Engine block

The term "cylinder block" is often used interchangeably with "engine block". However, technically, the block of a modern engine (i.e., multiple cylinders integrated with another component) would be classified as a monobloc.

Construction

The main structure of an engine typically consists of the cylinders, coolant passages, oil galleries, crankcase, and cylinder head(s). The first production engines of the 1880s to 1920s usually used separate components for each element, which were bolted together during engine assembly. Modern engines, however, often combine many elements into a single component to reduce production costs.

The evolution from separate components to monobloc engine blocks has gradually progressed since the early 20th century. The integration of elements has relied on the development of foundry and machining techniques. For example, a practical, low-cost V8 engine was not feasible until Ford developed the methods used to build its flathead V8 engine. Other manufacturers then applied those techniques to their engines.

Cylinder block

A cylinder block is a structure that contains the cylinder, plus any cylinder sleeves and coolant passages. In the earliest decades of internal combustion engine development, monobloc cylinder construction was rare; cylinders were usually cast individually, with separate cylinder blocks produced for each cylinder. Following that, engines began to combine two or three cylinders into combined cylinder blocks, with engines combining several of these.

In early engines with multiple cylinder banks – such as V6, V8, or flat-6 engines – each bank was typically made of one or multiple separate cylinder blocks. Since the 1930s, mass production methods have developed to allow both banks of cylinders (as well as the crankcase) to be integrated into the same cylinder block.

Cylinder liners

Wet liner cylinder blocks use cylinder walls that are entirely removable and fit into the block by means of special gaskets. They are called "wet liners" because their outer sides come in direct contact with the engine's coolant. In other words, the liner is the entire cylinder wall, rather than merely a sleeve.

The advantages of wet liners are lower mass and bulk, and thanks to coolant being heated faster from a cold start, a wet liner engine has lower start-up fuel consumption and can start heating the car cabin sooner. Wet liner designs are popular with European manufacturers, most notably Renault and Peugeot, who continue to use them to the present.

Dry liner cylinder blocks use either the block's material or a discrete liner inserted into the block to form the backbone of the cylinder wall. Additional sleeves are inserted within, which remain "dry" outside, surrounded by the block's material.

For either wet or dry liner designs, the liners (or sleeves) can be replaced, potentially allowing an engine overhaul or rebuild without replacing the block itself. In reality, however, they are difficult to remove and install, and for most applications (such as most late-model cars and trucks) an engine will never undergo such a procedure in its working lifespan. It is likelier to be scrapped, with new equipment—engine or entire vehicle—replacing it.

Coolant and oil passages

Crankcase

The crankcase is the structure that houses the crankshaft. As with cylinder blocks, this is primarily an integrated component in modern engines.

Materials

Engine blocks are typically cast from either cast iron or an aluminium alloy. Aluminium blocks are much lighter and transfer heat more effectively to coolant, but iron blocks retain some advantages, such as durability and reduced thermal expansion.

Weight reductions through material selection. Presently, most of the engine blocks in mass production are gray castings. Reducing weight has resulted in using aluminum-silicon alloys more frequently for the engine block in small-displacement engines. Engine blocks of comparable design, but using Al-Si alloys, are not lighter than cast iron engine blocks in the same ratio as that for the specific weights of the materials.

In engine blocks made of gray cast iron, weight can be reduced by optimizing the structure and thin-wall casting. With this casting technique, a wall thickness of as little as about 3 mm is generally possible. In comparison, the walls of cast iron engine blocks are usually from 4.0 to 5.5 mm thick.

Using vermicular graphite cast iron (GGV), a casting material with great strength, enables weight reductions by about 30% compared to conventional casting materials such as GG 25. Weight reduction, to this extent, requires engineering for the engine block, taking into account the particular needs of the material.