Airborne Flying Services of Hot Springs, Ark., developed and now offers the Valve Wizard, a set of three valve spring compressor tools for Lycoming O-235, O-290, IO/O-320, IO/O-360, AEIO-360, O ...

Here are two common valve spring compressors for use with the heads still bolted to the engine. The stamped steel compressor (top) is fast and convenient for most stock valve springs.

Andreas R. Schamel, Joachim Hammacher, Dietrich Utsch, Modeling and Measurement Techniques for Valve Spring Dynamics in High Revving Internal Combustion Engines, SAE Transactions, Vol. 102, Section 3: ...

The installed height of a valvespring is the distance from the base of the spring to the bottom of the retainer when the valve is closed. If the distance is too short the spring will be under too ...