These are the largest and heaviest parts of the engine, manufactured using casting and subsequent machining. In a liquid-cooled engine, coolant passages are located around the cylinders to form a water jacket.
Rice. Aluminum cylinder block of a V8 engine with pressed dry liners.
Air-cooled engine cylinders are usually manufactured separately and have fins to increase the cooling surface area.
The bottom of the cylinder block is usually machined to fit the crankshaft main bearings into the block and to attach the oil pan. The distance between adjacent cylinders is of great importance. Increasing the distance makes it possible to increase the rigidity of the block and provide the possibility of further increasing [[Engine displacement |engine displacement]] by increasing the diameter of the cylinders (the easiest way to obtain modifications to engines of various powers). On the other hand, this leads to an increase in the overall dimensions of the engine and its weight. Recently, some automobile engine manufacturers have been producing cylinder blocks in which adjacent cylinders touch the walls (so-called Siamese blocks). This method makes it possible to obtain a fairly rigid structure with a relatively small size. The rigidity of the cylinder block largely determines the noise characteristics of the engine.
Rice. Cylinder and piston of two-stroke air-cooled engine
For a long time, the only material for making cylinder blocks was cast iron. This material is inexpensive, it has high strength and rigidity with good casting properties. In addition, the honed internal surfaces of cast iron cylinders have excellent anti-friction properties and high wear resistance. Significant disadvantages of cast iron are its large mass and low thermal conductivity. The desire of designers to create lighter engines led to the development of cylinder block designs made of aluminum alloys. Aluminum is significantly inferior to cast iron in rigidity and wear resistance, so an aluminum block must have a large number of stiffeners, and the cylinders are usually the same cast iron liners, which are inserted into the aluminum block during the assembly process, poured or pressed into it during manufacturing. If the cylinder liner is directly flushed with coolant, it is called "wet", And if not - "dry". Wet liners must have a reliable seal with the cooling cavity of the cylinder block.
Rice. Cylinder block with a “dry” liner. The section clearly shows how “dry” liners are inserted into the cylinder block and grooves made in the piston bottoms that protect the valves from touching the piston
The use of a large number of stiffeners and cast iron liners largely negates the advantages of using cylinder blocks made of aluminum alloys. The use of modern technologies in production makes it possible to manufacture lightweight “aluminum” engines in which the cylinder block does not have cast iron liners. In the working surfaces of the cylinders in aluminum blocks, an increased silicon content is electrolytically created, and then the cylinders are chemically etched to create a wear-resistant porous film of pure silicon on the working surface of the cylinders, which retains lubricant well. In addition, especially often in two-stroke engines, a layer of chromium or a silicon-nickel alloy is applied to the aluminum cylinder ( Nikasil).
Rice. Engine with aluminum block. The cylinder block of this compact six-cylinder V-twin 24-valve engine, designed for transverse installation in a vehicle, is made entirely of aluminum alloy
The rigidity of an aluminum cylinder block can be increased not only by using a large number of stiffeners, but also by using special ladder type spacers in the block. Such spacers connected to the block, in addition to significantly increasing the rigidity of the block itself, serve as a solid basis for installing the crankshaft main bearings, which increases its durability. This cylinder block design is becoming the norm in the production of gasoline engines in modern passenger cars. In the production of diesel engines, which require high block rigidity due to high loads and noise, cast iron cylinder blocks are often used.
Rice. Ladder type frame in block. Ladder-type frames replace the usual crankshaft main bearing caps in the design of modern internal combustion engines, impart high rigidity to the cylinder block and extend the life of the crankshaft
Any motor has a complex structure, each element of which is necessary to perform a specific task. One of these elements is the cylinder head.
The cylinder head is the main component in any car or motorcycle. The device is necessary to control the exhaust of gases in an internal combustion engine. By its nature, the cylinder head is a cover that covers the block itself. The cylinder head cover is made of aluminum alloys; it can also be made of cast iron. In production, the cylinder head is subjected to an artificial aging process. The number of cylinder heads directly depends on the type of internal combustion engine; if it is V-shaped, a separate head is used for each row.
The operation of the cylinder head very much depends on the degree of sealing of the head with the cylinder block. This explains the fact that the upper part of this part is slightly narrower in comparison with the lower one. The gasket is located between the head and the cylinder block itself.
Installation and fixation of the cylinder head is carried out using pins, which are designed to secure the part. Correct installation greatly influences the further operation of the cylinder head. For each vehicle, the instructions indicate its own regulations. For this reason, you should not borrow a head installation diagram from a foreign car for a domestic car. Do not forget that the pins have a certain tightening order, and the required tightening torque is indicated. To correctly install the cylinder head, a special tool is used - a torque wrench.
When installing and tightening the cylinder head, you should primarily rely on the installation instructions rather than brute physical force. If you overtighten the cylinder head, you may damage the sealing gasket, the cylinder head oil channel and other equally important components of this system. For example, a cylinder head may crack or change in size; the entire operation of the engine, and as a result, the vehicle as a whole, depends on the operation of this element.
Design Features
The design of the cylinder head is not as simple as it seems at first glance. All components of this part will be described below.
Currently, all elements of the cylinder head are made of aluminum alloys; previously, alloy cast iron was used for the same purpose. Some vehicles are still equipped with a cast iron cylinder head. This is explained by the fact that cast iron is most suitable for very high or very low temperatures. Aluminum alloys are most susceptible to deformation due to temperature changes. The dimensions of the cylinder head change during engine operation due to increased temperature.
The cylinder head consists of the following elements.
- Sealing gasket.
- Gas distribution mechanism.
- The cylinder head housing is where all the mechanisms and pipes of the cooling system, oil wires and combustion chamber are located.
- Compartments into which spark plugs are subsequently mounted.
- Gas distribution mechanism drive.
- The combustion chamber where the fuel combustion process takes place.
- There are also landing planes that make it possible to release processed gases.
Each of these elements should be described in more detail. The cylinder head valves are located in row 1, each of which is inclined to the cylinders by twenty degrees. The latest generation cars may use a slightly different cylinder head design principle, but in general, everything is approximately the same.
It is worth talking in more detail about the sealing gasket, the basis of which is reinforced asbestos. The manufacture of this element from precisely this material is explained by the high temperatures during operation of the internal combustion engine, and a lot of pressure is also exerted on the gasket. A reinforced asbestos gasket is able to ensure the tightness of all channels and engine systems.
If you disassemble the front part of this device, you can see that the gas distribution mechanism drive is located here along with the chain tensioner. The combustion chambers have close contact with the block, for this reason they are processed mechanically. The volumes of the compression chambers are somewhat smaller than the sizes of the pistons. This is explained by the fact that during operation of the internal combustion engine, at the moment the pistons are raised, this design allows the air mixtures to swirl. As a result, the combustion process itself improves.
On the left side of the cylinder head there are holes for the spark plugs; systems for supporting the lever and support washers are also mounted here. At the top of the cylinder head there is a cover that is attached to the rest of the body with bolts.
The cylinder head contains non-removable elements. The valve seats, which are necessary for the tightness of the gas distribution mechanism, also contain guide bushings. Please note that these elements were installed using pressing. That is, it is impossible to replace them at home; you will need to contact a service center or use special equipment.
Some car owners try to do cylinder head repair work on their own, but this is not recommended, otherwise there may be negative consequences.
- The cylinder head may change in shape, resulting in the sealing of the valves and combustion chamber being compromised.
- Due to improper heating, the cylinder head will become unusable.
- The formation of cracks and microcracks is possible, with which proper operation of the motor will become impossible.
Repair work on non-removable elements at home may lead to the need to purchase a new cylinder head. No one is saying that a competent specialist cannot repair one of these parts, but this is not always possible.
Diagnostics and maintenance
Sooner or later, any mechanism in a vehicle will require diagnostics and maintenance; the cylinder head is not any exception to the rule. In this matter, the main task of the vehicle owner is to periodically diagnose those elements that most often fail.
- Valves and their seals.
- Sealing gasket.
Particular attention should be paid to the gasket; if it is worn out, the working fluids may mix, which will lead to engine failure. If coolant gets into the working oil, it will bubble. Over time, this will make it impossible to start the engine. In this case, the main signal will be the temperature sensor, which will indicate the boiling of the internal combustion engine. You can also assess the situation by removing the spark plugs. Why are repairs necessary? Most often, dismantling the cylinder head cannot be avoided in the following cases.
- The height of the cylinder head has changed.
- There was a need to press out the valves and seats.
- One or more valves have stopped functioning and need to be replaced.
- The cover needs sanding.
- The sealing gasket needs to be replaced.
- It is necessary to get rid of microcracks.
If you understand what each step will lead to and have the necessary tools, you can do cylinder head repair work at home, but even the most high-tech equipment in the hands of an inexperienced owner will not help fix the problem.
If you have any questions, leave them in the comments below the article. We or our visitors will be happy to answer them
The term "short block" engine is used most often when things are really bad, and less often when you want something new. Let's explain: an engine short block is a set of an engine cylinder block and a number of engine components, which is most often required when the piston is worn out as a reason for expensive repairs. It is the short block that is an excellent alternative to buying a whole engine, since when the piston group wears out, many engine parts actually do not wear out, and they do not require replacement, so for many it makes no sense to buy a complete engine assembly, and the short block is specially designed so to include only the essential replacement components. The second case (when you want something new) is when a short block is not just an alternative to the engine assembly, but a means of improving the dynamics of the car - such a short block can have cylinders with pistons of a larger diameter.
A short block engine usually includes pistons with rings (already pressed into the cylinder block), connecting rods and a crankshaft. Short blocks always require the installation of additional internal parts, which include (but are not limited to):
- oil pump,
- oil pan,
- an exhaust manifold,
- cylinder head (cylinder head),
- gaskets
However, short block is different from short block, and the set of certain components depends on the engine model and car. Many short blocks are available with camshafts and many additional parts (including gaskets, a small number of sensors).
Short block of a 4-cylinder engine with a set of pistons, connecting rods and crankshaft
But there is also a so-called long block - this is an improved and more complete short block, which includes, in addition to what the short block is equipped with, a cylinder head, an oil pan, an exhaust manifold, a valve cover and a number of other parts . In fact, the long block is almost a complete engine.
Civil engine building is a very conservative industry. All the same crankshaft, pistons, cylinders, valves as 100 years ago. Amazing crankless, axial and other schemes do not want to be implemented, proving their impracticality. Even the Wankel engine, the big breakthrough of the sixties, is essentially a thing of the past.
All modern “innovations”, if you look closely, are just the introduction of racing technologies from fifty years ago, seasoned with cheap-to-produce electronics for more precise control of the hardware. Progress in the construction of internal combustion engines is more likely in the synergy of small changes than in global breakthroughs.
And it seems like a sin to complain. This time we won’t talk about reliability and maintainability, but the power, cleanliness and efficiency of modern engines would seem like a true miracle to a person from the seventies. What if we rewind a few more decades?
A hundred years ago, engines were still carburetor, with magneto ignition, usually low-valve or even with an “automatic” intake valve... And they didn’t even think about any supercharging. And the old, old engines did not have a part that is now its main component - the cylinder block.
Before implementing the block
The first engines had a crankcase and a cylinder (or several cylinders), but they did not have a block. You will be surprised, but the basis of the structure - the crankcase - was often leaky, the pistons and connecting rods were open to all winds, and were lubricated from an oil can using the drip method. And the word “crankcase” itself is difficult to apply to a design that preserves the relative position of the crankshaft and cylinder in the form of openwork brackets.
For stationary and marine engines, a similar scheme remains to this day, but automobile internal combustion engines still needed greater tightness. Roads have always been a source of dust, which greatly harms machinery.
The pioneer in the field of “sealing” is considered to be the company De Dion-Bouton, which in 1896 launched a motor with a cylindrical closed crankcase, inside of which a crank mechanism was located.
True, the gas distribution mechanism with its cams and pushers was still located openly - this was done for the sake of better cooling and repair. By the way, by 1900, this French company turned out to be the largest manufacturer of cars and internal combustion engines in the world, producing 3,200 engines and 400 cars, so the design had a strong influence on the development of engine building.
...and then Henry Ford appears
The first mass-produced design with a solid cylinder block still remains one of the most mass-produced cars in history. The Model T Ford, introduced in 1908, had a four-cylinder engine, with a cast-iron cylinder head, foot valves, cast-iron pistons and a cylinder block - again made of cast iron. The engine volume was quite “adult” for those times, 2.9 liters, and the power was 20 hp. With. For a long time it was considered quite a worthy indicator.
More expensive and complex designs in those years sported separate cylinders and a crankcase to which they were attached. Cylinder heads were often individual, and the entire structure of the cylinder head and the cylinder itself was attached to the crankcase with studs. After the emergence of a trend toward larger components, the crankcase often remained a separate part, but blocks of two or three cylinders were still removable.
What is the point of separating the cylinders?
The design with individual removable cylinders looks a little unusual now, but before the Second World War, despite the innovations of Henry Ford, it was one of the most common schemes. In aircraft engines and air-cooled engines, it has been preserved to this day. And the “boxer air” Porsche 911 series 993 did not have any cylinder block until 1998. So why separate the cylinders?
A cylinder in the form of a separate part is actually quite convenient. It can be made from steel or any other suitable material, such as bronze or cast iron. The inner surface can be coated with a layer of chromium or nickel-containing alloys, making it very hard if necessary. And on the outside, build up a developed jacket for air cooling. Mechanical processing of a relatively compact assembly will be accurate even on fairly simple machines, and with good fastening calculations, thermal deformations will be minimal. You can do galvanic surface treatment, since the part is small. If such a cylinder has wear or other damage, it can be removed from the engine crankcase and a new one installed.
There are also plenty of disadvantages. In addition to the higher price and high requirements for the build quality of engines with separate cylinders, a serious drawback is the low rigidity of such a design. This means increased loads and wear of the piston group. And combining the “separation principle” with water cooling is not very convenient.
Motors with separate cylinders left the mainstream a long time ago - the disadvantages outweighed them. By the mid-thirties, such designs were almost never seen in the automotive industry. A variety of combined designs - for example, with blocks of several cylinders, a common crankcase and a cylinder head - came across in small-scale luxury cars with displacement engines (you can remember the half-forgotten Delage brand), but by the end of the 30s it all died out.
Victory of all-iron construction
The design we are familiar with today has won thanks to its simplicity and low manufacturing cost. A large casting from a cheap and durable material after precise machining is still cheaper and more reliable than individual cylinders and careful assembly of the entire structure. And on lower-valve engines, the valves and camshaft are located right there in the block, which further simplifies the design.
The cooling system jacket was cast in the form of cavities in the block. For special cases, it was possible to use separate cylinder liners, but the engine on the Ford T did not have such delights. Cast iron pistons with steel compression rings worked directly against the cast iron cylinder. And by the way, the oil scraper ring in our usual form was not there; its role was played by the lower third compression ring, located below the piston pin.
This “all-cast iron” design has proven its reliability and manufacturability over many years of production. And it was adopted from Ford by such mass producers as GM for many years to come.
True, casting blocks with a large number of cylinders turned out to be a technologically difficult task, and many engines had two or three half-blocks with several cylinders in each. Thus, in-line “sixes” of the thirties sometimes had two three-cylinder semi-blocks, and in-line “eights” were even more so manufactured according to this design. For example, the most powerful Duesenberg Model J motor was made exactly this way: two half-blocks were covered with a single head.
However, by the beginning of the forties, progress made it possible to create solid blocks of this length. For example, the Chevrolet Straight-8 “Flathead” block was already solid, which reduced the load on the crankshaft.
Cast iron sleeves in a cast iron block were also a fairly good solution. High-strength alloyed chemical-resistant cast iron was more expensive than usual, and there was no point in casting an entire large block from it. But a relatively small “wet” or “dry” sleeve turned out to be a good option.
The fundamental design of motors, mastered in the pre-war years, has not changed for many decades in a row. The cylinder blocks of many modern engines are cast from gray cast iron, sometimes with high-strength inserts in the top dead center area. For example, the cast iron block has a completely modern Renault Kaptur with an F4R engine, the maintenance of which we are talking about. Cast iron is good, in particular, because a block made of it can easily be overhauled by boring cylinders of larger diameter. Unless, of course, the manufacturer produces “repair” size pistons.
True, over the years the blocks become more and more “openworked” and less massive. It’s difficult to find numbers for early blocks, but let’s take two families of motors with a difference of just over 10 years. For the GM Gen II series block of the mid-90s, the wall thickness of the motors ranged from 5 to 9 mm. The modern VW EA888 of the late 2000s already has from 3 to 5. But we are clearly getting ahead of ourselves...
Making the block lighter
Thinning the walls, which designers have been doing with all their might in recent years, is, as you understand, not the only way to reduce the weight of the block. In the 20-30s, they thought much less about saving weight and fuel than now, but the first attempts at lightening were made. And even then they thought of using aluminum.
On racing and sports cars of that era, one could find a symbiosis of an aluminum crankcase and cylinder head with cast iron cylinder blocks. Then progress in metalworking made it possible to create a more convenient version of such a symbiosis. The cylinder block remained solid, but was cast from aluminum, which reduced its weight by three to four times, including due to the better casting properties of the metal. The cylinders themselves were made in the form of cast iron sleeves, which were pressed into the block.
The cartridges were divided into “dry” and “wet”; the difference is generally clear from the name. In blocks with a dry liner, it was inserted into an aluminum cylinder (or a block was cast around it) with an interference fit, and a “wet” liner was simply fixed in the block with its lower end, and when installing the cylinder head, the cavity around it turned into a cooling jacket. The second option turned out to be more promising at that time, since it simplified casting and reduced the mass of parts. But later, increasing requirements for structural rigidity, as well as the complexity of assembling such engines, left this technology “overboard” from progress.
Dry sleeves in an aluminum block are still the most common option for manufacturing parts. And one of the most successful, because the cast iron sleeve is made of high-quality alloy cast iron, the aluminum block is rigid and light. In addition, theoretically, this design is also repairable, like cast iron blocks. After all, a worn sleeve can be “taken out” and a new one pressed in.
What's next?
The only fundamentally new technology in recent years is even lighter blocks with the spraying of an ultra-strong and ultra-thin layer on the inner surface of the cylinders. I have already written in detail about, and even about similar structures - there is no point in repeating myself. Conceptually, we have the same internal combustion engine of the 1930s. And there is every reason to believe that until the end of the “era of internal combustion,” when electric vehicles are brought to fruition, engines running on liquid hydrocarbons will remain approximately the same.
Cylinder block
The cylinder block or crankcase is the core of the engine. The main mechanisms and parts of engine systems are located on it and inside it. The cylinder block can be cast from gray cast iron (engines of ZIL-130, MA3-5335, KamAE-5320 cars) or from aluminum alloy (engines of GAZ-24 Volga, GAE-53A, etc.). A horizontal partition divides the cylinder block into upper and lower parts. In the upper plane of the block and in the horizontal partition, holes are bored for installing cylinder liners. In the cylinder, which guides the movement of the piston, the engine's working cycle occurs. The sleeves can be wet or dry. A cylinder liner is called wet if it is washed by the coolant fluid, and dry if it is not in direct contact with the coolant.
Rice. 1. Cylinder block and block head of a V-shaped engine: 1 - cylinder block; 2 - head gasket; 3 - combustion chamber; 4 - block head; 5 - cylinder liner; 6 - sealing ring; 7 - studs
The cylinders can be cast from gray cast iron together with the walls of the water jacket in the form of one block or in the form of separate sleeves installed in the block. Engines with cylinders made in the form of replaceable wet liners are easier to repair and operate (engines of GAZ-24 Volga, GAE-53A, ZIL-130, MA3-5335, KamAZ-5320, etc.).
The inner surface of the cylinder, inside which the piston moves, is called the cylinder mirror. It is carefully treated to reduce friction as it moves in the piston cylinder and rings and is often hardened to improve wear resistance and durability. The cylinder liners are installed so that the coolant does not penetrate into them or into the sump, and gases do not escape from the cylinder. It is also necessary to provide for the possibility of changing the length of the liners depending on the engine temperature. In order to fix the vertical position of the liners, they have a special collar to rest against the cylinder block and installation belts. Wet liners in the lower part are sealed with rubber rings placed in the grooves of the cylinder block (engines of the KamaE-5320 car), in the grooves of the liners (engines of the MA3-5335, ZIL-130 cars, etc.), or copper ring gaskets installed between the block and the supporting the surface of the lower belt of the liner (engines of GAZ -24 Volga, GAE -53A, etc.). The upper end of the liner protrudes above the plane of the cylinder block by 0.02-0.16 mm, which contributes to better compression of the head gasket and reliable sealing of the liner, block and cylinder head.
Rice. 2. Engine cylinder diagrams: a - without liners, but with a short insert (ZIL -157 K, GAZ -52-04 cars); b and c - with a “wet” sleeve (YAMZ-2E6 diesels and KamAZ-5320); g - with a “wet” sleeve into which a short insert is pressed (on GAZ -24 Volga, GAZ -5EA, ZIL -130, etc.); 1 - cylinder block 2 g - water jacket; 3 - insert; 4, 5 to 6 - cylinder liners; 7 - sealing rings (rubber or copper, installed under the collar)
During engine operation, the working mixture burns in the upper part of the cylinders. Combustion is accompanied by the release of oxidation products, which cause corrosion of the cylinders. To increase the wear resistance of cylinders, some engines use inserts made of anti-corrosion cast iron. They are pressed into the cylinder block (engines of ZIL-130K, GAZ-52-04 cars) or into cylinder liners (engines of GAZ-24 Volga, GAZ-bZA, ZIL-130, etc.). This complicates engine manufacturing technology. In the future, designers plan to use special metals, which will eliminate the use of inserts in cylinders.
Transverse vertical partitions inside the cylinder block, together with the front and rear walls, provide its necessary strength and rigidity. In these partitions, as well as in the front and rear walls of the block, sockets are bored out for the upper halves of the crankshaft main bearings. The lower halves of the main bearings are housed in caps attached to the block with studs or bolts.
In V-shaped engines, one of the rows of the cylinder block is slightly offset relative to the other, which is caused by the location of two connecting rods on the crankpin of the crankshaft: one for the right and the other for the left blocks. Thus, in the V-shaped engines of GAZ -53A cars, the left cylinder block is shifted forward (along the vehicle's travel) by 24 mm, and in ZIL -130 cars - by 29 mm relative to the right block. The numbering of the cylinders is indicated first for the right cylinder block (along the direction of the car), and then for the left one: the cylinder closest to the fan is number one, etc.
The cylinder with the head serves as the space where the engine's working process takes place; The cylinder walls direct the movement of the piston.
The cylinder block is the overall casting in which the cylinders are located. In-line engines have one section of the cylinder block, while V-shaped engines have two sections (right and left), united by a common crankcase. The cylinder block is manufactured together with the crankcase. This casting, called a crankcase, serves to secure and assemble all engine mechanisms and devices.
The crankcase is cast from cast iron or aluminum alloy.
In in-line engines, when making a cast iron block, the cylinders are cast along with the block. The inner working surface of the cylinders 6, carefully processed and polished, is called the cylinder mirror. Between the cylinder walls and the outer walls of the block there is a cavity 8, which is filled with water that cools the engine, and is called a water jacket.
In the case of casting the crankcase from an aluminum alloy, as well as with a cast iron block for V-shaped engines, the cylinders are made in the form of separate cast iron liners installed in the holes of the upper and lower partitions of the block. In the block, the sleeve is secured by an upper or lower collar that fits into the recesses of the block partitions, and is clamped by a head mounted on top of the block on a gasket.
The sleeve is in direct contact with the water circulating in the water jacket and is called “wet”. In this case, the sleeve is reliably sealed in the lower partition of the block using a copper or rubber ring or several rubber rings installed below in the grooves on the sleeve.
Short liners made of special wear-resistant anti-corrosion cast iron are usually pressed into the upper part of the block cylinders or liners, which are most exposed to high temperatures and the corrosive effects of exhaust gases, to increase the service life of the engine cylinders.
With a bottom valve arrangement, one side of the inline engine block has inlet and outlet ports and seats in which the valves are installed. On the same side of the block there is a chamber - a valve box, in which the parts of the gas distribution mechanism are located. The valve box is closed with one or two covers.
In the case of an overhead valve arrangement, the pushers and rods of the gas distribution mechanism are located in the side chamber of the block or both of its sections in a V-shaped design.
A timing gear cover, cast from cast iron or aluminum alloy, is attached to the front of the crankcase. A cast iron flywheel housing is attached to the rear of the crankcase. The crankshaft and camshaft supports are located in the front and rear walls of the crankcase and its internal partitions.
The upper plane of the cylinder block or each of its sections in a V-shaped design is carefully processed and a common head is installed on it, covering the cylinders from above. In the head above the cylinders there are recesses that form the combustion chambers, and there is also a water jacket that communicates with the water jacket of the block. With an overhead valve arrangement, the cylinder head also contains valve seats and cast intake and exhaust ports. The head has threaded holes for screwing in spark plugs.
The cylinder head of carburetor engines is cast from aluminum alloy. Such a head has high thermal conductivity, as a result of which the temperature of the working mixture in the engine cylinders at the end of the compression strokes decreases. This makes it possible to increase the compression ratio of the engine without the occurrence of detonation combustion of fuel during engine operation.
Rice. 3. Shapes of engine combustion chambers
The cylinder head is attached to the block with nuts on studs or bolts. A sealing gasket is installed between the block and the head, eliminating the passage of gases from the cylinders and the leakage of water from the water jacket at the junction of the head and the block. The gasket is made of asbestos cardboard lined with thin sheet steel, or asbestos cardboard impregnated with graphite with metal edging around the edges and holes. From below, a stamped steel pan is bolted to the engine crankcase flange on a sealing gasket. The plane of the crankcase connector coincides with the axis of the crankshaft or is located below it.
With a lower one-way vertical arrangement of valves, the combustion chamber of a carburetor engine is shifted to the side
valves This offset combustion chamber provides good swirl of the mixture during compression and the best conditions for its combustion. To reduce the length I of the combustion chamber and improve the combustion conditions of the working mixture, as well as to reduce the resistance to the flow of the mixture at the inlet into the cylinder with such a chamber, the arrangement of the lower valves is usually used, inclined to the cylinder axis.
With an upper single-row arrangement of valves, the combustion chamber in carburetor engines usually has a semi-wedge shape, which provides the best conditions for combustion of the working mixture. The semi-wedge combustion chamber, due to the simplicity of its shape, can be entirely machined. This makes it possible to ensure precise compliance with the volume of the combustion chambers in all cylinders and increase the uniformity of engine operation.
With both forms of the combustion chamber, part of its surface (displacer) is located close to the bottom of the piston when it is positioned in the c. m.t. Such displacers contribute to a better distribution of the volume of the compressed working mixture and reduce the possibility of detonation during combustion of the mixture.
When making the crankcase, head and other parts (camshaft gear covers, etc.) from aluminum alloys, the overall weight of the engine is significantly reduced. If removable liners are used, it is easier to manufacture crankcases and more convenient to repair cylinders when they are worn out.
In diesel engines, the gas pressure during combustion is much higher than in carburetor engines, i.e. diesel parts experience greater loads, so they are made more durable and rigid.
The cylinder block is made of cast iron, which is especially strong and rigid. This is achieved by the significant thickness of the cylinder walls and crankcase, the presence of a larger number of ribs inside the crankcase and the displacement of the crankcase parting plane significantly below the axis of the crankshaft. The engine cylinders are equipped with dry (i.e., not in direct contact with water) liners, which are inserted into the bored cylinders of the block, or wet insert liners made of special cast iron are used. Diesel cylinder heads are made of cast iron, which also makes them stronger and more rigid than those of carburetor engines.
With a high degree of compression, to obtain the smallest possible volume of the combustion chamber in diesel engines, only the upper arrangement of valves is used. In engines with direct fuel injection (YaMZ diesel engines), the head does not have recesses above the cylinders, and the combustion chamber is formed by a corresponding recess in the piston bottom.
TO category: - Engine design and operation
