In engine, there is valve and the valve spring. If you have ever look at the valve spring before, then you will notice that one end has its coil closer together than the other end. So a valve spring is a kind of progressive spring. In almost all engine repair manual I read, the instruction is always say that the end of the valve spring which has closer coil should be facing down (i.e. closer to the valve). 1) Why the closer coil end must be always touching the valve? 2) What will happen if the spring is put upside down? I have search in the internet and I found that the reason for using a progressive spring as valve spring is for the dampening effect, otherwise more complex alternative approach has to be used such as an inner spring design. However, the spring as a single entity, wouldn't it performs the same regardless of how we put it? Let's be more general, imagine we have a progressive spring (not necessary the valve spring but a general progressive spring), and then this spring is used to do the normal oscillation experiment. In the first experiment, the end with closer coil is facing down. So we get a set of measurement of amplitude and frequency of oscillation. Then repeat the experiment but let the end with closer coil facing up, we get another set of measurement of amplitude and frequency of oscillation. 3) Will the first experiment result and observation identical with the second experiment? If it is not, why?