We'll stay with the old fashioned name, although in this case, we're actually dealing with the lower section of the cylinder block. It slowly becomes a unit again, which accomodates the crankshaft. In between times, it looked as if the bearings of the piston and the crankshaft would be split into two parts.
Perhaps the recent, even more vehement demands for lightweight construction will be a force towards integration. As the most important target, the distinctly increasing cubic capacity (the keyword is: downsizing) is also coming into the equation, which brings a substantial strain on this main part of piston engine.
Indeed, the specification demands have not yet come to an end. The running-in procedure with its possibly higher fuel- and oil consumption, should nowadays, be kept to a minimum. Of course, during this procedure the losses caused by internal friction, must also be minimized. These points have to all be realised with the production costs looming in the back of the mind.
Research is being done, to achieve the excellent running quality of cast iron, and particularly cast iron vanadium using lightweight aluminium and the much lighter magnesium - which also increases the firmness. At the moment, this can of course, only be done by using much more material, nevertheless, it is responsible for a quite considerable weight reduction.
The times when cast iron sleeves were pressed into aluminium blocks is a thing of the past. Modern surface processing makes it possible to turn the cylinder sleeve walls into a hard frictional partner for the aluminium pistons. As a reward, the same thermal expansion of cylinder head- block and, especially important, the pistons is achievable. Their play can the be kept very low, even in a cold state.
Magnesium itself is not as favourable as a frictional partner for the pistons and the casting material. Just as cast iron sleeves were previously molded into aluminium, the same thing occurs nowadays with aluminium sleeves and magnesium. This however, is done under high pressure and is technically more complicated. The heat transfer between the two materials, as it was same in earlier times, is still a challenge.
Compared with the former cylinder blocks, one thing has probably been changed permanently: in place of the individually bolted bearing halves, there is now a module, which combines parts of the main bearing, stiffens and into which possible balance shafts and parts of the lubrication, including the oil-sump are integrated. 01/12