CHECKING VALVE SPRINGS
See Figures 1 and 2
Place the valve spring on a flat surface next to a carpenter's square. Measure the height of the spring, and rotate the spring against the edge of the square to measure distortion. If the spring height varies (by comparison) by more than 1 / 16 inch; (1.6mm) or if the distortion exceeds 1 / 16 inch; (1.6mm), replace the spring.
Have the valve springs tested for spring pressure at the installed and compressed (installed height minus valve lift) height using a valve spring tester. Springs should be within one pound, plus or minus each other. Replace springs as necessary.
VALVE SPRING INSTALLED HEIGHT
After installing the valve spring, measure the distance between the spring mounting pad and the lower edge of the spring retainer. Compare the measurement to specifications. If the installed height is incorrect, add shim washers between the spring mounting pad and the spring. Use only washers designed for valve springs, available at most parts houses.