In a motorcycle engine, the cylinder barrel (often simply called the cylinder) is a crucial component that forms the main chamber where combustion happens.
Note – The term ‘combustion’ refers to the explosion that occurs when the fuel/air mixture is ignited by the spark plug.
The cylinder barrel sits between the cylinder head and the crankcase (see pic below).
The above pictures show the cylinder barrel from a twin cylinder Kawasaki ER5 (bottom image) and the location of the barrel in the engine (top image).
The functions of a cylinder barrel are:
- Housing the Piston(s): Cylinders provide a precisely machined, cylindrical space within which the piston moves up and down during the engine’s cycles.
- Forming the Combustion Chamber: Along with the cylinder head and the top of the piston, the cylinder barrel encloses the combustion chamber where the air-fuel mixture is ignited and burned, generating power.
- Containing Combustion Pressure: The cylinder barrel must be strong enough to withstand the immense pressures and temperatures created by the combustion process. It’s typically made from durable materials like aluminum or cast iron, often with wear-resistant coatings (like Nikasil) on the inner surface.
The barrel ensures a tight seal with the piston rings to maintain proper compression, which is vital for engine efficiency. - Guiding Piston Movement: The smooth, precisely bored inner surface of the cylinder barrel ensures that the piston moves linearly and efficiently, minimizing friction and wear. Piston rings on the piston ride against this surface (on a thin film of oil) to create a seal and transfer heat.
- Facilitating Heat Dissipation: Engines generate a lot of heat. The cylinder barrel absorbs and dissipates heat from combustion, often aided by cooling fins or liquid cooling systems.
- Providing Mounting Points: The cylinder barrel connects to the crankcase (which houses the crankshaft) and the cylinder head, forming the complete engine assembly.
4 Stroke, liquid cooled, inline 4 cylinder barrel from a Kawasaki ZXR750.
2 Stroke, air cooled single cylinder barrel from a Honda SGX50 moped.
Cylinder barrels are often made from cast iron or aluminum alloy with a hardened liner for durability.
Modern barrels may feature coatings or sleeves to reduce friction and wear.
A sleeve in an engine cylinder barrel (also called a cylinder liner) is a replaceable metal insert that forms the inner surface of the cylinder where the piston moves.
It’s a clever solution for durability, repair, and performance tuning
Cylinder barrel mounted on the crankcase showing the pistons.
Bottom of a motorcycle cylinder barrel showing the sleeves that go into the crankcase.
Inside of a motorcycle cylinder barrel.
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