What is a Cylinder Liner? Types of Cylinder Liners and Their Functions

April 17, 2024 8 min read


An essential part of internal combustion engines is the cylinder liner, an engine liner or cylinder sleeve. It operates as a functional and protective element inside the engine’s cylinder block, giving the piston a durable, smooth surface to move on and providing structural and thermal advantages. It is essential to many automotive, industrial, and marine engines because it preserves engine durability, performance, and efficiency.

These metallic structures are thin and hollow and play a crucial role in internal combustion engines. The liner is installed so that the moving piston comes into total contact with its perfectly polished bore,  and the liner is in complete contact with the cylinder block.

Understanding the purpose of Cylinder Liners

A cylinder liner is a cylindrical part put into the engine block to provide a strong, smooth, and wear-resistant surface for the piston’s reciprocating motion. This ensures effective sealing and lubrication. It is essential for preserving engine durability and performance in industrial, marine, and automotive applications. The functions of cylinder liners are listed below:

Formation of Sliding Surface

It offers a smooth sliding surface for the piston’s reciprocating action. Cylinder liners are an important component of internal combustion engines. Piston rings can rush along the inner walls of the liner since there is less friction resistance. The inside surface of the liner develops a thin lubricating coating, further lowering frictional resistance.

Reduction of Wear

Cylinder liners for internal combustion engines have outstanding anti-galling characteristics that reduce wear on the liner, as well as the piston rings that come into contact with it. The piston rings would directly wear the cylinder block without a cylinder liner. Since the cylinder block would need to be replaced frequently in such a situation, replacing the cylinder liner is more economical than replacing the complete block. The liner’s presence lessens galling, a kind of wear brought on by adhesive forces between mating components.

Heat Transfer

The transmission of heat produced during combustion is one of the cylinder liners’ other essential roles. Wet liners help the heat flow from the combusting charge into the engine block and finally into the ambient air or coolant. Effective heat dissipation is ensured by the coolant’s role as a heat sink.


Maintaining a tight seal between the piston rings and the liner walls mainly depends on cylinder liners. The extraordinary smoothness of the inner cylinder walls is necessary for this sealing function. Consequently, it minimises charge leakage during the compression stroke and stops exhaust gasses from escaping into the crankcase during the exhaust stroke.

Withstanding Combustion

Internal combustion engines produce high pressure and temperature levels under harsh operating circumstances. Withstanding pressures of up to 25 bars and temperatures as high as 2500 degrees Celsius, the cylinder liners are made to resist these extreme circumstances. The engine’s cylinder block would be exposed to premature wear from the high heat and pressure produced during combustion if the cylinder liners were missing.

Materials Used In Cylinder Liners

Cast iron is the material of choice for cylinder liners because of its excellent damping qualities, porosity, and innate lubricating qualities. Centrifugal casting is produced with raw materials melted in an induction or oil-fired furnace. The particular application determines the ideal cylinder liner material. The different ferroalloys that are added to pig iron include:

  • Chromium

Ensures extended durability by improving liner hardness, wear resistance, and corrosion resistance.

  • Molybdenum

Withstands high temperatures and pressures and improves resistance to wear.

  • Nickel

Trace amounts of nickel improve casting quality overall, homogeneous strength distribution, and machinability.

  • Copper

Adding copper improves corrosion resistance, lowers friction, improves the pearlite structure, and offers a better sliding surface.

  • Vanadium

Reduces fragility while enhancing the liner’s hardness, durability, and micro-structure.

  • Titanium

Reduces compact graphite structures and minimises blow holes through its interaction with nitrogen to generate Titanium nitride.

  • Phosphorus

Improves cast iron’s grain structure, which improves performance.

  • Silicon

Stabilises the liner’s structural integrity and reduces shrinkage.

Types of Cylinder Liners

Dry Cylinder Liners

Wet Liners have a substantial thickness, which ranges from 3mm to 6mm. They lack the supporting structure provided by a cylinder block in comparison to dry liners and are in direct contact with the coolant. They are usually used in heavy duty engines where heat dissipation requirements are very stringent.

Finned Cylinder Liners

Finned liners find application in air-cooled engines. These liners feature exposed fins in direct contact with the open air to dissipate heat to the ambient air. They result in a more straightforward engine design but might face challenges in cooling the engine sufficiently under certain operating conditions.

Functions of Different Types of Cylinder Liners

The functions of  different types of cylinder liners are listed below:

Function of Dry Cylinder Liners

The engine block and the liner resist the pressure created due to the charge burning. No space is allowed between the cylinder block and the dry liner.

Function of Wet Cylinder Liners

In the case of wet liners, Heat Transfer takes place from the liner to the coolant directly, and the liner can also withstand the force generated during the combustion of the charge.

Function of Finned Cylinder Liners

Finned liners are typically utilised in engine applications when the engine can be sufficiently exposed to ambient air and does not need a coolant circuit.

Type of Cylinder LinerAdvantagesDisadvantages
Dry LinersDry Liners have a simple design due to the lack of water jackets and sealing grooves, and replacement is straightforward.Constructing the cylinder block in which it is installed is complex, and heat dissipation is less effective.
Wet LinersWet liners have the advantages of being very simple to manufacture, more effective in cooling, and less longitudinal stress due to the liner’s thermal expansion.Type Liner replacement is complex, and if the sealing o-rings are not installed properly, there is a risk of water leakage. They are also more expensive.
Finned LinersThey have excellent heat dissipation capabilities and are resistant to corrosion.It cannot be fitted in any mechanism that uses coolant because it is made to support an air-cooled engine.

Advantages and Disadvantages

Advantages of Cylinder Liners

  • Wear Resistance

Materials with a high degree of wear resistance, including cast iron, steel, or even sophisticated composite materials, are used to make cylinder liners.

  • Heat Dissipation:

The heat produced during combustion is assisted in dissipating by cylinder liners.

  • Bore Restoration

The cylinder may get worn down and imperfect with time, and replacing the liner provides an easy and cost-effective way to restore the bore to its original condition.

  • Decreased Friction

The friction between the piston rings and the cylinder walls is lessened by the smooth surface of cylinder liners.

  • Better Lubrication

Cylinder liners can be made with specific surface treatments and finishes for better lubrication.

  • Compatibility with Various Piston Materials

Engine designers can utilise various materials for cylinder blocks and pistons thanks to cylinder liners.

Disadvantages of Cylinder Liners

  • Increased Weight

The engine weighs more because cylinder liners are an additional component.

  • Cost

The price of producing and installing cylinder liners may raise the total cost of building or repairing an engine.

  • Diminished Cooling Efficiency

Since cylinder liners can serve as thermal insulators, there are situations when their presence can marginally impair the heat transfer efficiency from the engine’s cooling system to the combustion chamber.

  • Possibility of Liner Slippage

There is a chance of liner slippage or distortion in high-stress or high-temperature engine applications. This might impair engine performance and necessitate extra maintenance.


Cylinder liners are essential to internal combustion engines as they offer a smooth sliding surface for the piston’s reciprocating action. Piston rings may move quickly along the inner walls of the liner since there is less friction resistance.


  • How do dry cylinder liners differ from wet cylinder liners?

Dry liners are not in direct contact with the coolant, while wet liners are in direct contact with the engine coolant. Hence, wet liners are generally more effective at heat dissipation, while dry liners are more straightforward to manufacture and install.

  • What are the advantages of using finned cylinder liners?

Cylinder liners with fins are made for air cooling. Because of the increased surface area of the fins on these liners, air can circulate the cylinder to cool it, resulting in excellent heat dispersion.

  • How do cylinder liners contribute to engine performance and longevity?

Engine cylinder liners perform vital tasks such as giving pistons a smooth, wear-resistant surface, guaranteeing correct sealing, facilitating heat dissipation, and enhancing engine lifetime and performance.

  • How do cylinder liners contribute to engine performance and longevity?

Tests on diesel engines revealed that surface texturing of the cylinder liner during the mid-stroke reduced heavy-duty vehicle fuel consumption by 0.6 to 3.2%. On the test rig, the friction was reduced by 30%. Various coatings and surface treatments are utilised in engine liners to increase their performance and durability. They protect the engine block, which is a costly component, from wear and act as a protective wear gear which can be replaced easily, thus increasing engine life exponentially.

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