DESIGN and the material used in the construction of automotive poppet valves, particularly exhaus valves, are discussed in connection with the necessity of resistance of the valves to physical and chemical actions of wide variety. The problem of resisting these actions lends itself to mechanical and metallurgical solution. Each part of the valve-the head, the stem, and the end and tip of the stem-is discussed separately; and the design of the head is considered as it relates to the upper or combustion-chamber surface, the edge, the seat and the lower or manifold-radius portion. Provisions made for the grinding-in of the valves are shown and described.
Methods employed for maintaining the valves sufficiently cool to avoid excessive warping, pitting, scoring and the like include providing an ample valve-seat, designing the gas passage under the valve-head as nearly streamline as possible, making the valve-stem of large enough diameter to conduct the heat away rapidly, making the stem hollow and inserting cooling solution or a solid that melts at normal engine-operating temperature, inserting a high-conductive rod or tube core in the stem, and valve-guide design and bronze guides to conduct the heat away.
Special alloy metals are used as valve-insert materials to counteract stem expansion and maintain constant clearance with the tappet, and as caps or inserts for the stem tips to resist the effects of heat and hammering.
The dicussion covers a wide range of related subjects, such as the effect of the use of ethyl gasoline, the best steel to use for valves, reason for the high cost of airplane-engine valves, lubrication of the stem, valve springs and their effect, gumming and sticking, distortion of the cylinder-block, materials used for inserted valve-seats, and so forth.