LO 8-5 Identify and describe the configuration and construction of common cylinder block cylinder arrangements

Mid-Stop Liners
To eliminate the problems with the traditional top-stop liner flange, another liner design has emerged called a mid-stop , half-stop , or wet-dry liner (due to its appearance).

Mid-stop liners do not have a flange at the top of the liner that fits into a ledge near the block deck. Instead, a counterbore ledge is approximately halfway (or midway) down the liner Figure 49. In this area, on the ledge sits the equivalent of the liner flange, called a pilot pad . The area in which the pilot is positioned is much stronger than the block deck because it is surrounded by a larger, more rigid block structure. In fact, pilot surface and ledge breakage of a mid-stop liner is unheard of, and expansion of the pilots will not crack the block like tight and hot flanges can cause to block deck counterbores used by top-stop upper press fit liners.

FIGURE 08-49: Mid-stop liners use a steplike pilot near the liner midpoint. Instead of a top-stop flange, the liner has a pilot ledge that seals coolant in the water jacket and locates the liner in the block.

FIGURE 08-50: Mid-stop ledges and all liner counterbore surfaces need to be carefully inspected for erosion and other damage that creates coolant leak paths.

Using a mid-stop ledge also eliminates the need for O-rings to seal coolant around the liner. While a rubberlike backup seal may be used on some liner designs, more often only a bead of silicone is used to prevent leakage around the liner pilots and ledge Figure 50. Mid-stop liners can minimize engine block weight by reducing the size of coolant jackets. A narrower, single-wall cylinder block is used around the lower two-thirds of the liner because only the hotter upper third is cooled by coolant jackets. The absence of a top flange also reduces the space required, allowing the block to be made a bit shorter overall.

While every advantage seems to be there for mid-stop liners, top-stop liners have the advantage of having less distortion when installed in the block because they do not squeeze the liner in the middle like mid-stops do.