Place the spring on a flat surface next to a square. Measure the height of the spring and rotate it against the edge of the square to measure distortion. If spring height varies (by comparison) by more than 1 / 16 in. (1.6mm) or if distortion exceeds 1 / 16 in. (1.6mm), replace the spring. In addition to evaluating the spring as above, test the spring pressure at the installed and compressed (installed height minus valve lift) height using a valve spring tester. Spring pressure should be within 1 lb. (0.45kg) of all other springs in either position.