side (12) of a coupling element (8). The coupling element (8) is supplied by a first channel (7) with the switching hydraulic pressure. These measures make it possible to keep the first channel (7) as free as possible of undesired air.

Abstract: A connectable bucket tappet having a ring shaped section and avoiding a receiving element for a coupling device which was previously joined thereto in a single piece. A separate, sleeve-shaped component is arranged near the base of the ring shaped section. The component is used for sectionally accommodating a slider for coupling the ring shaped section to a central circular section.

Abstract: An anti-rotation guide for preventing rotation of a roller follower valve lifter in an internal combustion engine. The guide has an outer surface for engaging an engine bore and an inner surface for slidably receiving the lifter. One end of the guide includes an anti-rotation feature for cooperating with a mating feature on the lifter, preferably flats although other configurations are contemplated within the scope of the invention. The anti-rotation feature may take any of a plurality of shapes, including but not limited to an arm and tang, a flap, and an orifice flat. The guide is installed from an opening in the engine bore proximate a camshaft disposed in the engine block. The cooperating features prevent axial rotation of a lifter within the sleeve but do not inhibit axial or reciprocal motion of the lifter.

Abstract: An internal combustion engine having a valve train that includes a switchable cam follower is provided. The cam follower (20) has a generally cylindrical shape and can move longitudinally in a receptacle (21) of the engine (22), and is acted upon at one axial end by a cam (23) of a camshaft and at the other axial end indirectly or directly by a gas exchange valve of the valve train. A main oil gallery (24) is arranged in the internal combustion engine (22) for introducing hydraulic medium to a valve lash adjustment element arranged in the cam follower (20).

Abstract: The invention proposes a tappet (1) in a valve train of an internal combustion engine having a bottom camshaft for acting on a tappet push rod, said tappet being arranged with a housing (2) for axial displacement, but secured against rotation, in a guide bore (3) of the internal combustion engine (3a) or of a component connected to the internal combustion engine, said housing (2) comprising on one front end (4), two cheek-like extensions (5) that are situated diametrically opposite each other and are connected by an axle (6) on which a rotary roller (7) extends for making direct contact with a cam, said front end (4) comprising a transverse region (5) that connects the extensions (5) axially Inside and has a cylindrical shape in a length direction of the roller (7), and said guide bore (3) being intersected by two passages (12, 13) for routing hydraulic medium to the tappet (1), wherein a radius center point (M) of the transverse region (8) of the one front end (4) is situated with a lateral offset to a longi

Abstract: A race car valve lifter for more reliable engine function for a race car. The race car valve lifter includes a tubular member having open first and second ends and a bore being disposed therethrough; and also includes a body being slidably disposed in the bore and through the open first end of the tubular member; and further includes a plug member being removably and securely disposed in the open second end of the tubular member; and also includes a spring member being disposed in the bore of the tubular member for biasing a portion of the body through the open first end of the tubular member.

Abstract: The present invention relates to a method for fabricating a roller follower assembly, comprising the steps of fabricating a lash adjuster body, fabricating a roller follower body, fabricating a leakdown plunger, fabricating a socket, wherein at least one of the lash adjuster body, roller follower body, leakdown plunger, and socket is fabricated at least in part by forging.

Abstract: The invention relates to a valve mechanism with a variable valve opening cross section for use in an internal combustion engine and having a gas exchange valve acted on by the force of a valve spring and displaceable axially back and forth inside a guide by a valve control unit; the position of the sealing slide relative to the gas exchange valve in the axial direction is continuously variable by means of an adjusting unit. A sealing slide disposed coaxially to the gas exchange valve, is acted upon by the force of a coupling spring, and is displaceable axially back and forth by the valve control unit. The position of the sealing slide is variable in the axial direction relative to the gas exchange valve by means of an adjusting unit.

Abstract: A valve actuator assembly for actuating a valve, the valve having a longitudinal axis includes an electrohydraulic actuator being displaced a lateral distance from the valve longitudinal axis, and a rocker arm being rotatable about a hinge point, a first arm portion extending from the hinge point to a proximal end and a second arm portion extending from the hinge point to a distal end, the proximal end being operably coupled to the second stage piston and the distal end being operably coupled to the valve, the fist arm portion being shorter than the second arm portion, the rocker arm spanning the lateral distance. A method of stroke amplification is further included.

Abstract: A valve driving device including a tappet assembly adapted to slide in a tappet guide hole to drive a valve and including a high-speed center tappet and low-speed side tappet; and a high-speed center cam and a low-speed side cam provided corresponding to the center tappet and the side tappet. A depression is formed which is depressed from a base circle to roughly the same profile as a shaft section of the camshaft so that the cam portion over a predetermined angle range where a cam nose section is not formed in the centrally located center cam is smaller than the base circles of the outside located side cams in profile.

Abstract: In an internal combustion engine with a motor block (6) and a longitudinal extending anti-rotation guide (5), which includes receiving recesses situated at apportioned spatial distances, one from the other to receive valve tappets and is affixed in a receiving groove of the motor block (6). The guide (5) is constructed as an injection molded component with a one-piece, molded-on, elastically expanded or deformable clip, which engages in a complementary receiving contour on the motor block (6).

Abstract: In a variable phased valve lifter of an internal combustion engine, a roller lifter is allowed to move along a constraining member of a constraining mechanism, and the constraining mechanism is allowed to move freely in a direction substantially parallel to a line perpendicular to the flat surface machined onto the roller lifter. As the roller lifter moves through its arcuate path, the parallel flat surface(s) of the roller lifter will slide across the constraining member(s) of the constraining mechanism, and end members of the constraining mechanism slide fore-and-aft within stationary blocks. The roller lifter is thus prevented from rotating about its longitudinal axis as it moves in arcuate fashion in cooperation with the constraining mechanism, maintaining line contact between the roller and cam lobe of the camshaft.

Abstract: A variable valve lift device according to the present invention includes a tappet case, a sway member and a sliding member. The tappet case makes contact with one of cams arranged at a camshaft driven rotationally due to a crankshaft of an internal combustion engine and which is driven reciprocally due to the rotation of the cam. The sway member is so supported in the tappet case as to allow sway of the sway member and has a sliding face displacing a valve stem in an axial direction of the valve stem. The sliding member is so arranged in the tappet case as to allow sliding of the sliding member and sways the sway member when the sliding member is slid.

Abstract: A connection between a shaft end of a gas exchange valve of an internal combustion engine and a sleevelike actuating piston of a valve actuator, has at least two shell-like key pieces, surrounding the shaft end and on whose radially outer circumferential surface there is a conically tapering portion, pointing away from a combustion chamber of the engine, and extending in complementary fashion to the cone angle of a radially inner conical portion of a conical fastening sleeve that includes the key pieces, and the conical fastening sleeve and the key pieces can be braced axially against one another. Protrusions and recesses engaging one another are provided on the radially inner circumferential surface of the key pieces and on the radially outer circumferential surface of the shaft end of the gas exchange valve. The conical fastening sleeve is formed by the actuating piston and the actuating piston and the key pieces have threaded portions that can be screwed into one another.

Abstract: A fuel supply apparatus capable of reducing the abrasion of a driving cam and a tappet without increasing the dimensions and weight of the apparatus. This fuel supply apparatus is provided with a tappet which has a pressure receiving surface contacting the driving cam of an engine. The tappet is provided at the part of a outer surface thereof which is in the vicinity of an outer circumference of the pressure receiving surface with a groove adapted to prevent the local concentration of stress on the tappet and having a V-shaped, semicircular or U-shaped cross section.

Abstract: The present invention relates to a valve lifter body, comprising an outer surface, enclosing a first cavity and a second cavity, wherein the first cavity includes a first inner surface configured to house a cylindrical insert, the second cavity includes a second inner surface cylindrically shaped, and at least one of the cavities is fabricated through forging.

Abstract: To provide a high performance four-stroke internal combustion engine wherein an increase in a side of a cylinder head is prevented and a valve resting mechanism is provided for a valve lifter. In a four-stroke internal combustion engine with a valve resting mechanism includes a valve lifter having a valve resting mechanism interposed between a valve motion cam and a stem of a poppet valve and a valve lifter spring is provided for biasing the valve lifter in a direction in which the valve lifter is normally held in contact with the valve motion cam. A slide pin holder is pressed against the valve lifter by a spring force of the valve lifter spring that is provided on the valve lifter while a shim portion having a predetermined thickness for controlling a relative positional relationship with the valve lifter is formed integrally with a valve lifter top wall.

Abstract: Several embodiments of anti-rotation devices for precluding rotation of the valve actuating lifters or tappet bodies caused by the action of the cam lobe on the engaged surface of the lifter. In each embodiment, the anti-rotation function is achieved without adding to the reciprocating masses of the engine.

Abstract: A connection between a shaft end of a gas exchange valve of an internal combustion engine and a final control element of a valve actuator, with at least two shell-shaped wedge-shaped pieces, surrounding the shaft end and braced on the final control element, whose radially outer circumferential surface extends conically and which are surrounded by at least one conical clamping sleeve whose radially inner circumferential surface extends complimentary to the cone angle of the wedge-shaped pieces, wherein on the radially inner circumferential surface of the wedge-shaped pieces and on the radially outer circumferential surface of the shaft end of the gas exchange valve, protrusions and recesses that mesh with one another are provided.

Abstract: The invention relates to a roller tappet, with at least the shaft made from plastic. The aim of the invention is to achieve a weight-saving mounting of the roller. The aim is achieved, in that the axle carrying the roller may be clipped into the insert, which is of unitary construction with the shaft piece.

Abstract: A tappet (1) for the transfer of a lifting motion to a sliding part is provided having two parts, including a circular shaped section (2) with a base (5) connected to it as one piece and a separate dome-shaped socket (9) connected to the base (5) made of thin-walled material with a contact surface (10) for the sliding part. The tappet (1), whose socket (9) extends over a considerable length of the circular shaped section (2), can be economically manufactured.

Abstract: During assembly, shipping and handling before a mechanically-actuated fuel injector is installed into an internal combustion engine, the fuel injector tappet often accidentally disconnects from the fuel injector body. This separation of the tappet from the fuel injector body is caused by a force placed upon the tappet by a biasing means, such as a spring, that pushes the tappet away from the injector body. The fuel injector of the present application solves this problem through the interaction of a retention clip, a retention opening in the fuel injector body, and a retention slot in the fuel injector tappet. The retention clip has a body and a protrusion. The retention clip body is contained within the fuel injector body, and the protrusion extends through the retention opening and into the retention slot. After it is assembled, the fuel injector of the present application remains connected during shipping and handling and permits easy installation into an internal combustion engine.

Abstract: Cylinder deactivation apparatus includes switching valve actuators controlled by rotary valve sleeves surrounding each of the actuators. In a preferred embodiment, the sleeves act to admit continuous pressurized oil to internal lash adjuster mechanisms and selectively control oil flow from a lash adjuster mechanism inlet to a deactivator switching mechanism and discharge of pressure oil from the deactivator switching mechanism. A single oil supply provides pressurized oil to both conventional and deactivation valve actuators for lubrication of associated valve mechanisms and operation of internal lash adjusters as well as for operation of the cylinder deactivation mechanisms. In a valve-actuating position, the rotary sleeve drains oil from the deactivating mechanism so that associated engine valves are operated normally.

Abstract: The invention relates to a variable valve train (1) for a cam-actuated lifting valve (13) of an internal combustion engine, which valve (13) is loaded by a closing spring (13a) acting against the direction of opening, with an approximately cylindrical force application element (2) located between a cam (14) and the valve (13), whose length can be adjusted hydraulically and whose exterior cylindrical wall face (3) is slidable in a fixed guide cylinder (4), said element (2) being provided with a pressure piston (6) longitudinally slidable in a cylinder (5), which piston (6) is adjacent to a pressure chamber (7) into which opens a pressure channel (8) departing from a port (9) in the wall face (3) of the force application element (2), a fixed pressure line (11) opening into the guide cylinder (4) in the area of the port (9), which line (11) can be subjected to hydraulic high pressure (pH) permitting hydraulic activation of the valve (13).

Abstract: In a valve train of an internal combustion engine having a switchable support element (1), the lost motion spring (18) of the support element (1) is arranged axially offset next to the support element (1) while being coupled to an inner element (3) of the support element (1) by a crossbar (20). Due to this externally positioned spring (18), the support element (1) requires only a relatively small design space.

Abstract: Variable valve mechanisms utilize magnetorheological fluid (MRF) in lost motion devices for controlling lift and timing of engine valves and the like. The lost motion devices are designed with either of two operational modes, a direct shear mode and a valve mode. In the shear mode, the MR fluid is retained between relatively movable shear surfaces of a lost motion device and the relative motion is controlled by varying the shear strength of the fluid by a magnetic field applied to the MR fluid between the shear surfaces. In the valve mode, the flow rate of MR fluid through an orifice is controlled by varying the magnetic field to control the flow viscosity of the fluid passing through the orifice. The lost motion device units may be applied directly between an input cam and an output valve or may be applied to a pivot for a finger follower or another type of valve actuation.

Abstract: The invention relates to a connection (42) between a shaft end (22) of a gas exchange valve (1) of an internal combustion engine and a sleevelike actuating piston (2) of a valve actuator (4), having at least two shell-like key pieces (44, 46), surrounding the shaft end (22) and on whose radially outer circumferential surface there is a conically tapering portion (50), pointing away from a combustion chamber of the engine, which portion extends in complementary fashion to the cone angle of a radially inner conical portion (60) of a conical fastening sleeve that includes the key pieces (44, 46), and the conical fastening sleeve and the key pieces (44, 46) can be braced axially against one another, and protrusions (70) and recesses (72) engaging one another are provided on the radially inner circumferential surface of the key pieces (44, 46) and on the radially outer circumferential surface of the shaft end (22) of the gas exchange valve (1).

Abstract: The cup tappet (1) of the invention for a valve train of an internal combustion engine comprises a hollow cylindrical skirt (2) whose one end (3) is connected to a bottom (5) for making contact with a cam. The skirt (2) has a clearly smaller height than the overall height of the cup tappet (1), and the bottom (5) rises in a roof-like taper from said end (3). By virtue of this configuration, the bottom (5) has a very high rigidity, so that it is possible to minimize its thickness ‘d’ significantly compared to thicknesses of prior art cup tappet bottoms.

Abstract: What is proposed is a switchable tappet (1) for the direct transmission of a cam lift to a tappet push rod. The tappet (1) comprises a hydraulic clearance compensation element (31) and has an excellent hydraulic rigidity compared to the prior art. This is achieved by a leak gap positioned radially very far outwards. This leak gap is situated directly between a housing (2) and a pressure piston (4) which, in its turn, encloses an inner element (11) that acts on a tappet push rod.

Abstract: A tappet is used in a valve-operating mechanism of an internal combustion engine. The tappet has a top wall and the upper surface of the top wall is engaged with a cam. The lower surface is engaged on a poppet valve which moves up and down. A downward projection which has a recess for storing lubricating oil is formed in the middle of the lower surface of the top wall of the tappet, thereby lubricating interfaces with the cam or valve to improve frictional or wear resistance.

Abstract: The invention proposes a switchable tappet (1) for the direct transmission of a cam lift to a tappet push rod. A coiled compression spring (15), used as a lost motion spring, for loading the inner element (4) is shifted axially out of a housing (2). For this purpose, the inner element (4) comprises an extension (15a) that projects out of the housing (2) and is surrounded by the coiled compression spring (15). This measure contributes to minimizing the total mass of the switchable tappet (1) because the overall length of the housing (2) is shortened.

Abstract: In a valve train of an internal combustion engine, which valve train comprises an elongate anti-rotation bridge (6) comprising receptions spaced behind one another for receiving valve tappets configured as roller tappets (4), one of which tappets is arranged in each reception and is directed with a tappet roller (3) toward a cam (2) of a camshaft (1), the roller tappet (4) of the invention comprises on an outer peripheral surface, raised tappet contours (10, 11) that engage into retention grooves of the bridge (6) within the reception.

Abstract: In a switching element (1) for a valve train of an internal combustion engine for switching to different valve lifts, said switching element (1) comprising an outer element (2) having an inner element (4) arranged for axial displacement therein, each of the outer and the inner element (2, 4) comprising a reception (11, 9) aligned to each other in a relative position, at least one piston (10) being arranged in at least one of the receptions (11, 9) for sliding toward the other of the receptions (9, 11) to couple the inner element (4) to the outer element (2) in said relative position, and a high-position stop for defining said relative position being arranged between the inner and the outer element (4, 2), at least one part of the high-position stop is configured as an adjustable, separate element (13). This element (13) cooperates through a preferably conical section (15) of its outer periphery with a complementary chamfer (18) on one end (17) of a guide (16) in the outer element (2).

Abstract: The present invention is related to a valve lifter for use in an internal combustion engine. The valve lifter comprises a body adapted to be reciprocally slidable within a valve lifter bore of an engine. The valve lifter includes a rotably mounted cam roller engaging the cam lobe of a cam-shaft where the cam lobe operates to drive the valve lifter body towards a valve open position. The valve lifter may also include an auxiliary roller rotatably mounted in the valve lifter body and engaging the cam roller where the force from the cam lobe is transferred to the lifter body through both the cam roller and auxiliary roller. The present invention includes a method of making a valve lifter by creating grooves in the walls of the recess to aid in the lubrication of the rollers.

Abstract: A hydraulic lash adjuster has a plunger assembly the outer end of which can be moved inwardly until the inner end abuts a seal and closes a high pressure chamber, thus preventing further movement. This accommodates any necessary movement of a valve towards its closing position to ensure proper closure. Consequently, net-shaped cams wherein the base circle is not necessarily accurately concentric may be used. A leaf spring ensures opening of the chamber when the base circle of the cam is next reached.

Abstract: The invention proposes a switching element (1) for a valve train of an internal combustion engine, said switching element comprising an outer element (2) and an inner element (4) that is arranged for axial displacement in a bore (3) of the outer element (2), each of the outer element (2) and the inner element (4) comprising at least one reception (12, 9) aligned to each other in an axially distant relative position which is achieved through a lost motion spring (8), at least one piston (10) being arranged in at least one of the receptions (12, 9) for sliding toward the other of the receptions (12, 9) to couple the inner element (4) to the outer element (2) in said relative position, and a high-position stop for defining said relative position being arranged between the inner element (4) and the outer element (2).

Abstract: The present invention relates to a variable valve lift system that varies a valve lift in two stages by selectively rigidly engaging a tappet shim.

Abstract: An internal combustion engine tapered push rod assembly construction is disclosed, as well as a novel method of partially making the assembly elongated body section component from tubular push rod feedstock by removing excess exterior feedstock to form the body section exterior taper rather than by known conventional radial compression of feedstock exterior material that otherwise results in an unwanted feedstock reduced internal diameter, and an unwanted increased body section wall thickness configuration.

Abstract: In a valve train of an internal combustion engine having a switchable support element (1), the lost motion spring (18) of the support element (1) is arranged axially offset next to the support element (1) while being coupled to an inner element (3) of the support element (1) by a crossbar (20). Due to this externally positioned spring (18), the support element (1) requires only a relatively small design space.

Abstract: A valve pause mechanism of a four-stroke internal combustion engine includes a valve pause mechanism. A valve lifter fitted between a valve cam and a valve stem of a poppet valve is always pressed in a direction in which the valve lifter contacts the valve cam with a lifter spring. However, a slide pin is fitted into a slide pin holder fitted in the valve lifter so that a slide pin can slide in a direction perpendicular to the valve stem. A stem working face in contact with the valve stem of the poppet valve and a stem through hole that the valve stem pierces are both adjacently formed in the slide pin and a slide pin driving mechanism. The slide pin driving mechanism selectively makes the stem working face and the stem through hole face the valve stem by moving the slide pin. A side of the slide pin at the back of the stem working face is chamfered across the stem through hole.