In comparison to the price of a complete engine, the cost of valve springs is very reasonable. Nevertheless, in cooperation with the other parts of the engine management they are a very important component. A broken valve spring can, particularly as far as the crank mechanism is concerned, cause very serious damage. For this reason a broken spring must be avoided at all costs. Since in the production of valve springs, the development is moving forward all the time, one is now working on the creation of a spring which is made up of several cords (strands). Here, in the event of a defect, first of all only a small part of the spring would be damaged, making a replacement possible before greater damage occurs. Moreover, with this design, the manufacturers are expecting a longer service life.
Modern engines will now hardly have valve springs made from completely round wire with a constant pitch. Instead of the linear- there is also the progressive valve spring made from oval wire and having a varying pitch, which no longer has the cylindrical shape but rather that of a truncated cone. Spring steel is fundamentally rich in carbon. The number of alloying components is low. Nowadays, instead of chrom-vanadium, an alloy of chrome-silicon and very little vanadium is used. Alloys which are as 'pure' as possible, enable a selective controlling of the build up of crystals during the cooling down process. To eliminate spring-fractures, non-metallic inclusions must be avoided at all costs. This limits the number of potential suppliers worldwide. Surface flaws are removed by selective material ablation. During the paring, either several cutting tools move over the wire simultaneously, or the complete lathe travels around the wire. In the second of the above pictures, a device can be seen with which the valves are held in the cylinder head and compressing their springs. This way, the two cone-halves which are slotted into the key-grooves can be removed from the top and the valve can be taken out from the bottom.