BECAUSE of the increased engine-speed and the limitations of progress by the previous method of designing valve-springs, Packard engineers entered upon fundamental studies of valve-spring behavior and of the influence of stress range upon durability. Various theories of the dynamics of valve-spring surge were investigated, and one was found which seems to agree fairly well with the observed phenomena. Jumping of valve push-rods and spring failures that could not be explained by the static analysis of spring design are accounted for by the dynamic analysis, which serves as an improved basis for design.
Finding it impossible to design a single spring to meet the conditions, within the space limitations, a double spring with interlaced coils was designed.
Descriptions are given of the provision for mounting the ends of the springs and the methods of assembly and inspection. The dual springs are said to have been in use for more than a year on manufactured cars and on a test engine that has been operating day and night, without a single failure.