Liner has continuously in touch with the high temperature as compare to cylinder block, So there more chances of corrosion and the moving piston is also there due to that wear rate is also high. Due to all this reason liner should be differ from the cylinder block material. That’s why cylinder liner is made from nodular cast iron alloyed with chromium, vanadium and molybdenum.
As the time goes due to the movement of piston and sulfur deposit on liner will wear with use, and therefore may have to be replaced
Due to the very high working temperture, the liner is a hotter than the jacket. The liner will expand more and is free to expand diametrically and lengthwise. If they were cast as one piece, then unacceptable thermal stresses would be set up, causing fracture of the material.
Less risk of defects. The more complex the casting, the more difficult to produce a homogenous casting with low residual stresses.