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An engine block is the structure which contains the cylinders, and other parts, of an internal combustion engine. In an early automotive engine, the engine block consisted of just the cylinder block, to which a separate crankcase was attached. Modern engine blocks typically have the crankcase integrated with the cylinder block as a single component. Engine blocks often also include elements such as coolant passages and oil galleries.
The term "cylinder block" is often used interchangeably with engine block, although technically the block of a modern engine (i.e. with an integrated crankcase) would be classified as a monobloc. Another common term for an engine block is simply "block".
Evolution of engine block design
The main structure of an engine (i.e. the long block, excluding any moving parts) 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 of these elements, which were bolted together during engine assembly. Modern engines, however, often combine many of these elements into a single component, in order to reduce production costs.
The evolution from separate components to an engine block integrating several elements (a monobloc engine) has been a gradual progression throughout the history of internal combustion engines. 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 techniques used to build the Ford flathead V8 engine. These techniques were then applied to other engines and manufacturers.
A cylinder block is the structure which contains the cylinder, plus any cylinder cylinder sleeves and coolant passages. In the earliest decades of internal combustion engine development, cylinders were usually cast individually, so cylinder blocks were usually produced individually for each cylinder. Following that, engines began to combine two or three cylinders into a single cylinder block, with an engine combining several of these cylinder blocks combined together.
In early engines with multiple cylinder banks — such as a V6, V8 or flat-6 engine — each bank was typically a separate cylinder block (or multiple blocks per bank). Since the 1930s, mass production methods have developed to allow both banks of cylinders to be integrated into the same cylinder block.
A wet liner cylinder block features cylinder walls that are entirely removable, which fit into the block by means of special gaskets. They are referred to as "wet liners" because their outer sides come in direct contact with the engine's coolant. In other words, the liner is the entire wall, rather than being merely a sleeve.
Advantages of wet liners are a lower mass, reduced space requirement and that the coolant liquid is heated quicker from a cold start, which reduces start-up fuel consumption and provides heating for the car cabin sooner.
Dry liner designs 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" on their outside, surrounded by the block's material.
For either wet or dry liner designs, the liners (or sleeves) can be replaced, potentially allowing overhaul or rebuild without replacement of the block itself, although this is often not a practical repair option.
An engine block which combines multiple elements is called a monobloc. Most modern engines (including cars, trucks, buses and tractors) use a monoblock design of some type, therefore few modern engines have a separate cylinder block. This has led to the term "engine block" usually implying a monobloc design and the term monobloc itself is rarely used.
Casting technology at the dawn of the internal combustion engine could reliably cast either large castings, or castings with complex internal cores to allow for water jackets, but not both simultaneously. Most early engines, particularly those with more than four cylinders, had their cylinders cast as pairs or triplets of cylinders, then bolted to a single crankcase.
As casting techniques improved, an entire cylinder block of 4, 6, or 8 cylinders could be cast as one. This was a simpler construction, thus less expensive (unit-wise) to make. For straight engines, this meant that one engine block could now comprise all the cylinders plus the crankcase. Monobloc straight fours, uncommon when the Ford Model T was introduced with one in 1908, became common during the next decade, and monobloc straight sixes followed soon after. By the mid-1920s, both were common, and the straight sixes of General Motors (along with other features that differentiated GM's various makes and models from the Model T) were prying market share away from Ford. (These were all flathead designs.) During that decade, V engines retained a separate block casting for each cylinder bank, with both bolted onto a common crankcase (itself a separate casting). For economy, some engines were designed to use identical castings for each bank, left and right.(p120) The complex ducting required for intake and exhaust was too complicated to allow the integration of the banks, except on a few rare engines, such as the Lancia 22½° narrow-angle V12 of 1919, that did manage to use a single block casting for both banks.(pp50-53) The hurdles of integrating the banks of the V for common, affordable cars were first overcome by the Ford Motor Company with its Ford flathead V-8, introduced in 1932, which was the first V-8 with a single engine block casting, putting an affordable V-8 into an affordable car for the first time.
The communal water jacket of monobloc designs permitted closer spacing between cylinders. The monobloc design also improved the mechanical stiffness of the engine against bending and the increasingly important torsional twist, as cylinder numbers, engine lengths, and power ratings increased.
Most engines made today, except some unusual V or radial engines, are a monobloc of crankcase and all cylinders. In such cases, the skirts of the cylinder banks form a crankcase area of sorts, which is still often called a crankcase despite no longer being a discrete part.
Engine blocks are normally cast from either a suitable grade of iron or an aluminium alloy. The aluminium block is much lighter in weight, and has better heat transfer to the coolant, but iron blocks retain some advantages and continue to be used by some manufacturers. Use of steel cylinder liners and bearing shells minimizes the effect of the relative softness of aluminium. Some engine designs use plasma transferred wire arc thermal spraying instead cylinder sleeves, to reduce weight. They can also be produced in compacted graphite iron (CGI) such as some diesel engines from Navistar International.
Integrated cylinder head
Light-duty consumer-grade Honda GC-family small engines use a monobloc design where the cylinder head, block, and half the crankcase share the same casting, termed 'uniblock' by Honda. One reason for this, apart from cost, is to produce an overall lower engine height. Being an air-cooled OHC design, this is possible thanks to current aluminum casting techniques and lack of complex hollow spaces for liquid cooling. The valves are vertical, which permits assembly in this confined space. On the other hand, performing basic repairs becomes so time-consuming that the engine can be considered disposable. Commercial-duty Honda GX-family engines (and their many popular knock-offs) have a more conventional design of a single crankcase and cylinder casting, with a separate cylinder head.
Honda produces many other head-block-crankcase monoblocs under several names, such as the GXV-series. They may all be externally identified by a gasket which would bisect the crankshaft on an approximately 45° angle.
Exhaust valve failure is common and, owing to the monobloc design, so labour-intensive to repair that the engine is normally discarded.
Several cars with transverse engines have used an engine block consisting of an integrated transmission and crankcase. Cars that have used this arrangement include the 1966-1973 Lamborghini Miura and several cars using the BMC A-series and E-series engines. This design often results in the engine and transmission sharing the same oil.
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