on all valve springs should measure within 10 pounds for use in a
high-performance engine. Every spring must be tested, even brand new ones.
stacking shims. Always stack thin shims below thick ones to avoid
crushing the thin shims.
general, you can figure that springs which have run for more than six
months in a passenger car will not be usable for an engine which is
to be turned to maximum Specification RPM.
steel retainers are recommended whenever the engine is to be driven
at high RPM over an extended period of time such as in sports racing
or dual-purpose cars.
retainers are used they should be inspected and replaced periodically.