Cylinder sleeves are used in engine blocks to provide a hard-wearing material for pistons and piston rings.
The block can be made of one kind of iron that’s light and easy to cast, while the sleeve uses another kind that is better able to stand up to wear and tear.
There are three main types of sleeves - dry, flanged dry, and wet.
The dry sleeve can be cast in or pressed into a new block, or used to recondition badly-worn or damaged cylinders that can’t easily be re-bored. It’s a pressed fit in its bore in the cylinder blocks. Its wall is about 2mm thick. Its outer surface is in contact with the block for its full length. Its top finishes flush with the top of the block and can hardly be seen. Once in place, dry sleeves become a permanent part of the cylinder block.
A flanged, dry sleeve is like a normal dry sleeve, but a flange at the top fits into a recess in the surface of the engine block. It’s not a tight fit and it can be replaced if it’s worn.
With a wet sleeve, the outer surface is part of the waterjacket around the cylinder. It’s called wet because it has coolant against its outer surface. This helps speed up heat transfer between the sleeve and coolant. The sleeve is sealed at the top to prevent coolant leaks. This stops coolant entering the combustion chamber, and the bottom of the crankcase. A flange at the top of the sleeve fits into a recess in the block. The lower end has 1 or 2 neoprene sealing rings.
With coolant in direct contact with the cylinder sleeve, corrosion can be a problem. It can even insulate the sleeve from the coolant, which reduces the main advantage of having a wet sleeve at all.
The walls on wet sleeves are thicker than on dry sleeves. They don’t have the same support from the block as dry sleeves so they depend on their wall thickness to stop distortion.
In diesel engines, vibration caused by combustion can cause cavitation. This damage appears similar to corrosion and it can eventually destroy the cylinder.