There are three main types of motorcycle valve train operation – desmodromic, bucket and shim, and finger rockers (finger followers).
The desmodromic system is synonymous with Ducati, but inline-four sportsbike manufacturers are split on using either the bucket and shim system, or a finger rocker system – as used on the new Suzuki GSX-R1000.
In a bucket and shim system the valve’s stem is covered by a metal bucket. When the cam’s lobe turns it pushes on this bucket, which opens the valve against the valve spring.
In a finger rocker system, the cam’s lobe instead activates a rocker arm, which pushes directly on to the top of the valve’s stem (through a shim) to open the valve. In theory, a rocker system performs better as it is about 50% lighter than a bucket and shim system and has less float, making it more accurate at high revs and therefore better suited to a sportsbike engine. By reducing the weight, you can reduce the force needed to open and close the valve, and have a faster revving engine with reduced friction and increased valve response.