In liquid-cooled piston-stroke engines the cylinder block contains the entire crank mechanism. It has to resist combustion pressures, oscillations of the crankshaft and conduct the heat rapidly to the coolant.
Although cast iron with flake graphite (grey cast iron) results in more weight, it has however good sliding qualities with aluminium pistons. In order to save weight and increase the heat conductivity, cylinder blocks are more and more built from aluminium alloys. In this case, either the cylinder must be from high-quality cast iron (see first picture) or the aluminium surface of pistons or cylinders must be worked over (see second picture). This is done via extracting the soft aluminium from the silicon crystals (ALUSIL), by galvanic coating with nickel and silicon-carbide (NIKASIL), or by using a hollow body from silicon-ceramics when casting (LOKASIL).
Since wet liners from centrifugal casting have direct contact with the coolant, they have to be sealed accordingly. If they start leaking, oil may flow into the crank housing. Dry liners, which do not have direct contact with the coolant, provide however more stability to the cylinder block. Liners manufactured from grey iron are in place either because of the better material combination with aluminum pistons or because of the possibility for easier repairing, for example for trucks.
Under normal conditions the top of the cylinder bears most of the wear and the centre of the stroke the fewest. Dry liners are being screwed off and equipped with pistons in oversize. If it is not possible to use an oversize piston any more, it is common for truck engines, and less so for cars, to drill further and establish a dry liner. Wet liners are exchanged together with the pistons. Good sealing is important. In case of lacking engine power and/or heavy oil consumption, a compression check or better a pressure loss check is advisable before repairing.
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