Rocker arm and method of manufacturing the rocker arm

A method of manufacturing a rocker arm, the rocker arm comprising

• a pair of side wall sections provided with a space therebetween;
• a first connecting section and a second connecting section which connect corresponding portions near lengthwise opposite ends of the pair of side wall sections;
• and
• a pair of mutually concentric circular holes formed in the pair of side wall sections at mutually matching positions,
• wherein the first and second connecting sections have engagement sections which engage with a valve body and a rocking support member;
• the method comprising the steps of:
• (a) applying cold forging to a starting blank which is obtained by cutting a metal wire rod to a predetermined length,
• (b) making a first intermediate blank by applying cold forging to the starting blank by pressing the starting blank from lengthwise opposite the longitudinally opposed sides;
• (c) forming a run-off portion when one of the first engagement section and_the second engagement section is formed in one of step (a) and step (b), the run off portion being formed from portions which are away toward the inside in a widthwise direction from the pair of side wall sections, at least one portion being at a same position in relation to the lengthwise direction as a portion which is to form one of the first engagement section and the second engagement section;
• wherein the run-off portion is not struck by a die used in the cold forging.

A method of manufacturing a rocker arm, the rocker arm comprising

• a pair of side wall sections provided with a space therebetween;
• a first connecting section and a second connecting section which connect corresponding portions near lengthwise opposite ends of the pair of side wall sections;
• and
• a pair of mutually concentric circular holes formed in these two side wall sections at mutually matching positions,
• wherein the first and second connecting sections have engagement sections which engage with a valve body and a rocking support member,
• the method comprising the steps of:
• (a) applying cold forging to a starting blank which is obtained by cutting a metal wire rod to a predetermined length,
• (b) making an first intermediate blank by applying cold forging to the starting blank by pressing the starting blank from lengthwise opposite the longitudinally opposed sides;
• (c) forming the circular holes in the side wall sections by simultaneously forming the chamfers on the outside open end portions of the circular holes;
• (d) forming a run-off portion when one of the first engagement section and the second engagement section is formed in one of step (a) and step (b) the run off portion being formed from portions which are oriented to the inside in a widthwise direction from the pair of side wall sections, at least one portion being at a same position in relation to the lengthwise direction as a portion which is to form one of the first engagement section and the second engagement section wherein the run-off portion is not struck by a die used in the cold forcing.

A method of manufacturing a rocker arm, the rocker arm comprising

• a pair of side wall sections provided with a space therebetween;
• and
• a pair of connecting sections which connect corresponding portions near the lengthwise opposite ends of the pair of side wall sections,
• wherein the connecting sections have engagement sections which engage with a valve body and a rocking support member,
• the method comprising the steps of:
• applying a first cold forging to a starting blank which is obtained a by cutting a metal wire rod having a circular cross-section to a predetermined length,
• making a first intermediate blank with a cross-section area changed in relation to the axial direction, corresponding to a change in the cross-section area related to the lengthwise direction of the rocker arm to be obtained,
• applying at least a second cold forging to the first intermediate blank, to thereby make a second intermediate blank provided with a base which connects the pair of side wall sections and one portion pairs of the side wall sections;
• and
• applying a hole forming process for forming a circular hole in a lengthwise middle portion of the base of the second intermediate blank to make a third intermediate blank provided with a pair of connecting sections.