ENGINE CYLINDERS AND BLOCKS

Cylinder Arrangement

Three, four, five, six, eight, or more cylinders can be found in car and light truck engines. One of three frequent arrangements for cylinders is inline, in a "V" configuration, or in opposition to one another.

Valvetrain

The crankshaft must turn twice to complete a four-stroke cycle. In order to complete one cycle, the crankshaft must make two 360° rotations, or 720° in total. Each cylinder's intake and exhaust valves open once every two revolutions. The camshaft, sometimes known as the "cam," is the "heart" of the engine and is responsible for opening the valves. The valves open at exact intervals because of the cam's off-centre lobes, which press on the components of the valvetrain.

The engine's breathing rate is managed by the camshaft. Its design may be optimized for greatest power and high-speed performance or for optimal fuel efficiency and low-speed performance. An engine created in a factory is referred to as a production engine. Variable valve timing is a feature seen in many recent automobiles because production engines strike a balance between these two issues.

Camshafts can be found in overhead cam cylinder heads or in the block. One or more camshafts are powered by the rotation of the crankshaft using one of several different combinations, such as gears, sprockets, chains, or belts. There are half as many teeth on the crank drive as there are on the cam drive since the crank must revolve twice for every time the cam turns.

Cylinder Block

The cylinder block is a complex casting that incorporates coolant jackets, sometimes known as water jackets, and oil galleries. Cast iron or aluminum is used to make cylinder blocks, which are then poured into a core formed of sand. Today's engine blocks are frequently composed of aluminum and cast around so-called sleeves, which are iron cylinder bore liners. This enables cast iron's durability and accuracy in the cylinder bore area in addition to the weight reductions offered by aluminum. Because aluminum cylinder wall surfaces may be manufactured to be extremely hard, certain aluminum blocks do not have iron sleeves.

Engine parts can be cast using a variety of techniques. The engine block's outside surface will be shaped during the sand casting process by the core, which is suspended in a container with a liner. The final block has core holes where the core was supported at various locations around the edge of the core box. Binders are used in the sand casting process to keep the sand grains together. The heat of the casting process cooks the sand when molten iron or aluminum is poured into the core box. The sand fragments when the casting cools. The final casting is then shook out, and any leftover sand is removed via the core holes.

Sand casting block

Foam is "lost" or consumed during the pour in the lost foam casting (LFC) method of casting. Since its initial LFC testing in 1982, General Motors has improved the procedure for use in casting blocks, heads, and crankshafts. Since its inception in 1990, Saturn has employed this method. Oil galleries need to be machined in the block casting when using traditional sand casting. The coolant channels and oil galleries may be cast into the component using LFC. Additionally, compared to sand casting, foam offers a casting that is more precise. There are no separation lines and the finished casting has a smoother look. Because the pattern does not have to be eliminated, as with sand castings, more elaborate castings are feasible.

Polystyrene beads, often known as disposable polystyrene beads, are used to create the LFC pattern. Beads are injected into a die to create a pattern, which is then superheated with steam to fuse the beads together and create the completed mould. A refractory coating is applied to the foam design to smooth out its surface. To enable the pouring and venting of the molten metal, gates and risers are fastened to the pattern. LFC employs dry, unbonded sand that is poured around and into the interior passageways in the design, in contrast to traditional sand casting, which uses binders to hold the sand together. The spaces around the design are completely filled with sand after it has been vibrated and compressed. The design is replaced during the pour as the molten metal vaporizes. The unbonded sand is poured out when the final casting has cooled and solidified. Unlike traditional casting sand, which needs to be disposed of, it may be used again.

Core plugs are used to seal the core holes. Although there are also expandable rubber and copper plugs available, core plugs are often composed of steel or brass. Because they don't rust, brass core plugs are superior. Because they are more expensive and because new engines are coolant-filled, which prevents corrosion, brass plugs are not utilized in new automobiles. Core plugs are also known as soft plugs, Welsh plugs, freeze plugs, and expansion plugs. On V-type blocks, cylinders are cast in two rows called left and right banks.

The cylinder banks on V8 blocks are spaced apart by a 90° angle during casting. There are either 60° or 90° between banks in V6 blocks. There are other odd engine layouts, such as the Volkswagen V6's 15°-angled bank angles. Both big block and small block engine configurations are available. 

Because they utilise less gasoline, smaller, lighter blocks are more common in passenger automobiles. The valley between the heads is covered by some intake manifolds, while other systems employ coverings and a separate intake plenum.

Long blocks are full block assemblies that comprise the whole valvetrain (cylinder heads and accompanying components).

Short Block and Long Block

Short block refers to the cylinder block assembly without the heads. The crankshaft, piston and rod assembly, and all bearings are part of the small block. On pushrod engines, the short block also houses the camshaft, timing sprockets, and timing chain.

Crankcase refers to the lowest portion of the cylinder block that is encircled by the oil pan and contains the crankshaft. The bottom end of the block has precisely aligned main bearing bore holes that serve as mounting points for the crankshaft and main bearings. Although the main bearing caps are replaceable, they must be done so in the exact same spot. All threaded holes, gasket surfaces, cylinder bores, cylinder head mounting surfaces, camshaft bore holes, and cylinder bores are automatically and precisely machined at the factory. The technician or machinist's responsibility while rebuilding is to preserve the original alignment.

The following list includes typical elements that both short and lengthy blocks share:

Oil Pan:  The component that encloses the crankcase is the oil pan, which is made of stamped sheet metal or cast aluminium. As air moves across its surface, the engine oil is cooled in a reservoir provided by the object. When an engine is removed and replaced or while driving, oil pans can occasionally be damaged. A sheet metal oil pan can occasionally be twisted to the point that the crankshaft bumps against it. When an engine is started after a rebuild, the resultant cacophony may be quite unsettling.

Flywheel:  A flywheel or flexplate is attached to the back of the crankshaft. The weight of the flywheel smooths out the power impulses of numerous cylinders and aids in lifting the crankshaft above BDC following the power stroke. When using a normal gearbox, a flywheel is utilized. Additionally, it gives the clutch something to operate on. Whenever an automated gearbox is present, a torque converter and flexplate are employed. For the starting motor's gear drive, a ring gear is mounted around the flywheel or flexplate. Inefficient starter motors can occasionally cause damage to the ring gears on flywheels and flexplates. While the engine is out of the car, replacing a flywheel ring gear or a flexplate is a very simple task.

Vibration Damper:  On V-type and in-line six-cylinder engines, the vibration damper, also known as a harmonic balancer, is positioned on the front of the crankshaft. Similar to how a tuning fork vibrates, the power impulses on the pistons cause the crankshaft to twist and untwist. The damper reduces these torsional vibrations, which, if left unchecked, might break the crankshaft. Most four-cylinder engines merely use a pulley and do not need dampers.

Crankshaft:  Depending on the model, the crankshaft might be composed of steel or cast iron. Journals are the bearing surfaces for the main and rod bearings. The crankshaft's midline, between the front and rear journals, is where the primary bearing journals are located. Through oil holes in the main bearings, oil galleries lubricate the main bearing journals. To pressurise grease into the rod bearings, holes are made in the crankshaft from the main bearing journals to the connecting rod bearing journals.

On V8 engines, rod journals, also known as crankpins, are offset by 90 degrees, 180 degrees, and 120 degrees, respectively. Some V6s feature crankpins that are offset.