JP6628205B2 - Valve stem seal - Google Patents

Description

  The present invention relates to a valve stem seal, and more particularly to a valve stem seal used in an internal combustion engine of an automobile.

  BACKGROUND ART Conventionally, in an internal combustion engine, a valve stem seal has been used to seal a space between a valve stem and a valve guide of a valve that reciprocates between a cam side and a cylinder side. The valve stem seal supplies the lubricating oil between the valve guide and the valve stem so as to smoothly slide the valve stem, and also supplies the lubricating oil in order to prevent problems such as generation of white smoke. To prevent inflow into ports and cylinders. FIG. 4 is a cross-sectional view showing a state in which a conventional valve stem seal is mounted. As shown in FIG. 4, a conventional valve stem seal 100 includes a metal reinforcing ring 101 and an elastic body 102 formed integrally with the reinforcing ring 101 and made of an elastic body. The valve stem 110 includes a seal lip 103 with which the valve stem 110 slidably contacts. In the valve stem seal 100, the reinforcing ring 101 is press-fitted into the end of the valve guide 111, fitted to the valve guide 111 by metal fitting, and the seal lip 103 comes into contact with the valve stem 110 to lubricate the oil as described above. Is controlled (for example, see Patent Document 1).

JP-A-2004-19852

  As described above, in the conventional valve stem seal 100, the metal reinforcing ring 101 is fitted to the valve guide 111, and the metal valve is firmly attached to the valve guide 111 by metal fitting. The valve stem seal 100 is prevented from falling out of the valve guide 111 even when receiving a high back pressure due to downsizing of the engine or mounting of a turbocharger due to a demand for further reduction in fuel consumption. However, it is necessary to apply a large load to the reinforcing ring 101 in order to metal-fit the reinforcing ring 101 to the valve guide 111, and the conventional valve stem seal 100 is difficult to attach to the valve guide 111. Further, the conventional valve stem seal 100 is difficult to remove from the valve guide 111, and there is a possibility that the valve guide 111 may be damaged when it is removed for maintenance or the like.

  For this reason, the conventional valve stem seal employs a structure in which metal fitting to the valve guide is adopted, mounting to the valve guide is easy, and removal from the valve guide for maintenance or the like is easy. Was sought.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a valve stem seal capable of facilitating attachment to a valve guide and facilitating removal from the valve guide. It is in.

  In order to achieve the above object, a valve stem seal according to the present invention includes a metal reinforcing member including an annular reinforcing ring portion centered on an axis and an engaging portion engageable with a valve guide extending from the reinforcing ring portion. A metal ring, and a ring-shaped elastic portion formed around an axis formed of an elastic member attached to the reinforcing ring portion, wherein the elastic portion is in contact with the valve stem. And a back pressure lip abutting on the valve stem disposed on the engagement portion side of the metal ring from the seal lip, wherein the engagement portion of the metal ring is A plurality of claws extending gradually away from the axis along the axial direction, wherein the claws are deformable to extend in the axial direction, and each of the claws is directed toward the axis; Can be engaged with the protruding valve guide And having the formed engaging projections.

  In the valve stem seal according to one aspect of the present invention, in the metal ring, the engaging portion extends from one end of the reinforcing ring portion in the axial direction, and the reinforcing ring portion is an outer surface of the reinforcing ring. Has an annular groove formed at the one end.

  In the valve stem seal according to one aspect of the present invention, the plurality of claw portions of the engagement portion are formed by cutting an annular portion extending in the axial direction from the reinforcing ring along the axis. .

  In the valve stem seal according to one aspect of the present invention, the engagement protrusion of the claw portion can be engaged with a groove formed on one end side of the valve guide.

  In the valve stem seal according to one aspect of the present invention, the elastic body portion includes a positioning protrusion that is an annular protrusion extending from the back lip to the engagement portion side in the axial direction. When the abutment is in contact with the valve guide, the engagement portion is positioned at a position where it can be engaged with the valve guide.

  ADVANTAGE OF THE INVENTION According to the valve stem seal which concerns on this invention, while being easily attached to a valve guide, removal from a valve guide can be made easy.

FIG. 2 is a sectional view taken along an axis for illustrating a schematic structure of a valve stem seal according to the embodiment of the present invention. FIG. 2 is a side view of the valve stem seal shown in FIG. 1. It is sectional drawing which follows the axis of the valve stem seal which concerns on embodiment of this invention in the state attached to the valve guide. It is sectional drawing which shows the conventional valve stem seal in the attached state.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a sectional view taken along an axis for showing a schematic structure of a valve stem seal according to an embodiment of the present invention. A valve stem seal 1 according to an embodiment of the present invention is used in a valve train of an internal combustion engine of an automobile, and a valve stem of a valve for communicating and shutting off between a cylinder and a port, and the valve stem is inserted therethrough. One end faces the cam side and the other end seals with the valve guide facing the cylinder side. Hereinafter, for convenience of description, the reference numeral A indicates the cam side and the reference numeral B indicates the cylinder side in the drawings. Further, in a direction perpendicular to the axis x (hereinafter also referred to as a radial direction), a direction toward the axis x is defined as an inner peripheral side (a direction of an arrow a in FIG. 1), and a direction away from the axis x is defined as an outer peripheral side ( The direction of arrow b in FIG. 1).

  As shown in FIG. 1, a valve stem seal 1 according to the present embodiment is formed of an annular metal ring 10 made of a metal centered on an axis x and an elastic body attached to the metal ring 10. An annular elastic body portion 20 centered on the axis x. In use, the valve stem seal 1 is fitted to an end of the valve guide 51 on the cam side A, and the valve stem 52 is inserted therethrough. The valve stem seal 1 controls the amount of lubricating oil supplied from the cam side A to the space between the valve guide 51 and the valve stem 52 while the valve guide 51 and the valve The gap between the stem 52 and the stem 52 is sealed.

  The valve guide 51 has a cylindrical shape extending in the axis x direction, and has a guide hole 53 that is a through hole extending in the axis x direction, through which the valve stem 52 is inserted so as to be able to reciprocate in the axis x direction. ing. The guide hole 53 extends between a cam-side end 54 which is an end of the valve guide 51 on the cam side A and a cylinder-side end (not shown) which is an end of the cylinder side B. An engagement groove 55, which is an annular groove, is formed on the outer peripheral surface of the valve guide 51 on the cam side end portion 54 side (one end side). The engagement groove 55 is formed, for example, on the cam-side end portion 54 side of the valve guide 51 such that the portion on the cam side A protrudes more outward than the portion on the cylinder side B.

  The elastic body of the elastic body portion 20 is formed of, for example, a rubber material such as fluoro rubber. The metal ring 10 is manufactured by, for example, press working or forging, and the elastic body portion 20 is formed by cross-linking (vulcanization) using a forming die. At the time of this cross-linking molding, the metal ring 10 is placed in a molding die, the elastic body portion 20 is adhered to the metal ring 10 by cross-linking adhesion, and the elastic body portion 20 is formed integrally with the metal ring 10. You.

  The metal ring 10 includes an annular reinforcing ring 11 centered on the axis x, and an engaging portion 12 that can engage with a valve guide 51 extending from the reinforcing ring 11. As shown in FIG. 1, the reinforcing ring portion 11 has a substantially L-shaped cross-sectional shape along the axis x (hereinafter, also referred to as a cross-sectional shape), and has a cylindrical portion extending in the axis x direction. And a flange portion 11b which is a hollow disk-shaped portion extending from the end of the cylindrical portion 11a on the cam side A toward the axis x. The cylindrical portion 11a is capable of accommodating therein a portion of the valve guide 51 on the cam side end portion 54 side, and the inner diameter of the cylindrical portion 11a is equal to the cam side end portion 54 of the valve guide 51 accommodated in the cylindrical portion 11a. It may be the same as the outer diameter of the side part, or it may be different (small or large). However, it is preferable that the valve guide 51 can be easily inserted into the cylindrical portion 11a and can be easily removed from the cylindrical portion 11a.

  As shown in FIGS. 1 and 2, the engaging portion 12 extends from the end of the cylindrical portion 11 a of the reinforcing ring portion 11 on the cylinder side B, and gradually extends from the reinforcing ring portion 11 along the axis x direction from the axis x. It has a plurality of claw portions 13 extending apart. The claw portion 13 is deformable so as to extend in the direction of the axis x as described later. Each of the claws 13 has an engagement protrusion 14 formed so as to be able to engage with a valve guide 51 protruding toward the axis x.

  The claw portion 13 is, for example, a plate-like portion extending from the end of the reinforcing ring portion 11 on the cylinder side B in the axial direction x and the outer peripheral direction, and can be in close contact with the outer peripheral surface of the valve guide 51 on the cam side end portion 54 side. Shape. Specifically, the claw portion 13 of the engagement portion 12 is formed by cutting a ring-shaped portion extending in the direction of the axis x from the reinforcing ring portion 11 along the axis x. More specifically, the claw portion 13 has a cylindrical portion around the axis x formed by extending the cylindrical portion 11a of the reinforcing ring portion 11 from the end on the cylinder side in the direction of the axis x. It is formed by being cut in parallel. Thereby, the claw portion 13 can be easily formed. In the present embodiment, the engaging portion 12 has eight claw portions 13, and the claw portion 13 is formed by an axis in which the cylindrical portion 11 a of the metal ring 10 extends in the axis x direction from the end on the cylinder side. It is formed by cutting a cylindrical part centered at x at equal intervals in the circumferential direction parallel to the axis x (eight equal parts). Each claw portion 13 has the same shape.

  Further, the engagement protrusion 14 is formed on the free end side of the claw portion 13 on the cylinder side B, and protrudes inward from an inner peripheral surface 13 a which is an inner peripheral surface of the claw portion 13. It extends in the circumferential direction on the inner peripheral surface 13a. As will be described later, the engagement protrusion 14 can be engaged with an engagement groove 55 formed on the cam-side end portion 54 of the valve guide 51 in a use state.

  Although the valve stem seal 1 according to the present embodiment has eight claws 13 as shown in FIG. 2, the number of the claws 13 is not limited to eight, but may be four or There may be six or the like. Further, the widths of the claws 13 in the circumferential direction are not equal to each other, and may have different widths. Further, the claw portions 13 may be formed in the engagement portion 12 such that a gap is formed between the claw portions 13 adjacent to each other in the use state.

  Further, as shown in FIG. 1, the claw portion 13 extends to the cylinder side B beyond the engagement protrusion 14, and in a portion on the cylinder side B relative to the engagement protrusion 14, the outer circumferential side relative to the engagement protrusion 14 A stepped portion 15 is formed which is recessed. The step portion 15 forms a space between a part of the free end side of the claw portion 13 and the outer peripheral surface of the valve guide 51 in a use state as described later.

  An annular groove 16 which is an annular groove is formed on the outer peripheral surface of the reinforcing ring portion 11 of the metal ring 10. The annular groove 16 is formed at the end on the cylinder side B to which the claw portion 13 of the cylindrical portion 11a of the reinforcing ring portion 11 is connected. The portion of the metal ring 10 where the annular groove 16 is formed is formed of metal. It is thinner than other parts of the ring 10. In the present embodiment, the annular groove 16 is formed over the entire circumference of the cylindrical portion 11a, but the annular groove 16 may be formed so as to correspond to the claw portion 13. That is, the annular groove 16 may be formed so as to extend in the circumferential direction corresponding to each claw portion 13, and may be formed over at least a part of the circumferential width of each claw portion 13. .

  The elastic body portion 20 has a seal portion 21 and a positioning protrusion 22 integrally, and has an annular shape centered on the axis x. The seal portion 21 includes an annular seal base 23 extending in the direction of the axis x, a seal lip 24 abutting on a valve stem 52 inserted as described later, and the engagement portion 12 of the metal ring 10 from the seal lip 24 (cylinder). The back pressure lip 25 abuts the valve stem 52 arranged on the side B).

  Specifically, as shown in FIG. 1, the seal lip 24 extends from the seal base 23 toward the cam side A, and the end of the cam side A has an axis x as a center on the inner peripheral side. An annular lip tip 24a is formed. The lip tip portion 24a protrudes toward the axis x, and is a wedge-shaped portion having a sectional shape protruding toward the inner peripheral side. In use, the seal lip 24 abuts the valve stem 52 at the lip tip 24a.

  A garter spring 26 is fitted on the outer peripheral side of the seal lip 24 so as to face the lip tip portion 24a. The garter spring 26 urges the seal lip 24 in the direction toward the axis x, and The lip tip 24a exerts a tightening force on the valve stem so that the valve stem 24a follows the displacement of the valve stem 52.

  As shown in FIG. 1, the back pressure lip 25 is disposed on the cylinder side B side of the seal base 23 at a distance from the seal lip 24, and extends from the cylinder side B of the seal base 23 toward the axis x. The lip. More specifically, the back pressure lip 25 is a conical cylindrical lip centered on an axis x extending from the end of the seal base 23 on the cylinder side B in the inner circumferential direction toward the cylinder side B. In use, the back pressure lip 25 abuts the valve stem 52.

  As shown in FIG. 1, the positioning projection 22 is an annular projection centered on the axis x, and extends from the seal base 23 toward the cylinder side B on the outer peripheral side of the back pressure lip 25. The positioning projection 22 comes into contact with the valve guide 51 at the cam-side end 54 (cam-side surface) when attaching the valve stem seal 1 to the valve guide 51, and when the positioning projection 22 comes into contact with the valve guide 51. The engagement portion 12 of the metal ring 10 is positioned so as to be able to engage with the valve guide 51.

  As shown in FIG. 1, the elastic body portion 20 has an annular protrusion 27 disposed between the seal lip 24 and the back pressure lip 25 in the axis x direction. The protrusion 27 is an annular protrusion that is provided on the seal base 23 side of the seal lip 24 and protrudes from the inner peripheral surface of the seal lip 24 toward the axis x. The projection 27 is a part for supporting the valve stem 52 in order to suppress the eccentricity of the valve stem 52 in a use state, and abuts on the valve stem 52. The projection 27 has at least one notch 27a, which is a portion formed by cutting out a part of the inner peripheral side (tip portion) of the projection 27. The projection 27 does not come into contact with the valve stem 52 inserted in the direction of the axis x (the valve stem 52 in a non-eccentric state) in the use state, and the valve stem 52 is eccentric from the axis x by a predetermined range or more. Alternatively, it may be formed so as to contact the valve stem 52.

  The protrusion 27 has at least one notch 27a as described above, and in the present embodiment, has four notches 27a. The four notches 27 a are formed at equal angular intervals in the circumferential direction at the protrusion 27. As described above, the projection 27 supports the valve stem 52 in the use state. However, since the notch 27a is formed, the contact surface of the projection 27 with the valve stem 52 is reduced, and The sliding resistance with respect to the valve stem 52 is reduced.

  As shown in FIG. 1, the metal ring 10 is attached to the elastic body 20 by bonding an inner circumferential end (end 11 c) of the flange 11 b of the reinforcing ring 11 to the elastic body 20. . Specifically, an inner peripheral end 11c of the flange portion 11b of the reinforcing ring portion 11 is bonded to the seal base portion 23 of the seal portion 21 in a state of being buried from the outer peripheral side. Further, the metal ring 10 is attached to the elastic body portion 20 such that the engagement portion 12 is located closer to the back pressure lip 25 and the positioning protrusion 22 than the seal base portion 23 is. Thus, the positioning protrusion 22 and the back pressure lip 25 are located closer to the cylinder side B than the flange portion 11b of the reinforcing ring portion 11 of the metal ring 10.

  Next, a method of attaching and removing the valve stem seal 1 having the above-described configuration to and from the valve guide 51 will be described.

  As shown in FIGS. 1 and 2, before the valve stem seal 1 is attached to the valve guide 51, the claw portion 13 of the engaging portion 12 of the metal ring 10 gradually moves from the reinforcing ring portion 11 along the axis x direction. It extends away from the axis x and extends from the reinforcing ring portion 11 to the outer peripheral side. In this state, when the valve stem seal 1 is fitted to the cam end 54 of the valve guide 51, that is, the cam end 54 of the valve guide 51 is inserted into the cylindrical portion 11a of the metal ring 10. Then, the positioning protrusion 22 of the elastic body portion 20 comes into contact with the cam-side end portion 54 of the valve guide 51. When the positioning protrusion 22 contacts the cam-side end portion 54 of the valve guide 51, the engaging portion 12 is positioned at a position where it can be engaged with the valve guide 51 as described later.

  In the state where the valve stem seal 1 is positioned as described above, as shown by the imaginary line in FIG. 1, the end on the cylinder side B of each claw portion 13 of the engaging portion 12 is pressed from the outer peripheral side to the inner peripheral side. Then, when the claw portion 13 is deformed from the base so that the extending direction of the claw portion 13 becomes the axis x direction, the claw portion 13 is engaged with the valve guide 51. Specifically, as shown in FIG. 3, the engagement protrusion 14 formed on the claw portion 13 engages with the engagement groove 55 formed on the cam side end portion 54 side of the valve guide 51, and 13 cannot move in the cam side A direction. in this way. When the engagement protrusion 14 of the claw portion 13 engages with the engagement groove 55 of the valve guide 51, the metal ring 10 is attached to the valve guide 51 and cannot be moved in the direction of the cam side A. It is attached to the guide 51. The engagement groove 55 of the valve guide 51 is a groove formed by projecting the portion on the cam side A in the outer peripheral direction from the portion on the cylinder side B, and the engagement protrusion 14 of the claw portion 13 is engaged with the engagement groove 55. When engaged, the engagement protrusion 14 and the engagement groove 55 are locked in the direction of the axis x (direction in which they are separated from each other). Therefore, the valve stem seal 1 is firmly attached to the valve guide 51 by the engagement of the claw portion 13 with the engagement groove 55 of the valve guide 51 at the engagement protrusion 14.

  Here, in the reinforcing ring portion 11 of the metal ring 10, the annular groove 16 is formed at the base of each claw portion 13 of the engaging portion 12 as described above, and the claw portion of the reinforcing ring portion 11 is formed. The base of 13 has a smaller radial width than the other portions. Therefore, the above-described deformation (bending) of the claw portion 13 when the engagement portion 12 is engaged with the valve guide 51 is easily performed along the annular groove 16. For mounting the valve stem seal 1, for example, a press-fitting jig is used, and the claw portion 13 is bent.

  As shown in FIG. 3, when the valve stem seal 1 is attached to the valve guide 51, the positioning protrusion 22 of the elastic body portion 20 is in contact with the cam-side end 54 of the valve guide 51. Accordingly, it is possible to suppress the lubricating liquid entering from the engagement portion between the metal ring 10 and the valve guide 51 from entering the guide hole 53 direction beyond the positioning protrusion 22. Further, the valve stem seal 1 is positioned such that the claw portion 13 can be engaged with the engagement groove 55 of the valve guide 51 by the positioning projection 22 being pressed against the cam-side end portion 54 of the valve guide 51. May be positioned at the same position. In this case, when the valve stem seal 1 is attached to the valve guide 51, the positioning protrusion 22 is pressed between the cam side end 54 of the valve guide 51 and the metal ring 10 and the cam side end 54 is pressed. Is in contact with Therefore, the sealing performance of the contact portion of the positioning projection 22 can be improved. Further, the engagement between the engagement protrusion 14 of the claw portion 13 and the engagement groove 55 of the valve guide 51 can be strengthened.

  When the valve stem seal 1 is detached from the valve guide 51 for maintenance or replacement of the valve stem seal 1, the claw portion 13 spreads before being attached (before deformation) as shown in FIGS. Return to the state. Specifically, the end of the claw portion 13 of the engaging portion 12 on the cylinder side B is pressed to the outer peripheral side, so that the end of the claw portion 13 on the cylinder side B is widened toward the outer peripheral side. Thereby, the engagement between the engagement protrusion 14 of each claw portion 13 and the engagement groove 55 of the valve guide 51 is released, and the engagement portion 12 and the valve guide 51 are released from the engaged state. When the engagement state between the engagement portion 12 and the valve guide 55 is released, the metal ring 10 can be moved from the valve guide 51 to the cam side A, and the valve stem seal 1 It becomes removable from 51.

  In the reinforcing ring portion 11 of the metal ring 10, an annular groove 16 is formed at the base of the claw portion 13 of the engaging portion 12, and the reinforcing ring portion 11 is formed in the annular groove 16 in a radial direction more than other portions. Is thinner. For this reason, the claw portion 13 is easily bent starting from the annular groove 16, and the engagement between the claw portion 13 and the valve guide 51 is easily released.

  Here, as described above, at the end of the claw portion 13 on the cylinder side B, a step portion 15 that is recessed on the outer peripheral side from the engagement protrusion 14 is formed, and as shown in FIG. In a state where 1 is attached to the valve guide 51, a space is formed between the end of the claw portion 13 on the cylinder side B and the outer peripheral surface of the valve guide 51. For this reason, when expanding each claw part 13 to the outer peripheral side as described above in order to remove the valve stem seal 1 from the valve guide 51, the claw part 13 is pushed to the outer peripheral side via the step 15 of the claw part 13. The force is easily applied to the claw portion 13.

  Thus, according to the valve stem seal 1 according to the embodiment of the present invention, the claw portion 13 can be easily bent from the annular groove 16 in the metal ring 10. Therefore, the claw portion 13 can be easily engaged with the engagement groove 55 of the valve guide 51, and the engagement between the claw portion 13 and the engagement groove 55 of the valve guide 51 can be easily released. The valve stem seal 1 can be easily attached to the valve guide 51, and can be easily removed from the valve guide 51. Therefore, when the valve stem seal 1 is removed from the valve guide 51 at the time of replacement or maintenance of the valve stem seal 1, damage to the valve guide 51 or the valve stem 52 can be suppressed. In addition, the valve stem seal 1 is attached to the valve guide 51 firmly against a force in the axis x direction by the engagement between the engagement protrusion 14 of the claw portion 13 and the engagement groove 55 of the valve guide 51 in the axis x direction. Can be. For this reason, the valve stem seal 1 can be made hard to come off from the valve guide 51 even when receiving a high back pressure.

  As described above, according to the valve stem seal 1 according to the embodiment of the present invention, the attachment to the valve guide 51 and the removal from the valve guide 51 can be facilitated.

  As described above, the preferred embodiment of the present invention has been described. However, the present invention is not limited to the valve stem seal 1 according to the above-described embodiment, but includes any concept included in the concept of the present invention and the claims. Including embodiments. In addition, the components may be appropriately selectively combined so as to achieve at least a part of the above-described problems and effects. For example, the shape, material, arrangement, size, and the like of each component in the above-described embodiment can be appropriately changed depending on the specific usage of the present invention.

1,100 Valve stem seal 10 Metal ring 11 Reinforcement ring 11a Cylindrical part 11b Flange part 11c End part 12 Engagement part 13 Claw part 13a Inner peripheral surface 14 Engagement projection 15 Step part 16 Annular groove 20, 102 Elastic body part Seal part 22 Positioning protrusion 23 Seal base 24, 103 Seal lip 24a Lip tip 25 Back pressure lip 26 Garter spring 27 Projection 27a Notch 51, 111 Valve guide 52, 110 Valve stem 53 Guide hole 54 Cam side end 55 Groove 101 Reinforcement ring x axis

Claims (5)

An annular reinforcing ring portion centered on the axis, and a metal metal ring including an engaging portion engageable with a valve guide extending from the reinforcing ring portion,
An annular elastic body portion centered on the axis formed of an elastic body attached to the reinforcing ring portion,
The elastic body portion includes a seal lip abutting on a valve stem , and a back pressure lip abutting on the valve stem disposed on the engagement portion side of the metal ring from the seal lip,
In the metal ring , the engaging portion extends from one end of the reinforcing ring portion in the axial direction, and has a plurality of claw portions that gradually extend away from the axis along the axial direction from the reinforcing ring portion. The reinforcing ring has an annular groove formed at the one end on the outer surface of the reinforcing ring,
The claw portion is deformable so as to extend in the axial direction starting from the annular groove , and each of the claw portions is formed so as to be engageable with the valve guide protruding toward the axis. A valve stem seal having a projection. 2. The valve stem seal according to claim 1 , wherein the claw portion has a stepped portion that is recessed on an outer peripheral side with respect to the engagement protrusion in a portion on a free end side with respect to the engagement protrusion . 3. The said plurality of nail | claw parts of the said engagement part are formed by cutting | disconnecting the annular part extended in the said axial direction from the said reinforcing ring part along the said axis. Hub stem seal.   The valve stem seal according to any one of claims 1 to 3, wherein the engagement protrusion of the claw portion is engageable with a groove formed on one end side of the valve guide. The elastic body portion has a positioning protrusion that is an annular protrusion extending toward the engagement portion side from the back pressure lip in the axial direction, and in a state where the positioning protrusion contacts the valve guide, The valve stem seal according to any one of claims 1 to 4, wherein the engagement portion is positioned at a position capable of engaging with the valve guide.

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