Abstract: A valve stem seal exhibits superior workability of mounting of a reinforcing ring to a valve stem guide and enables the reinforcing ring to be fixed to the valve stem guide in a stable manner. A reinforcing ring is mounted to a valve stem guide by fitting a cylindrical portion to the valve stem guide from a side opposite to an inward flange portion. The cylindrical portion includes a slit extending linearly in a circumferential direction and a locking protrusion that is provided on a side opposite to the inward flange portion with respect to the slit and that is to be locked by a locking recess formed in the valve stem guide. The locking protrusion is constituted by a curved portion that is gradually recessed radially inward from the side opposite to the inward flange portion with respect to the slit to a position that reaches the slit.

Abstract: A valve stem seal exhibits superior workability of mounting of a reinforcing ring to a valve stem guide and enables the reinforcing ring to be fixed to the valve stem guide in a stable manner. A reinforcing ring is mounted to a valve stem guide by fitting a cylindrical portion to the valve stem guide from a side opposite to an inward flange portion. The cylindrical portion includes a slit extending linearly in a circumferential direction and a locking protrusion that is provided on a side opposite to the inward flange portion with respect to the slit and that is to be locked by a locking recess formed in the valve stem guide. The locking protrusion is constituted by a curved portion that is gradually recessed radially inward from the side opposite to the inward flange portion with respect to the slit to a position that reaches the slit.

Abstract: Lip-type oil seals (10) having helical pumping ribs (40) are manufactured by preparing a molded foreproduct of the seal and by trimming a hat portion (62) to form a sharp sealing edge (32). Each of the pumping ribs (40) is configured to include a first section (50) of a uniform cross-section and a bilge-shaped second section (52). Trimming is made along a trim line (68) that intersects in between the length of the first sections (50) to ensure that a length of the first sections (52) is preserved between the sealing edge (32) and the second sections (52) regardless of the tolerance of positioning of a trimming knife. Oil seals having an improved initial static and dynamic sealing performance is obtained. The second sections (52) achieves a satisfactory pumping action even after a substantial wear has taken place.

Abstract: Lip-type oil seals (10) having helical pumping ribs (40) are manufactured by preparing a molded foreproduct of the seal and by trimming a hat portion (62) to form a sharp sealing edge (32). Each of the pumping ribs (40) is configured to include a first section (50) of a uniform cross-section and a bilge-shaped second section (52). Trimming is made along a trim line (68) that intersects in between the length of the first sections (50) to ensure that a length of the first sections (52) is preserved between the sealing edge (32) and the second sections (52) regardless of the tolerance of positioning of a trimming knife. Oil seals having an improved initial static and dynamic sealing performance is obtained. The second sections (52) achieves a satisfactory pumping action even after a substantial wear has taken place.

Abstract: Lip-type oil seals (10) having helical pumping ribs (40) are manufactured by preparing a molded foreproduct of the seal and by trimming a hat portion (62) to form a sharp sealing edge (32). Each of the pumping ribs (40) is configured to include a first section (50) of a uniform cross-section and a bilge-shaped second section (52). Trimming is made along a trim line (68) that intersects in between the length of the first sections (50) to ensure that a length of the first sections (50) is preserved between the sealing edge (32) and the second sections (52) regardless of the tolerance of positioning of a trimming knife. Oil seals having an improved initial static and dynamic sealing performance is obtained. The second sections (52) achieves a satisfactory pumping action even after a substantial wear has taken place.