عربى 
A cylinder liner (also called a cylinder sleeve) is a cylindrical part inserted into the engine block. It acts like the "armor plate" inside the heart of the engine. Together with the cylinder head and piston, it forms a sealed combustion chamber where fuel burns to produce power.
Cylinder liners are used primarily for two key benefits:
-
Extended service life and easier maintenance – The inner wall of the cylinder is constantly subjected to high-temperature, high-pressure combustion gases and intense friction from the rapidly moving piston, making it prone to wear. Cylinder liners are made from more wear-resistant materials (such as alloy cast iron). When worn, only the liner needs to be replaced rather than the entire expensive engine block, significantly reducing repair costs.
-
Lightweight design and cost reduction – This allows the engine block to be made from ordinary cast iron or lighter aluminum alloys, with a durable cylinder liner inserted only in the critical area. This achieves weight reduction and cost savings while maintaining performance.
The two main types of cylinder liners
There are two types, distinguished by whether they come into direct contact with the engine coolant:
-
Dry liner – It does not have direct contact with the coolant. It has a relatively thin wall (about 1–3 mm thick). Advantages: the engine block has good rigidity and a compact structure. Disadvantages: heat dissipation is less efficient, and replacement is more difficult. Commonly used in smaller engines.
-
Wet liner – Its outer wall is in direct contact with the coolant. It has a thicker wall (about 5–9 mm thick). Advantages: excellent heat dissipation and easy replacement – in some cases, the liner can be replaced without fully removing the engine from the vehicle. Disadvantages: the block has slightly lower rigidity, and additional sealing rings are required to prevent coolant leakage. Most diesel engines use this type.
