Abstract: A method includes a spiral forming step causing a substantially linear elongated member, conveyed toward one side in a longitudinal direction of the elongated member by a pair of conveying rollers, to be engaged at one side in a second direction with a pressing member movable in the second direction so that a spiral body including the fixed coil part, the first movable coil part and the second movable coil part is formed from the linear elongated member. The spiral forming step is configured to control the position of the pressing member with respect to the second direction, based on a signal from a rotational speed sensor detecting the rotational speed of the conveying roller, a relationship between a position in the longitudinal direction of the elongated member that is engaged with the pressing member and the position in the circumferential direction after the spiral body is formed.

Abstract: At least a first movable coil part of a plurality of movable coil parts that is in the innermost place in the radial direction does not come into contact with both the fixed coil part, which is radially adjacent inwardly, and a second movable coil part, which is radially adjacent outwardly, at the same place in the circumferential direction while coming into contact with only one of the fixed coil part and the second movable coil part in a plurality of places that are circumferentially displaced, when the spiral spring is in an elasticity retaining state reached from a free length state by elastic deformation in the diameter-reducing direction.

Abstract: The present invention includes a spiral forming step causing a substantially liner elongated member, which is conveyed toward one side in a longitudinal direction of the elongated member by a pair of conveying rollers, to be engaged at one side in a second direction with a pressing member movable in the second direction so that a spiral body including the fixed coil part, the first movable coil part and the second movable coil part is formed from the linear elongated member. The spiral forming step is configured to control the position of the pressing member with respect to the second direction, while recognizing, based on a signal from a rotational speed sensor for detecting the rotational speed of the conveying roller, a relationship between a position in the longitudinal direction of the elongated member that is engaged with the pressing member and the position in the circumferential direction after the spiral body is formed.

Abstract: At least a first movable coil part of the plurality of movable coil parts that is in the innermost place in the radial direction does not come into contact with both the fixed coil part, which is radially adjacent on the inside, and a second movable coil part, which is radially adjacent on the outside, at the same place in the circumferential direction while coming into contact with only one of the fixed coil part and the second movable coil part in a plurality of places that are circumferentially displaced, when the spiral spring is in an elasticity retaining state reached from a free length state by elastic deformation in the diameter-reducing direction.

Abstract: A sealing region where a valve seat and an outer peripheral surface of a enlarged diameter portion of a flare portion are contacted to each other is configured so that an end on a side opposite a combustion chamber is positioned at a position same as or on a side away from the combustion chamber than an end on a side close to the combustion chamber of a connecting region where a lid member and an inner peripheral surface of the enlarged diameter portion are connected with respect to the axis line direction.

Abstract: A sealing region where a valve seat and an outer peripheral surface of a enlarged diameter portion of a flare portion are contacted to each other is configured so that an end on a side opposite a combustion chamber is positioned at a position same as or on a side away from the combustion chamber than an end on a side close to the combustion chamber of a connecting region where a lid member and an inner peripheral surface of the enlarged diameter portion are connected with respect to the axis line direction.

Abstract: There is provided a valve assembly including: a valve attached to a cylinder head in a movable manner along its axial line direction so as to selectively fluidly connect or close between a combustion chamber and a gas line; a plate-like holding member provided at the valve in a relatively immovable manner along the axial line direction; and a coil spring externally inserted around the valve in a state where its proximal end is directly or indirectly engaged to an external surface of the cylinder head, the coil spring being configured so that its distal end has a diameter smaller than that of the proximal end, wherein the holding member has an engaging surface facing one side along the axial line direction to hold the distal end of the coil spring.

Abstract: Hard metal particles having hardness which is lower than the hardness of a nitrided outermost layer of a spring and in the range of Hv 500 to 800 and a diameter of 500 to 900 &mgr;m are protected against the nitrided surface of the spring at a velocity of 40 to 90 m/sec to prevent generation of a microcrack in the surface layer and provide a compression residual stress comparatively deep inside the spring. Against the resultant spring surface, a number of fine metal particles having a mean diameter of all particles of 80 &mgr;m or less, a mean diameter of each particle in the range between 10 &mgr;m inclusive and less than 100 &mgr;m, a spherical or near spherical shape with no square portions, a specific gravity of 7.0 to 9.0, and hardness which falls in the range between Hv 600 and Hv 1100 inclusive and is equal to or less than the hardness of the outermost surface layer of the spring after nitriding, at a velocity of 50 to 190 m/sec.

Abstract: A sheet of strip material of metal is coiled into a ring-like member, with a broader surface thereof being oriented in a radial direction. Opposite ends of the sheet of strip material are connected together by a joint. The joint includes a concave portion and a convex portion which are adapted to be engaged with each other against a repulsive force in a circumferential direction. The ring-like member is formed, on the inner periphery thereof, with teeth for engagement with a gear of a transmission, thereby producing a friction plate.