What is a Cylinder Liner?

Meaning | Concept | Definition:

A cylinder liner is a device that is pressed into an engine block and houses the piston. It is much harder than the engine block and prevents the piston from wearing through the cylinder bore. Typically used on aluminum engine blocks and diesel engines, the cylinder liner is pressed into position or held in place by the cylinder head.

On large engines, such as those found on diesel locomotives, the liner is part of an assembly containing a new piston, piston rings, and connecting rod and is replaced as a complete unit during scheduled maintenance or repair.

Without a cylinder liner, the cylinder head can be damaged.

In aluminum engine blocks, the block material is too soft to hold a piston. The friction of a piston moving up and down within the alloy block would soon wear out, resulting in loss of compression and severe oil consumption.

The cylinder steel liner is pressed into the engine block, and then the engine block is machined to ensure that the cylinder head contact surface is smooth and flat. By machining the engine block to receive a steel liner, the engine can run for many years without failure.

Poorly sealed gaskets can lead to engine problems, especially in the case of a poorly fitting head gasket.

The flat surface resulting from the machining of the engine block ensures a proper head gasket seal between the cylinder head and the engine block. An improperly sealed head gasket will result in engine overheating, loss of power, and the possibility of ruining the block and head.

Great care must be taken when installing a cylinder liner on an aluminum engine block, as the aluminum block will react to heat at a different rate than the steel cylinder liner. Improper fit on installation could result in a torn liner or cracked engine block.

There are also cases where a cylinder liner can be used to repair a cast iron engine block that has suffered catastrophic cylinder wall failure. Often when an engine misfires or “blows out”, the cylinder wall bears the brunt of the trauma, rendering it irreparable by drilling too far.

In this case, the block could be machined to receive a liner and then all the cylinders could be over-bored to the same size, rendering the engine serviceable again. For street vehicles, this is a viable option that typically offers the vehicle owner significant savings over the cost of a replacement engine.

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