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

1.5. Wet Sleeve Blocks

Wet Sleeve Blocks

A wet sleeve block is designed with a number of large holes or cavities into which the cylinder sleeves are inserted. Wet sleeves are made from alloyed ductile iron that is centrifugally cast and induction hardened. The walls of these liners are thick and strong enough to withstand the heat loads and combustion forces in high horsepower engines that may appear to be better handled by a parent bore block Figure 40. Coolant has direct contact with the outside of the sleeve, and there is no mechanical support like a dry sleeve has with its surrounding block. Machined surfaces inside the block structure provide points to clamp, locate, and center the wet liner in the block. Depending on the type of wet liner, O-rings, crevice seals, or a combination of room temperature vulcanizing (RTV) silicone and narrow metal-to-metal contact points are used to seal leakage from block passages circulating coolant around the liner Figure 41. O-rings prevent coolant leakage from the water jackets and into the oil pan in blocks with top- and bottom-stop–type liners.

FIGURE 08-40: Nomenclature for a top-stop–type liner that has a sealing flange at the top of the sleeve.

FIGURE 08-41: A crevice seal near the top of this flangeless mid-stop liner seals coolant from leaking onto the block deck. Silicone seals the lower pilot pad surface.

The major advantage of wet sleeve liners is the direct contact of coolant with the sleeve, which enables rapid heat transfer from the cylinder to the coolant. One or two machined reliefs on the outside surface may help remove heat from near the top piston ring to prevent carbon buildup on the upper third of the liner. Worn or damaged sleeves are easily removed, and new ones are installed during engine rebuilding to restore the cylinders to original specifications.

Three types of wet liners commonly used today are mid-stop, bottom-stop, and top-stop sleeves. Top-stop liners are the older, more traditional type of sleeve with a flange at the top that locates, centres, and is used to transmit clamping force to the liner in the cylinder block when the cylinder head is placed over the top of the liner. Mid-stop and full-stop liners are a more recent innovation, both showing up in the 1980s to solve common problems with top-stop liners. Mid-stop liners are used in new lighter-weight block designs while heavier full- or bottom-stop liners are used in high horsepower HD engines, which require the longest, trouble-free service and best sealing performance to prevent coolant leaks.

The major disadvantages of wet sleeve liners are the problems associated with preventing internal engine coolant leaks. The O-ring seal (if used) at the lower part of the liner barrel can deteriorate and leak coolant into the lubrication oil. Some engines have an external weep hole to drain the coolant that has leaked past O-rings and prevent it from entering the oil pan Figure 42. Liner vibration, caused by combustion forces, can amplify the effects of cavitation erosion, which is the perforation of the cylinder or liner wall. Cavitation produces pinholes that can completely perforate the sleeve, allowing coolant to enter the cylinder or combustion gases to enter and pressurize the cooling system. Greater attention to maintenance of the cooling system is required in wet sleeve engines to prevent cavitation. Another problem with using replaceable sleeves is ensuring that liner protrusion above the block deck is within specification and even across all cylinders. All liners require some protrusion to allow the cylinder head to transmit clamping force to the liner when in place, but without correct protrusion, combustion gases will leak past the top of the liner and into the coolant. Because the cylinder head cannot properly squeeze the head gasket if liner protrusions are incorrect, the head gaskets will also leak. Insufficient liner protrusion can allow poorly clamped liners to move. Too much cylinder head clamping force on a liner with excessive protrusion can warp the cylinder head and result in a cracked liner, cracked liner counterbores, or cracked cylinder head.

FIGURE 08-42: Detroit Series 60 engines have weep holes to drain coolant that may leak past damaged liner O-rings to the outside of the block. The weep hole prevents coolant from entering the oil pan.