Spring Surge - Catastrophe or Not?
If you search the internet for "valve spring surge", you will find several sites with the same explanation, i.e. same exact words and in some cases the same misspelled words. Some of these sites belong to major performance camshaft companies. Here is the popular explanation of spring surge:
factor which causes unpredictable valve spring behavior at high
reciprocating frequencies. It's caused by the inertia effect of the
individual coils of the valve spring. At certain critical engine
speeds, the vibrations caused by the cam movement excite the natural
frequency characteristics of the valve spring and this surge effect
substantially reduces the available static spring load. In other
words, these inertia forces oppose the valve spring tension at
critical speeds. "
This explanation is grossly misleading. First of all, there is nothing unpredictable or mysterious about the spring's behavior. Secondly, the spring is always vibrating at its natural frequency, not just at critical engine speeds. The spring force oscillates about the static force, sometimes greater and sometimes less. The force does not always oppose the valve spring tension. In the 1930's spring surge was thought to be the dominate cause of cam and lifter separation, i.e. valve toss or valve float. Since the early 1950's it has been known that the other components of the valve train are more important, i.e. pushrods stiffness, etc. Study our page on Valve Train Dynamics for a better understanding of this subject.
Here are some cool videos of vibrating valve springs. The spring with few coils has a much higher natural frequency than the one with many coils. For many years it has been known that only high natural frequency springs (low mass) should be used for automotive valve trains (see Turkish (1946)).