Cylinder Block (Engine Block)

Blocks are cast iron or aluminium. Aluminium blocks often have iron cylinder liners or special coatings on the cylinder walls to resist wear. The block also contains coolant jackets around the cylinders, oil galleries and mounting points for the oil pump, water pump and other parts.

Engines are named after the arrangement of cylinders in the block: inline (straight), V-shaped or horizontally opposed (boxer). The block design largely decides the engine’s length, width and balance.

The pistons slide in the cylinders, the crankshaft turns in the main bearings at the bottom of the block, and the cylinder head closes the top. The oil sump is bolted underneath.

A cracked block, often after frost with too little antifreeze or after severe overheating, can leak coolant or oil. Correct coolant concentration protects the block against freezing. Freeze plugs (core plugs) in the side of the block can corrode and leak coolant over time; they are a common, inexpensive repair when accessible.