- I know that there are two-stroke and four-stroke engines, but I have no idea the difference between them. And they also say - "internal combustion engine". Is it the same or something completely different?

To make our further reasoning more understandable, let's first agree on terminology, at least on basic concepts.
An internal combustion engine (ICE) is a mechanical device in which the chemical energy of the burning fuel is converted into thermal energy, and then into mechanical energy. Fuel combustion takes place directly inside the engine, in the so-called combustion chamber formed by the cylinder and its head.

Working cycle is called a set of work processes that occur sequentially in a cylinder. There are five such processes: intake, compression, combustion, expansion and release.
Piston - a part of the engine that perceives the pressure of gases formed during the combustion of fuel, and transfers this pressure through the piston pin and connecting rod to the crankshaft.
Cylinder - the part inside which the piston moves. The inner surface of the cylinder is a guide for the piston, the outer surface is used to remove heat.
Top dead center (TDC) - the uppermost position of the piston.
Bottom dead center (BDC) - extreme lower position of the piston.
Clock (or move) - movement of the piston from one extreme position to another. In one cycle, the crankshaft turns 180 ° (half a turn).
Cylinder displacement - the volume released by the piston when it moves from TDC to BDC. The working volume is measured in cubic centimeters. For a single-cylinder engine, the displacement of one cylinder is also the displacement of the engine. For multi-cylinder engines, the working volume is defined as the sum of the working volumes of the cylinders. (Sometimes the working volume is called the displacement). In the formulas, the working volume is denoted by Vh;
Combustion chamber volume is the volume above the piston when it is at TDC. It is designated Vc.
Full cylinder called the sum of the working volume Vh and the volume of the combustion chamber Vc.
Compression ratio shows how many times the volume of the working mixture in the cylinder decreases when the piston moves from BDC to TDC.
Compression ratio (E) - the ratio of the total volume of the cylinder Va to the volume of the combustion chamber Vc
Two-stroke engine - an internal combustion engine, in which a full working cycle occurs in two strokes or, which is the same thing, in one revolution of the crankshaft.
Four-stroke engine - the same thing, but a full working cycle occurs in four strokes, that is, in two full revolutions of the crankshaft.
It is clear that these are not all the terms that we would come across in the future. And therefore, as necessary, we will explain more and more new concepts. In the meantime, this is enough to move on to the main thing: to consider the work processes and understand the engine structure.

Work cycle

We will start our consideration with a four-stroke engine - this makes it easier to understand the processes.
The first downward stroke of the piston is used to inject into the cylinder a combustible mixture consisting of fuel vapors and air in a certain proportion. The fuel mixture enters through the open intake valve. This is the intake stroke.
When the piston reaches BDC, the intake valve will close and the piston, moving in the opposite direction, will begin to compress the mixture in a compression stroke. When compressed, the mixture is heated and actively mixed.

At TDC, the mixture is ignited and burned. In this case, the volume of gases increases many times, the pressure in the combustion chamber increases. Under the action of this pressure, the piston begins to move downward, an expansion stroke occurs - the only useful working stroke.
When the piston is at BDC, the exhaust valve opens and the exhaust gases begin to escape into the atmosphere. The piston moving towards TDC actively displaces them - the exhaust stroke occurs.
Then the whole cycle is repeated.
In the operating cycle we have considered, for ease of perception, we assumed that the inlet valve opens when the piston is at TDC, and the exhaust valve opens when the piston is at BDC. In fact, in a real engine, everything is much more complicated.

Judge for yourself - after all, a valve cannot open instantly. It takes some time to open it completely, as well as to close it.
Therefore, the intake valve begins to open even before the piston reaches TDC - this is called intake advance. Accordingly, it closes after the piston arrives at BDC (intake lag).
The same thing happens with the exhaust valve: it opens before the piston arrives at BDC (release advance) and closes after TDC (release delay).
Valve opening periods - usually measured in degrees of crankshaft rotation - are called camshaft timing. Using this term now, we can say that the opening of the valves, ahead of and. closing with a delay increases the duration of the phases (expands the phases). As a result, filling the cylinder with a combustible mixture and cleaning it from exhaust gases is improved, and engine power is increased.
For clarity, it is customary to depict the phases in the form of a circular diagram (Fig. 22). Looking at it, Even an untrained viewer will see that there are periods when both valves are simultaneously open. These periods are commonly referred to as valve overlap. At this time, two processes take place at once: charging the cylinder with a fresh mixture and cleaning it from exhaust gases. On the one hand, this is bad: a part of the fresh charge literally "flies into the pipe." On the other hand, this improves the quality of the fresh charge and, therefore, combustion, therefore, increases the engine power.

1-inlet; 2 - compression; 3 - working stroke; 4 - release; 5 - intake lead; 6 - valve overlap; 7 - delayed release; 8 - advance of release; 9 - intake lag.

For the same reasons for increasing the power, the working mixture in the combustion chamber should obviously be ignited not at the moment the piston arrives, at TDC, but much earlier (after all, combustion is a process that also requires time). And not just "earlier", but in such a way that the beginning of the working stroke coincides with the pressure peak above the piston. This timing of the ignition timing is strictly individual for each engine. The ease of starting, the developed power and fuel efficiency of the engine depend on its value.

- In a four-stroke engine, everything is simple: valves open and close, mixture and gases are injected and released. But there are no valves in a two-stroke motor, and it also works. How so?
True, the main difference between a two-stroke engine is precisely that it has no valves. But the gas distribution process here follows the same laws. Only "in charge" of all this ... the piston. Another difference is that the workflow is
emanates not only above the piston, as in a four-stroke engine, but also under the piston, in the so-called crank chamber, which in
this connection is made sealed. And the third difference is in the design of the cylinder and head.

If a four-stroke engine has a very simple cylinder and a complex head (as a rule, valves are located in it), then a two-stroke engine has the opposite: the cylinder walls have windows and channels of complex configuration, and the head is simple.
What caused these differences, we will understand when we consider how the workflow proceeds in a two-stroke.
So the piston moves up. As soon as its upper edge covers the left purge channel connecting the cylinder to the crank chamber, a vacuum begins to form in the crankcase under the piston. While the right exhaust port is still open, the cylinder is vented and purged above the piston. But as soon as the upper edge of the piston closes this channel too, compression begins.
Continuing to move up, the piston with its lower edge will open the right inlet channel, and fresh fuel mixture from the carburetor will begin to flow into the crank chamber, into the cavity under the piston. Intake starts.
At the moment when the piston approaches TDC by a distance corresponding to the ignition advance (you already know about this), the spark discharge will ignite the mixture compressed in the combustion chamber. The resulting hot gases, striving to expand, will force the piston, which has passed TDC by inertia, to rush down. A working stroke will occur.

1 - crankcase inlet; 2 - compression in the crankcase; 3 - blowdown; 4 - release; 5 - compression in the cylinder; 6 - working stroke.

When the lower edge of the piston covers the intake port, compression begins in the crank chamber (it is called preliminary). The pressure under the piston will rise to 1.25-1.5 kg / cm 2.
When the upper edge of the piston head, still going down, opens the exhaust port, the exhaust gases that have retained sufficient pressure will rush into the exhaust system. Release starts.
By the time the pressure above the piston becomes almost equal to atmospheric pressure, the piston head will also open the left purge port. The combustible mixture, previously compressed in the crank chamber, will go through the purge channel into the cylinder and fill it, displacing the exhaust gases and partially mixing with them. In this case, part of the fresh charge, of course, will fly out into the outlet window. (This is called "direct discharge"). Purge occurs.
It will end when the piston that has passed the BDC starts moving upward and closes the purge port. The release will continue until the outlet window is closed.
If you try to build the valve timing diagram already familiar to us, you will have to show two processes simultaneously: one that occurs above the piston, in the cylinder, and the other, proceeding under it, in the crank chamber. The result is two diagrams, two rings. The inner one usually depicts the processes in the crankcase, the outer one - in the cylinder.

The diagrams, of course, have absolutely symmetrical valve timing.
- If in a two-stroke engine the working stroke occurs twice as often as in a four-stroke, then the power with the same working volume should be twice as much? Or am I not Understanding something?
Well, of course, it should be that way. In theory. But in practice it turns out differently.
Despite all the tricks of the designers, the cylinders of two-stroke engines are still poorly cleaned of exhaust gases. As a result, less fresh mixture gets into them, which means that the combustion process is worse.
In addition, some of the fresh mixture has time to jump out into the outlet window without having worked at all (remember the "direct discharge"?). And this circumstance alone increases fuel consumption by 20-30%. And there is also a "back blowout" in the carburetor! On motorcycles from the 50s and 60s, which had simple mesh air filters, the losses from backflow were also noticeable - up to 25% ...
In short, there is no double gain in power, no matter how hard you try. Moreover, in terms of toxicity, the "two-stroke" is clearly dirtier than its four-stroke rival.
Here the following question could be asked: "Why then ..?" It is not in my mail, but it is implied ever since the Scottish engineer Dugald Clerk in 1877 created a two-stroke engine so controversial, with many defects - and has not given up for more than a century. Therefore, we will answer.
Then, that the two-stroke is much simpler in design. Easier to manufacture. More reliable. Easier to operate. And cheaper. Agree - not so little. And if we also take into account that two-stroke engines are also constantly being improved (according to the latest information, the Australian company "Orbital" has developed a new principle of blowing a two-stroke engine, which brings this engine on a par with the best four-stroke models in terms of fuel efficiency and power), then between different motors, lasting more than one decade, may never end.

Cylinder-piston group and crank mechanism

If someone got goosebumps from this long and slightly abstruse name, then it's in vain. In fact, the "group" includes only the cylinder and the piston, and the "mechanism" unites only two units: the connecting rod and the crankshaft.
The cylinder is one of the main engine parts. The inner surface of the cylinder serves as a guide for the piston, and heat is dissipated through the outer surface. The cylinder of a four-stroke engine is the simplest. It is usually made from special cast iron. The inner surface, "mirror", is processed to high precision and cleanliness. Moreover, with the help of a special technology, a grid of micro-grooves is applied to this surface, which retain the lubricant and extend the life of the cylinder.
If the engine is cooled by the oncoming oncoming air flow, then the outer surface of the cylinder is equipped with developed fins that improve heat dissipation. If the cooling is liquid, a "jacket" is arranged around the cylinder in which the liquid circulates.
At the bottom of the cylinder there is a flange for attachment to the engine crankcase; at the top - studs for attaching the head.
This is, of course, only a general primitive scheme. In fact, there are a great many designs. Every motorcycle has a different cylinder design.
For example, cast iron, which works well for abrasion and promises durability, is not suitable for a modern engine - the cylinders would be too heavy. That is why the engineers came up with a "layered" version: only the inner thin-walled sleeve is made of cast iron, and the outer jacket is made of aluminum. And it turned out very cool. After all, aluminum has excellent thermal conductivity. And this is exactly what is required of the shirt.
The cylinder of a two-stroke engine is much more complex. As you remember, it has channels at different heights: inlet, outlet and purge. Moreover, there can be several purging channels.
Since, for reasons of weight reduction, the cylinders of two-stroke engines are also often made flaky, the windows in the sleeve must very closely match the windows in the shirt: if there is no such coincidence, the flow of working processes will sharply deteriorate, the motorcycle will lose power and efficiency. Therefore, athletes using two-stroke engines often manually polish the channels and give the leading and trailing edges a special shape that ensures the best flow of the combustible mixture.
The most serious attention has been paid to the blowing of two-stroke engines at all times. The exit of the channels into the cylinder was built at a strictly defined angle, the width and height of the windows were carefully calculated. Sometimes, for better swirling of the air-fuel mixture, a special comb-reflector, a deflector, was even arranged on the piston head. And the types of blowdowns received special names: transverse, reciprocating-loop, three-channel, cruciform, etc. We will not dwell on this. For you beginner motorcyclists, this is enough to understand the importance of purging for a two-stroke engine. And those who want to understand this deeper will find other books.

- I read that there are two-cylinder engines with a volume of only 125 cc. and there are also single-cylinder with a "pot" of 600 "cubes". Why is that?
Since its inception and for many, many years, the motorcycle engine has been predominantly single-cylinder. Is that in the class of 750 cm 3 and above, the designers supplied it with a pair of cylinders. And even then it was partly reluctant: they had to reckon with the fact that not every driver is physically able to overcome the resistance of the mixture, compressed in such a volume, and turn the crankshaft at start-up.
Single-cylinder motors, both two-stroke and four-stroke, are still built in all countries of the world and are installed on motorcycles in cases where simplicity of the device, reliability and low cost are obviously the main qualities.
These are mainly motors of small cubic capacity, with a working volume of up to 100-125 cm 3.
However, in recent years, a whole generation of single-cylinder 600cc motorcycles has appeared abroad, such as the Yamaha SRZ 660, Suzuki LS 650P, KTM 620 EGS, Honda XR 650L and the like. What is causing this? To figure it out, let's start from the stove.
It is known that a single-cylinder engine has many congenital defects. The main ones are imbalance, uneven torque, a tendency to vibrations at high speeds, and the intensity of the thermal regime. Previously, with the comparatively slow speed of the motors, these shortcomings were not so striking and could be tolerated. With the growth of capacity, the situation began to worsen. And over time, there was clearly a tendency to increase the number of cylinders. As a rule, engines from 250 cm3 and above already have two or more cylinders. This fragmentation of the working volume made it possible to significantly increase the liter capacity by increasing the speed and compression ratio.
It is calculated, however, that it is possible to reduce the volume of one cylinder and increase their number up to a certain limit. Such a limit in terms of volume is 62 cm 3 and in terms of number - eight. As an example, we can name the once famous four-stroke four-cylinder 350cc engine of the Vostok racing motorcycle (C-364) or the four-stroke eight-cylinder (!) 500cc engine of the Italian Guzzi racing motorcycle. A further increase in the number of cylinders is faced with almost insurmountable layout difficulties and can be justified only in the case of a single or piece, in extreme cases, execution. For serial motorcycles, two-, three- and four-cylinder engines are being built.
You don't need to have a rich imagination to realize that making a single-cylinder 350cc engine is much easier and cheaper than a four-cylinder of the same volume.
But not only simplicity and reliability explains the appearance in the West of a real wave of "big pots".
The fact is that the large-displacement single-cylinder engine is equipped with a massive flywheel to smooth out pulsations, which provides excellent torque uniformity at very low revs. For a long time this good quality was completely destroyed by the monstrous vibrations inherent in such a motor. But after they learned to deal with this trouble with the help of special balancing shafts, nothing could prevent the widespread use of single-cylinder engines of large cubic capacity.
And then it turned out that there is no better way to "flash" city traffic jams than a special motorcycle: narrow, easy to control, powerful, capable of dynamically accelerating, and, if necessary, dragging along in the stream at the speed of a pedestrian. Such motorcycles are called urban "enduro", and the single-cylinder 600-cc engines were ideal for them: narrow, powerful, having the necessary characteristics.
In general, we can talk about cylinders for a very long time - after all, their number and location are always indicated as one of the first and most important characteristics of a motorcycle.
But we are forced to move on: our road is long, and we are only at the very beginning!
The cylinder head of most modern two-stroke engines is cast from an aluminum alloy. Its outer surface in the case of natural cooling is strongly ribbed. Inside is a compression chamber, or, as it is more commonly called, a combustion chamber.

The head has several through holes for attaching it to the cylinder and one threaded one that goes into the combustion chamber for the spark plug. Previously, on many two-stroke engines, another threaded hole was made in the head for the decompressor valve. Now it is played less and less.
In overhead valve four-stroke engines, the head is much more complex: it has sockets, guides and valve channels.
Often, a camshaft with rocker arms is located right there: the head has pipes for mounting the carburetor and the exhaust system.
The shape of the combustion chamber is different. But it is by no means arbitrary, since it strongly affects the quality of combustion. Previously, shapes such as the semi-spherical and "jockey visor" were often used.
Now a chamber has become widespread, as if consisting of two spheres - it provides the most efficient combustion of the mixture.
- I have always been surprised that the number and arrangement of cylinders are indicated in the characteristics of the engine - and not a word about pistons. This is discrimination. The piston is the most important part ...
It's true. The cylinder is passive. The piston perceives the pressure of the hot gases of the combustion mixture and transmits it to the crankshaft through the piston pin and connecting rod. Moving back and forth in the cylinder, it accelerates up to 100 times per second to maximum speed and brakes to zero, experiencing huge inertial loads. Indeed, it is one of the most stressed engine parts.
Consider the structure of the piston (Fig. 26).

Two-stroke engine piston: 1 - bottom; 2- grooves for piston rings; 3 - piston skirt; 4 - boss; 5 - cutouts in the skirt; 6 - window of the odd purge channel

It distinguishes between a head with a bottom 1 and a skirt 3. In the skirt (it plays the role of a guide) there are special lugs - bosses with holes in which the piston pin is located.
On the lateral surface of the head, in its upper part, there are grooves 2. Piston rings are installed in them.
The piston is directly exposed to temperature from the hot gases. It cools badly, only with a fresh mixture and through contact with the cylinder mirror.
Since the piston is cast from an aluminum alloy, it expands significantly when heated. To prevent it from jamming, the piston is installed in the cylinder with a gap. Moreover, the piston height clearance is different: the head has the smallest diameter, the lower belt of the skirt is the largest. In addition, the skirt is also oval in cross section: it is elongated in a plane perpendicular to the piston pin. Given such a complex piston shape, we agreed to measure its diameter in one place: under the lower piston ring. By this size, the pistons are matched to the cylinders.
The pistons of four-stroke low-valve engines have a flat bottom. In overhead valves, it is flat, with recesses for valve protection.
The pistons of two-stroke engines, as you remember, not only compress the working mixture in the combustion chamber, but also control the intake, exhaust and purge. In the skirt of such a piston there are special cutouts or windows that correspond in configuration to the windows on the cylinder mirror. And in the grooves for the piston rings, locking pins are installed, which do not allow the rings to rotate on the piston and thus protect their joints from getting into the windows and from breaking.
The piston rings are split, they are made of such grades of cast iron or steel that have spring properties. Due to this, the rings fit well to the cylinder bore, sealing the gap between it and the piston. Rings for their intended purpose are of two types: sealing (or compression) and oil scraper. The two-stroke engine has no oil scraper rings. On a four-stroke piston, such a ring is installed below the sealing rings. When the piston moves, it removes excess oil from the cylinder walls and dumps it into the crankcase.
More than three rings are not placed on the piston: the degree of compaction increases slightly, and friction losses increase markedly.
The joint of the piston ring is called a lock. Locks are straight or oblique (for a four-stroke engine). On the piston of a two-stroke engine, the ring in the lock matches the shape and position of the locking pin.
The piston pin is steel, hollow, heat treated. In the piston bosses, it is most often installed on the so-called floating fit - that is, it can rotate freely. However, shrink fit is also often used, when the pin is fixed in the bosses and can only rotate in the bushing. The axial movement of the pin is limited by circlips installed in the grooves of the bosses.

Before moving on to another part, let's digress a little and talk about how the cylinder diameter and piston stroke are related.
This is not only interesting, but has a direct bearing on further considerations.
If we compare, for example, these ratios of motorcycles of different years, then even a layman will notice that the process of decreasing the stroke of the piston and increasing its diameter is continuously going on. What is causing this?
First of all, of course, the fact that the motorcycle becomes lighter in this case: the smallest cylinder surface is achieved when the ratio of the piston stroke to the diameter is equal to 1. When the piston stroke decreases, the distance that it travels significantly changes, and, accordingly, the average speed, and this not only prolongs the life of the piston, but also increases the crankshaft speed. It is interesting to note: the value of the average piston speed has remained almost unchanged for many years, since a decrease in the stroke is immediately followed by an increase in the rotational speed - due to this, the power increases.

For four-stroke engines, increasing the cylinder bore is also beneficial because it allows the use of larger valves or, even better, an increase in their number. And this already affects the filling and also raises the power. There is even such a term: "piston power". It is expressed by the ratio in which the area of \u200b\u200bthe piston appears, and allows one to judge the degree of engine acceleration. This area can be increased by increasing the number of cylinders and decreasing the ratio of the piston stroke to bore. In modern engines, this ratio is close to unity. And its decrease below 0.8 is completely inappropriate.
The crankshaft and connecting rod form a crank mechanism. Its main purpose is to convert the reciprocating motion of the piston into rotational motion of the crankshaft.

The simplest crankshaft of a single-cylinder engine consists of main and connecting rod journals and cheeks. The connecting rod journal is enclosed by the lower connecting rod head, on the main shaft rotates in bearings installed in the crankcase. The crankshafts of multi-cylinder four-stroke engines are often cast entirely from ductile iron, and then the journals are machined.
As a rule, the shafts are non-separable. Even in the case when the main journals (axle shafts) and the connecting rod journal are connected to the cheeks in a hot state. So, for example, the crankshaft of the "Ural"

The domestic two-cylinder two-stroke engine "IZH-Jupiter" is essentially two single-cylinder engines "united by a common crankcase. Therefore, the crankshaft is two independent shafts connected by a remote flywheel. The main journals included in the flywheel are fixed with dowels, and the split flywheel is pulled together powerful bolt.
A flywheel is a massive disc usually attached to the end of the crankshaft. Possessing significant mass, and, consequently, inertia, the flywheel, when the crankshaft rotates, accumulates significant energy, which is consumed during auxiliary strokes and smooths out the unevenness of the torque.
Typically, the flywheel of a four-stroke engine is located at the rear end of the crankshaft extending from the crankcase and is part of the clutch. There are usually markings on the outer rim of the flywheel to help set the ignition timing and control the speed. If the engine has an electric start, a ring gear is pressed onto the flywheel rim, which engages the starter gear.
A connecting rod pivotally connects the piston to the crankshaft. In cross-section, the connecting rod most often has an I-beam shape. The preferred material is steel. Structurally, the upper head, the body and the lower head are distinguished in the connecting rod. The upper head houses the piston pin bearing. Before, in most cases it was a bronze bushing. Nowadays, more and more often - a needle bearing: it is more durable and reliable at high speeds.
A bearing is also installed in the lower head. Often its inner cage is the crankshaft neck itself, and the outer cage is a special heat-treated ring pressed into the connecting rod head. Sometimes the lower head is split - then inserts are installed in it.
In contrast to a roller bearing, this is called a plain bearing. This is how, for example, the connecting rod of the Dnepr motorcycle is arranged.

Carter

As the frame connects all the units and assemblies of the motorcycle into one whole, so the crankcase connects the power unit together. Through the attachment points on the crankcase, this unit is most often connected to the frame. The crankcase is cast from an aluminum alloy. Its design significantly reflects the nature of the engine's working process.
For example, the crankcase of a four-stroke engine is most often a single casting with a cavity for the crankshaft, cylinder mounting flanges, oil pump, filter, oil reservoir, etc. In its front and rear walls, holes are made for installing bearings and oil seals.
Two-stroke motorcycle crankcases differ in that they are common to the engine, clutch and gearbox (fig. 28). For the convenience of disassembly and assembly, they are usually made detachable, consisting of two, three, or even more parts. Moreover, the planes of the connector can be both vertical (which is inherent in Russian motorcycles) and horizontal (which can often be seen on Japanese motorcycles).

1 - left cover; 2 - oil filler plug; 3 - gasket; 4 - left and right crankcase halves; 5 - transmission cover; 6 - right cover

There is a crankcase in the front of the crankcase of a two-stroke engine. Since it participates in the gas distribution process, it has to be sealed. For this, a rubber seal (oil seal) is installed in the left half of the crankcase, which prevents oil from entering the crank chamber from the cavity of the motor transmission, and in the right half there is an oil seal that does not allow atmospheric air to enter the crank chamber when a vacuum is created in it.
Next to the crank chamber are cavities in which the shafts and gears of the gearbox, the motor transmission and the clutch are located. The halves of the crankcase are connected with screws. Sealing between the halves is ensured by clean surface treatment and application of glue or sealant.
Additional covers that cover the engine and final drives are usually sealed with thin cardboard or paronite gaskets.

Gas distribution mechanism

- In a two-stroke engine, the master is the piston, he controls the whole process. How do the valves in a four-stroke engine open and close?
Well, in a two-stroke engine, too, everything is not as simple as it might seem at first glance.
When we talked about the diagram and valve timing, we called them symmetrical. It sounds and looks nice, but these phases are not ideal at all. The simultaneous intake of the fresh mixture and the exhaust of the exhaust gases impair the economy and reduce the engine power. That is why it is tempting to somehow separate these processes in order to better clean the cylinders from gases and increase their filling with fresh mixture. This would increase the liter capacity, that is, the power per liter of the displacement.
The most cunning blowdown systems, if they gave any result, were very insignificant.
And then a new idea appeared: to put a spool on the inlet - something like a valve, which would increase the duration of the intake phase and exclude the so-called reverse emission of the mixture into the carburetor. This device is also called a petal valve or a plate check valve.

The first valve was simply a resilient steel plate across the fresh mix flow. He, firstly, showed great resistance to this flow, and secondly, it broke down rather quickly, unable to withstand endless bends - pulsations.
However, "dashing trouble is the beginning." Time passed, new materials appeared, technologies were developed. And now the valves at the inlet began to be serially installed on many motorcycle engines, including domestic ones. And this allows you to save up to 15% of fuel while improving the dynamic performance of the motorcycle.
Inspired by the success, the designers turned their eyes to the release - after all, an ugly mixture leakage occurs there too. And then the valves appeared on the outlet; they were called power. But we will talk about them a little later.
For now, let's get back to the four-stroke engine and its gas distribution system.
It is customary to distinguish between two types of mechanisms: overhead valve and lower valve.
In the first case, the valves are located in the cylinder head and are driven from the camshaft located at the bottom using long tappets, rods and rocker arms. The disadvantages of this system began to manifest themselves more and more clearly as the engine speed increased. After all, even the lightest pushers have mass, which means inertia, and at some stage they began to lag behind. More precisely, they stopped accurately tracking the cam profiles of the camshaft. The phases were violated, and this was a verdict for the overhead valve mechanism.
With lower valve timing, the valves are located in the cylinder body, the drive is carried out by rocker arms or pushers. Such a scheme turned out to be much more tenacious, since the mass of parts moving back and forth is small.
But it was also ruined by congenital defects: a very large surface of the combustion chamber provokes detonation, and the speed of motors with this scheme does not exceed 4500 rpm, which is unacceptably low today.
Much more popular on modern motorcycles is a scheme with an overhead valve, but still with a lower camshaft, which received the symbol OHV from the first letters of the English words Over head valve. In this version, the engine can develop up to 7000 rpm.
When the camshaft was transferred to the head and it began to act directly on the valves through the rocker arms (the scheme is called OHC), the engine got the ability to "spin up" up to 9000 rpm. This option was very popular in the 70s.
Finally, for very high-speed engines, they came up with an option with two camshafts in the head - it is called DOHC (D is a double, that is, a double). There are no reciprocating moving pushers or rods at all - and therefore the motors can develop up to 11-12 thousand rpm.
However, the spring, as it turned out, also has a "response time". And at some, even very high camshaft speeds, it does not have time to unclench. For such especially difficult cases, a so-called desmodromic mechanism has been invented, in which the valves both close and open under the action of the cams, there are no springs in it at all (Fig. 30). This scheme was invented by the designers of the Italian company Ducati. And she paid off her racing engine with a volume of 125 cm3 developed 16 thousand rpm and was at the same time very reliable. This design has only one drawback: it is expensive to manufacture and difficult to operate. However, this does not prevent Italians from using it even on road bikes.

The most common valve timing scheme today is DOHC. Most modern four-stroke engines work on it. Moreover, more and more often, instead of two valves per cylinder, 4, 5, and sometimes even 6 valves are used. As a result, the overall flow area for inlet and outlet becomes larger, cleaning and filling of the cylinders is improved. Smaller valves cool better, their weight is less, which means that you can raise the engine speed even a little. Unfortunately, this complication of the design significantly increases the cost of the motorcycle and therefore is not used in cases where cheapness and simplicity are in the first place.

- In automotive engines, the camshaft is driven by a chain or belt. How is this done in motorcycle motors?
The type of camshaft drive depends primarily on where the camshaft is located. If it is located below, in the crankcase, then everything is very simple: a conventional gear transmission is enough. It ensures accurate valve timing and is very reliable.
If the shaft is in the cylinder head, then the gear drive becomes inconvenient, very cumbersome. And it is being replaced by a sleeve-roller chain. Its advantages are obvious: it is lighter, more compact and cheaper. But the disadvantages are just as obvious. The chain wears out and stretches, noticeably breaking the phases; the chain is "noisy" and requires constant supervision and maintenance.
Therefore, as in car engines, a toothed belt is increasingly used on motorcycles instead of a chain. He, of course, also wears out over time. But the price of a belt is not high, and it is not at all difficult to replace it at the appointed time.
Thus, we have considered the main mechanisms of the engine and now we turn to the consideration of its systems. There are five of them: lubrication, cooling, power, exhaust and electrical systems.

Lubrication system

Friction is the worst enemy of any mechanism, including an internal combustion engine. When the rubbing surfaces are thoroughly treated, there is less friction; with rough processing, the friction forces can reach such values \u200b\u200bthat the parts will be heated up to sintering and melting.
The essence and meaning of the lubrication process lies in the fact that oil is supplied between the rubbing surfaces, forms an oil wedge and separates these surfaces. Dry friction is replaced
liquid, which is hundreds of times smaller. In addition, the oil removes heat from the parts and carries away wear products from the contact area.
A closed circulation lubrication system is traditionally used in four-stroke engines. In this case, oil is taken from the crankcase by an oil pump and is supplied under pressure to the crankshaft main bearings, camshaft, pushers, rocker arms and some other parts, from which it is then discharged back into the crankcase.
Under pressure, and partly by oil mist, the bearing of the lower connecting rod head is lubricated.

Ural motorcycle lubrication system:

1 - oil pump; 2 - oil filter; 3 - pressure reducing valve; 4 - channel for supplying oil to the left cylinder; 5 ~ channels for supplying oil to the casings of rods and cylinder heads; 6 - holes in the piston bosses for lubricating fingers

In some cases, the cylinder mirror, piston and piston pin are lubricated by splashing oil - then the system is called combined.
In descriptions of foreign four-stroke motorcycles, the term "dry sump" is often found. This means that with this design, the oil is stored in a separate oil tank, and after it has worked out in the friction units and is discharged into the crankcase, with the help of a pump, it will immediately go back through the filter to its container.
Initially, two-stroke engines did not have a separate lubrication system - this was their big plus, which reduced the cost of the motorcycle as a whole. Oil in a certain proportion was mixed with gasoline and in this form was supplied to the engine, lubricating all rubbing vapors along the way.
The ratio of gasoline to oil in the mixture depended on the design of the engine and its condition. For domestic engines, as a rule, 400 ml of oil had to be added to 10 liters of fuel, that is, the ratio was 25: 1. In foreign two-stroke engines, where oil was often supplied to the crankshaft bearings separately, the ratio was 33: 1, and sometimes 50: 1.
For all its simplicity and attractiveness, this lubrication method was fraught with many disadvantages.
First, oil and gasoline have different densities and even more different volatility. That is why, getting into the crank chamber, oil immediately settles on its walls, flows down, and a significant part of it does not participate in the lubrication process.
Secondly, with this method of lubrication, it is important that gasoline and oil are thoroughly mixed - and this is not always possible to do. And the consequences of poor mixing can be the most severe for the engine.
Thirdly, the oil in the mixture is supplied to the rubbing vapors always in the same proportion, regardless of the engine operating mode. This leads to a deliberate overconsumption of oil and, which is much worse, to a large release of harmful substances with combustion products.
In addition, oil that enters the combustion chamber along with gasoline settles on the hottest parts of the engine and forms a thick layer of carbon deposits, consisting of heavy unburned tar. This layer impairs the cooling of parts, primarily the cylinder head and piston crown, and can lead to glow ignition and even piston burnout. (Glow ignition is an unfavorable process in which the ignition of the mixture occurs not from a spark, but from hot particles of carbon or metal).
Carbon deposits are actively formed on the electrodes of the spark plugs, increasing the electrical resistance and worsening sparking up to the complete failure of the spark plug.
Agree, there were so many shortcomings that they overshadowed all the advantages of the "good old system". And the designers are actively looking for ways to improve the lubrication system, its optimization. This search led to the creation of the so-called separate lubrication system.
For the first time in domestic practice, it was serially used on a motorcycle IZH-"Planet-Sport" in 1974. And the author had a chance to participate in her tests.
Then, when PS was taken out of production, there was a rather long period of oblivion. And only since 1994, separate lubrication, having survived modernization, having got rid of childhood illnesses, returned to serial IZH and other motorcycles.
The system provides strictly metered lubrication of the parts of the cylinder-piston group and the crank mechanism. It consists of a separate oil tank located in the left crankcase cover, but isolated from the clutch cavity; a screw oil pump located in the same place, oil lines, a spray gun and a control cable connected to the "gas" handle. The main part of the system is the pump. It consists of a screw pump itself, a piston valve sensor, a metering unit and a diaphragm check valve.
Oil through the channel enters the pump casing, is captured by its screw and is fed under the pump cover and further to the sensor valve. Under oil pressure, the piston, overcoming the force of the spring, moves away from the seat (in this case, it opens the electrical contact and the lamp on the instrument panel goes out, indicating that there is pressure in the lubrication system) and frees the oil passage to the dispenser.
We will not dwell on the design of the dispenser. Let's just say that this device is connected with a cable to the "throttle" handle and, depending on the position of the handle (and hence on the engine operating mode), reduces or increases the oil supply.
The diaphragm valve mentioned by us does not allow the oil from the line to drain back into the oil tank when the engine is not running; it serves to regulate the minimum oil supply at idle.
Again, omitting long and detailed descriptions of the processes that are hardly appropriate in our book, “let's say that when using a separate lubrication system, an oil / gasoline ratio is provided from 1: 100 at idle to 1:25 at nominal capacity. operating ratios are from 1:33 to 1:67, and this is not the limit: the designers claim that by using special oils for two-stroke engines and some modification of the pump, oil consumption can be halved again!
It is clear that one application of separate lubrication does not solve all the problems of a two-stroke engine. But it is also clear that this is a very strong move. Therefore, in the 90s, for foreign motorcycles with two-stroke engines, separate lubrication became almost an obligatory design element.

A lot of articles have been written about car engines, there is a lot of different information. There are no so many articles, diagrams, descriptions about motorcycle engines. Let's try to fill this gap. There are a lot of motorcycle enthusiasts. Among them there are also beginners who still know little about the device of internal combustion engines in motorcycles.

On motor vehicles, two-stroke, four-stroke, rotary and boxer engines are mainly installed. The latter are not so widespread, but certain manufacturers use them.

General device and principle of operation

Motorcycles are equipped with units, in the combustion chambers of which the thermal energy released from the combustion of fuel is converted into mechanical energy. The piston of the motorcycle engine perceives the energy of the combustion products, after which the reciprocating movements begin. Thanks to the crank mechanism, the crankshaft rotates. These are the main components in the internal combustion engine.

The crank mechanism practically does not differ from the automobile engine. The piston group is also not much different. The piston here has several rings, a connecting rod and a pin. The total volume of the engine cylinders consists of the working one, as well as the volume (this will be conditionally V) of the cylinders. The ratio of the total displacement of the motorcycle engine to the V cylinders is called the compression ratio. The higher this compression ratio, the more efficiently the motor will work. In modern engines, the compression ratio can reach 9-10 units. And sports engines can have better characteristics - from 12 and higher. I must say that the design of two-stroke and four-stroke engines is slightly different. Let us consider the differences between them now.

Four-stroke engine

In motors of this design, the cycle is four working strokes. What is the essence of his work? In one cycle, the crankshaft makes two revolutions. In the intake phase, the crankshaft goes to bottom dead center, and the fuel mixture enters the cylinder under the influence of vacuum. Next comes the compression cycle. What happens at this moment? The piston rises and compresses the working mixture. At this time, the intake and exhaust valves are closed and the fuel is ignited from the spark plug. When fuel is burned, gases expand significantly and perform useful work. Further, the piston, when moving upward, squeezes out the gases through the exhaust valve.

V-shaped two-cylinder unit

This unit is one of the most ancient. But today this scheme is still alive and in use. This twin-cylinder design with a common crankpin and V-design has no problem with the swinging pair effect. The best camber is 90 degrees. Vibrations from this unit during operation are negligible.

This is an almost ideal motorcycle engine, but the camber angle makes the dimensions larger, which makes it difficult to install it in the frame. But it is possible to do this - this is confirmed by motorcycles from "Ducati". This layout is unconventional, but it still exists on sports cars participating in world championships.

Two-stroke motor

In motorcycle engines of this design, the duty cycle is carried out in one crankshaft revolution. Another feature is the absence of an intake and exhaust valve in the design. Their function is assigned to the pistons. The latter, when driving, open and close the channels for supplying the fuel mixture and exhausting exhaust gases. On some models, a petal valve may be installed at the inlet. There is a crankcase under the piston in two-stroke engines, which also participates in the gas exchange process.

When the piston moves to top dead center, the fuel mixture enters the combustion chamber in the piston space. Gases that remain from the previous cycle are emitted through the piston space. When the windows are closed, a compression cycle begins. A spark ignites the mixture at the top dead center. Then, during combustion, gases are formed, they expand and push the pistons down. When the latter descend by two-thirds of the working stroke, a window will open into the exhaust system. A new portion of the working mixture will flow through the other windows. And when lowering, the piston will create the necessary pressure. This process is called purging, and the channels are called purging. Modern motors have a large number of channels. This is the so-called loopback blowing.

Two-stroke in-line two-cylinder internal combustion engines

Almost all motors operating on this principle work according to the same scheme. It uses the crankshaft, and the connecting rod journals on it are located at angles of 180 degrees. These models have fewer drawbacks compared to their four-stroke counterparts. This can be attributed to the fact that the spark in each cylinder jumps after a full revolution of the crankshaft. As a result, there is no unevenness of flashes, which is found in four-stroke engines.

But the effect of the so-called swinging pair is great. At high crankshaft speeds, this effect can manifest itself in obsessive vibrations. The problem is compounded by the fact that these two-cylinder motors require separate chambers. This means the presence of a central main bearing in the structure, as well as oil seals. As a result, the crankshaft will be wider than in the four-stroke analogue.

Two-stroke V-motor

An engine built according to this scheme is now very rare. One example of such a unit is the NS 250 from Honda.

It was created primarily for the Japanese market. Since the motor is two-stroke, a separate crank chamber is needed, which is constructively impossible. The "swinging pair" cannot be avoided, but the forces that are characteristic of two-stroke engines do not work here.

Inline three-cylinder motor

This transversely mounted unit is a development of the in-line two-cylinder engine. Engineers tried to find compromises between vibration and the size of the four-cylinder internal combustion engine. This scheme was the main one in the 70s.

There are many examples of this. Basically, the Japanese Suzuki and Kawasaki vehicles were equipped with inline three-cylinder engines. There are other motor design schemes. These are four-cylinder, six-cylinder in-line and V-shaped units.

"Dnieper"

This motorcycle was considered a cult among the passionate people. A boxer engine was installed here. Many people criticize this design for its high fuel consumption. But in comparison with other engines of this type, the engine of the Dnepr motorcycle was more perfect.

Device

The placement of the cylinders is opposed here (the same as on other Soviet motorcycles in the heavy class). In terms of design features and technical characteristics, this is a domestic forced internal combustion engine for road-type motorcycles.

Horizontal cylinders cool significantly better, and the crank mechanism is better balanced. As for the power supply system, engineers have provided a separate carburetor for each cylinder. This made starting easier and increased the power of the motorcycle engine.

Unit index - MT8. In addition to design differences, it was superior to other motors in technical characteristics. So, the power is 32-35 horsepower. The maximum speed was 90-105 kilometers per hour if the motorcycle was equipped with a sidecar. Fuel consumption was six liters per 100 kilometers. At the same time, the engine volume of the motorcycle is only 650 cubic centimeters.

Design advantages

The main difference between this engine and all others is the combustion chambers of a more advanced design. They have a cast iron sleeve, which is enclosed in an aluminum alloy cooling jacket. There are no longer cast iron cylinders, which were constantly exposed to overheating in the Urals and other heavy motorcycles.

This approach made it possible to significantly improve cooling and completely eliminate the operation of the internal combustion engine in overheating mode. The Urals came to such a design only in the early 80s. Another feature is a monolithic rather than a composite crankshaft, as well as bushings in the lower heads on the connecting rods (not rolling bearings). This has significantly reduced noise. And the owners also have the opportunity to easily repair the motorcycle engine (in particular, the crankshaft). Moreover, such repairs can be performed up to four times. It was believed that this unit often wedged because of these very liners. In fact, the motor wedged not because of this, but because of the negligent treatment of the owners. The oil was changed out of time, low-quality oils were used in the motorcycle engine. The only drawback of this power unit is the imperfect process of oil filtration using a centrifuge. The rest of the technology was good and very modern.

IZH engines

The IZH motorcycle created in 1987 at the Izhevsk plant is still popular among motorcycle enthusiasts. And there is something to love him for - this is a reliable and high-quality motorcycle. It has a strict classical design and a number of advantages over “Jupiter”. However, there is also a minus - the crankshaft of the IZH motorcycle engine is much larger and more massive. What does this affect? In view of this, the motor runs at lower rpm, thereby reducing power. It is a two-stroke, single-cylinder engine. Fill it with a mixture of oil and gasoline.

With 22 horsepower, the motorcycle's engine displacement is 346 cubic centimeters. This is a good indicator for such a small volume. If you use the unit to the maximum, you can reach a speed of 120 kilometers per hour.

Chinese engines

Now not everyone can afford to restore domestic motor vehicles, purchase high-quality Japanese or American motorcycles. Chinese products are much cheaper and are in good demand. There are no motors designed by Chinese engineers. All units are recycled internal combustion engines from Honda, Yamaha, Suzuki, or licensed units sold from the same brands. The four-stroke examples are quite high quality, as they are made on Japanese lines. But about two-stroke internal combustion engines, many opinions are purely negative.

Motors from China have two markings. One is used for internal use, and the second is needed for the rest of the world. The first letters in the name are the factory. Number 1 means that the motor has one cylinder, 2 - respectively, with two. The third letter is volume. So, I is a 125 cm 3 motorcycle engine. A, B - 50 cm 3, G - up to 100 cm 3. L - up to 200 cubic centimeters.

The owners of Chinese licensed motors claim that in terms of quality and technical characteristics, as well as reliability, they are much better than domestic power units. They are also practically problem-free - you need to understand that this is still not Chinese folk art, but a motor manufactured under license. Even a 250-cube Chinese motorcycle engine will have a sufficient level of reliability.

Motorcycle engine oil

No matter how reliable and stable the power unit is, the quality of its operation depends on what kind of oil the owner uses. Only the product recommended by the manufacturer should be filled. It can be semi-synthetic, synthetic, or even mineral. The oil for each engine is different, and the specific marking must be found in the operating instructions. It is also worth remembering that different lubricants are used for two- and four-stroke engines.

Finally

As you can see, the engine for a motorcycle is practically no different from a car engine. There is a slight difference in design between the two. The principle of operation of power units is the same. These internal combustion engines also have injection power systems, liquid cooling systems are used, and even environmental standards are present. There are models with carburetors - this is also a fairly modern technique. Engines and their designs are constantly evolving, perhaps engineers will soon come up with the perfect motorcycle engine.

The history of motorcycles dates back to the late 19th century. The first representative of two-wheeled vehicles with a motor was the Daimler Reitwagen, created by the legendary German engineers Gottlieb Daimler and Wilhelm Maybach in 1885. It was not like the bicycles of those times (then "penny-farthing" with a huge front wheel and direct drive were in vogue), or modern bikes. However, it was this 260 cc transport, with a capacity of only about 0.5 hp, that gave rise to the birth of the motorcycle industry.

During the 20th century, motorcycles were improved, due to their division by purpose, there was a division into classes. Today, a motorcycle as a whole is a two-wheeled (less often three-wheeled) vehicle with a tubular rudder, a motor located in the frame, and the driver's seat on top (the saddle is between the legs). But this is where the common features of bikes, perhaps, end, since this type of vehicle is very motley. What types of motorcycles are there, how they differ from each other and what they are used for, our material will tell

Classic (road)

Classic motorcycles are vehicles for everyday city driving and covering short distances on the highway. They are the most common and in some countries (such as India) they are still as popular as cars. The classic road bike is the Soviet IZH "Jupiter", and the small-cubic modern "Minsk" (assembled using Chinese components), and the fast-paced Honda CB500F.

The common features of classic motorcycles are: an upright fit with a saddle height of about 80 cm, a moderately curved handlebar, and a small amount of external body kits. They are equipped with a full range of lighting equipment for movement on public roads. The motor and transmission of these bikes have a long service life, as they are designed for everyday riding. Wheels can be cast and spoke, and are usually roughly the same size. The rubber has a combined tread for traction on all types of roads.

The power plants of classic motorcycles are very diverse. Both 2-stroke and 4-stroke motors are used, air and water cooled. They can be in-line, V-shaped or opposed, have from 1 to 4 cylinders. The working volume of a modern road motorcycle ranges from 50 cm³ (if less, this is already a moped) to 1.5-2 liters, or even more. Engine speed is often comparable to that of a car (cruising around 3000 rpm). The road bike weighs around 80-200 kg.

Because modern road bikes borrow features from other classes, they may contain elements typically found in touring, choppers, cruiser and other bike varieties. Because of this, it is not always possible at first glance to identify the "classic", confusing it with a cruiser or a sports bike.

Tourist (tourer)

Touring motorcycles are bikes designed to ride long distances in comfortable conditions. They allow you to cover more than 1000 km per day without getting tired. Usually these bikes are equipped with comfortable soft seats, the passenger saddle may have armrests and a high back. Also characteristic of them are side trunks and a box for storing luggage in the back.

The power plants of turers are usually low-powered, designed for high mileage, relatively slow-speed (2-3 thousand rpm). Their working volume varies from a liter to two or three, while the power is in the region of 50-150 hp. To protect the driver and passenger, the tourers are equipped with wide fenders that protect against splashes and dirt, a windshield or a nose cone. In order to ensure stability, the center of gravity of such bikes is tried to be kept as low as possible. Tourer wheels are usually cast (but there are also spokes), the same or similar in size, with rubber designed for asphalt.

Classic touring bikes include the Honda GL1800 Gold Wing and Harley-Davidson Road Glide. The latter is equipped with a 1750 cc engine with almost 100 hp, comfortable driver and passenger seats (with a supporting backrest), three luggage trunks. For entertainment on the road, a multimedia system is provided on board.

Touring bikes are great for long-distance riding, but they also have drawbacks. The mass of such vehicles can reach 400 kilos (if you drop it, you won't lift it), which affects handling and makes it difficult to maneuver in the city. The price is also a disadvantage of this type of bikes: for the same money you can take a new middle class car. Therefore, tourer is a technique especially for those who are firmly convinced that “4 wheels carry the body, and 2 - the soul”, and who loves a bike more than a comfortable interior of a foreign car.

Sports (racing)

Have you heard or seen something rushing along the highway, making a loud buzz? This is what sports bikes are all about, where the emphasis is on speed and handling. To achieve the best dynamics, engineers equip them with powerful motors, trying to use more light alloys. To improve aerodynamics, sports motorcycles are covered with a body kit made of plastic or thin sheet light metals.

Landing on a sports bike has a forward inclination; for better streamlining, the driver lies on the tank with his chest during the race. Wheels are usually light alloy, with relatively wide rubber (for better grip), smooth tread of the "semi-slick" or "slick" types. Models designed for operation in the city have lighting and a signal, purely sporty (only for the track) bikes are devoid of these elements, which is made to facilitate.

Sports motorcycle motors are high-powered, usually in-line or V-shaped, with 1-4 cylinders. They give out from a unit of volume 2 or more times higher power than classics or tourers. Engines are usually high-speed (up to 10 thousand rpm and more), which is the reason for the characteristic buzzing sound during operation.

Since the races are held in different classes, the engine volume can vary from 100-200 cm³ to a liter or more. In order to ensure handling and safety, sports motorcycles are equipped with powerful brakes. Typical representatives of the sports bike class are the famous Suzuki Hayabusa, the equally famous Yamaha R1, and the Honda CBR1000RR Fireblade.

Alas, such bikes are not well suited for long-term riding, and on roads of average or low quality they do not behave in the best way, and the engine resource is not very large due to forcing. Another disadvantage is the high price (up to tens of thousands of dollars), especially for the fastest models.

Cross (enduro)

Enduro motorcycles are designed for off-road driving, their name comes from the English. Endurance - endurance. The most famous representatives of this class are cross-country motorcycles designed for cross-country racing. An example of a motocross bike is the Kawasaki KXF.

Distinctive features of enduro are "thin" design without heavy parts, the presence of shields that protect the rider from flying dirt and splashes, a body kit made of impact-resistant plastic. The suspension of a cross-country motorcycle is quite stiff, has a hard ride and high reliability, because during the ride you have to overcome holes and jump from hills, and it must keep these shocks.

Since the bike is supposed to be lightweight, manufacturers do not equip it with such excesses as an electric starter, a soft seat, a trunk. The enduro seat is usually narrow and rather stiff, since during the ride a significant part of the load falls on the legs (standing on the footpegs), the rider often has to rise above the saddle.

Models intended only for motocross and not designed for everyday driving on public roads are often deprived of a signal, lighting equipment, since they are not needed at competitions. Enduro wheels are usually spoked, as the spokes are better at distributing shock than cast wheels and are not prone to cracking. Models suitable for city driving usually have a combined tread (for dirt and asphalt), while purely motocross models are equipped with aggressive mud tires with a large pattern.

Most enduros are equipped with single-cylinder motors (both 2-stroke and 4-stroke) that run at high revs to achieve maximum torque. Engine displacement rarely exceeds 500 cm³, although there are exceptions. So, models for long journeys (like the Honda VFR1200X Crosstourer) can have a displacement of more than a liter.

Cruiser

Cruisers are motorcycles with which the image of a biker is commonly associated in the popular mind. Harley-Davidson made a great contribution to the development of the class of such bikes. The model H-D of the Softail series can be considered the standard of the modern cruiser, the classic representative of which is the Harley-Davidson Fat Boy.

Cruiser bikes are characterized by a low seating position (about 70 cm), a soft saddle, a large U-shaped handlebar, and wide footpegs. Thanks to this arrangement, the biker can ride with his body slightly tilted back and his legs put forward. Also, the signature features of cruisers are 2-cylinder V-shaped engines (exceptions are rare), a large number of chrome parts, a teardrop-shaped tank, massive fenders above the wheels.

Very often, cruisers are equipped with tires of different sizes. A narrow rim with a relatively small tire is usually used at the front, while the rear wheel is equipped with a wide tire. The tread pattern is adapted mainly for driving on asphalt. Wheels can be either cast or spoked.

Motors of cruiser bikes have a large displacement, usually from 1 to 2 liters, but are low power and relatively slow speed. Peak torque is typically at around 3000 rpm and peak power at 4000-5000 rpm. Due to this, such bikes are distinguished by high reliability, decent motor life, and also emit a pleasant rumbling sound during engine operation, appreciated by their fans.

Chopper

Choppers are cousins \u200b\u200bof cruisers and share some common traits with them. These bikes are also designed so that the rider can enjoy the ride at a moderate pace. Choppers are often (but not always) equipped with V-shaped motors like cruisers. They have a lot of chrome in the finish, their design has changed little for decades. Usually these are custom motorcycles (there are few serial ones), but since they are clearly distinguishable from the background of other class, it is worth taking out choppers in a separate item.

The characteristic features of the choppers are an elongated frame, a relatively small teardrop-shaped tank, a simplified instrument panel and minimalistic lighting technology, small or completely missing fenders. The front disc of these bikes is usually larger than the rear, but with narrower tires. A small disc is used at the back, but it has a massive wide tire on it.

The most important feature of the chopper, which allows it to be identified with 100% accuracy, is the front fork. It is complemented by a steering wheel with a clearly defined U-profile that projects forward. For some choppers the length of the fork reaches about 2 meters, so it is located at a large slope.

Serial motorcycles of this type are almost never produced, usually these are the fruits of the creation of a gloomy genius. In the West, Harley-Davidson, Indian bikes often become the basis for building choppers. In Russia, fans of choppers with a limited budget build them on the basis of heavy motorcycles "Ural" and "Dnepr". The motor is left either native, 650-750 cc boxer, or a subcompact car engine is installed. 1200cc V4 engines from Zaporozhets are especially popular among enthusiasts.

Dragster

Dragster - A type of motorcycle (small-scale or custom) for speed competition at a short distance (usually a quarter mile), called drag. Since the goal of the race is to complete the track in the shortest possible time, these bikes are equipped with very powerful motors. In some cases, they can develop about 1000 HP and even more.

Dragsters are heavy, therefore they are equipped with supporting side wheels that do not allow to fall at the start or when tilting. Since the competition takes place on a straight road, their controls are extremely simple. Usually the steering wheel of such a bike is straight and narrow so that during the ride the rider's hands do not create unnecessary air resistance.

Landing is usually low, for the best streamlining the rider rests on the tank with his chest. The front fairing also improves aerodynamics. For these reasons, the handling of the dragsters is extremely low, which makes them unsuitable for driving on public roads.

For the best grip and a sharp start without slipping, the rear wheel of the bike is made as wide as possible. For road racing, a smooth tread without pronounced spikes is used, and for competition on the ground, mud tires can be installed. The suspension of the dragster is extremely simple, often they are hardtails and lack shock absorbers.

Custom

Custom - a wide class of motorcycles made individually in single copies. Bikes of this type are very motley, since everything is limited only by the imagination of their creators. Custom can be road, sports, cross-country bikes, choppers, dragters, tourers, as well as their subtypes.

Harley-Davidson CVO Street Glide © Holstein "s Harley-Davidson

Usually, custom cars differ from production models by the presence of deep tuning. It is produced with the use of forced motors of increased power, reinforced frame elements, modified or custom-made structural parts. An example of a factory custom is the Harley-Davidson CVO series.

In exceptional cases, a custom bike can have the most bizarre shapes. For example, dragters equipped with jet-powered engines are being created to set speed records. Craftsmen also assemble choppers equipped with radial-type aviation power plants (“star”) or multi-cylinder motors from sports cars.

Electric bike (electric bike)

An electric bike is a relatively new type of motorcycle that uses an electric motor instead of an internal combustion engine, powered by batteries. It can have a capacity from hundreds of watts to tens of kilowatts. To extend the power reserve, such bikes are lightened as much as possible, their parts are made of light alloys and polymer composites, such as carbon fiber. For the same purpose, these motorcycles have an aerodynamic body kit designed to reduce air resistance.

The appearance of an electric bike can match almost any type of ICE motorcycle, but more often than not they are very similar to road, sports and motocross models. For example, the Alta Redshift SM looks very much like an enduro (but without the "evil" rubber), and the Lightning LS-218 is a typical sport bike.

Conclusion

The division of motorcycles into types allows you to group them according to design criteria and scope of use, but sometimes it is conditional. Very often bikes combine features of several classes, for example, a road bike may look like a sports bike, and a cruiser may look like a classic model. Therefore, it is not always possible to identify the exact belonging to a certain class at first glance.

Also, within each type, there are subtypes with a narrow specialization. Some of them are mentioned in our material (for example, enduro especially for cross). But if we consider each of the subtypes in detail, this is already information that requires not an article on the site, but an entire encyclopedia. Therefore, we limited ourselves to only the main varieties of motorcycles.

Description of the main components of the motorcycle, the rules for their operation and recommendations for simple repair and maintenance. This material will be useful for novice motorists.

Motorcycle engine.
Motorcycle engines are 2-stroke and 4-stroke. A positive feature of 2-stroke engines is the large liter capacity. The negative side is the increased requirement for lubrication, and as a result, a low resource. The separate lubrication system consists of an oil tank and a pump combined with a metering mechanism. This device supplies oil in a ratio of 1 to 60, 1 to 100, so if you do not use a special 2-stroke oil, the engine will fail. The design of 4-stroke motorcycle engines is similar to automobile engines, but, as a rule, the engine is combined with a gearbox and has a single lubrication system.
It is recommended to change the oil and oil filter after 5-10 thousand kilometers or once a season. Use a special 4-stroke oil, as motorcycle clutches work in an oil bath and some automotive oils contain additives that form surface films, which can lead to premature disc wear.
The gas distribution mechanism requires periodic adjustment. The most common method is a rocker or rocker screw with a locknut. There is an adjustment with washers that are placed under the pusher glass, as on a VAZ 2108 car. Engines with hydraulic compensators do not require maintenance of this mechanism.
The valve clearances are usually set: for liquid-cooled engines, 0.08-0.1 mm at the inlet and 0.1-0.15 at the outlet. For air-cooled engines, they are slightly higher: 0.1-0.15 at the inlet, 0.15-0.25 at the outlet. This is averaged data. Often, poor compression is associated with missing or incorrect valve clearance.

Motorcycle cooling system.
In the water cooling system of 2-stroke and 4-stroke engines, a forced cooling fan is usually provided. It turns on when the temperature rises above 85 - 90 degrees. If the temperature rises above 100-105 degrees (red zone on the sensor), and the fan does not turn on, check the fuse. If it is intact, you need to check the fan switch, which is usually located at the bottom of the radiator. To check the inclusion, it is enough to connect the terminals removed from the sensor together, and if one wire is suitable, connect it to ground. In this case, the fan should start working. If it turns on, and when the motorcycle overheats, it does not rotate, then the sensor must be replaced. The fan may also not turn on due to poor coolant circulation or low coolant level.

For air cooling systems, the condition of the air filter is an indispensable condition for the normal operation of the engine and its longevity. A dirty filter does not allow the engine to develop the required speed, power decreases, and fuel consumption increases. This filter should be changed. A filter made of foam rubber should be washed periodically. After drying, the filter must be soaked in special filter oil. If this is not done, it will lose its filtering properties.

One of the causes of engine malfunction is a fall. When, during a fall, the engine continues to operate in a mode close to the maximum, the exposed oil receiver does not allow oil to flow to the crankshaft liners and the distribution mechanism, which leads to their emergency wear.

Spark plug.
The most capricious part in a motorcycle engine is the candles. It is worth starting the engine several times in a row and not warming it up, as they immediately become covered with condensation, and further starting is difficult. Usually, it is enough to warm up the engine to operating temperature and the problem disappears - the plugs reach the self-cleaning temperature. Use only the original spark plugs specified in the catalog for installation on your motorcycle.
When starting after a long stay, for example, in winter, there may be a shortage of gasoline in the fuel mixture, despite the included enricher. You can correct the situation by blocking the air filter inlet with your hand or a rag. When starting a cold engine, it is also not recommended to turn the "throttle" handle with an extended "suction".

Motorcycle carburetor.
"Either nothing or nothing" - that's what the mechanics say when the motorcycle engine won't start. If there is a spark and sufficient compression (9-12 kg / cm2), check the carburetor. Water that has accidentally entered the carburetor can be removed without removing it from the motorcycle. For this, most models have a special screw in the bottom cover. It is enough to loosen the tapered needle of the valve with a screwdriver or hexagon and drain the sediment. The same screw can be used to test the check valve.
Freed from the cables and extracted from the bowels of the motorcycle, the carburetor conceals several pitfalls:

• rail of 2-4 carburetors, it is not recommended to disassemble. As a rule, all the main systems are available anyway, but if the rotary damper is backlash, you cannot do without disassembling the entire rack. It is important to remember the location of the springs that press one rod against the other. Do not touch the adjusting spring-loaded screws when disassembling;
• under the cover of the float chamber are: floats, a needle valve and nozzles. Usually, after long periods of inactivity, a large layer of plaque forms in the carburetor, which can fill the entire float chamber. It has to be removed mechanically. This must be done carefully and carefully. Never use steel wire to clean the jets, but rather take a strand of copper wire. Plaque and debris must be removed not only from the jets, but also from the channels of the carburetor body. On some models, the starting enrichment jet is built into the float chamber cover and is often overlooked. If the seat of the needle valve is removable, check that the mesh underneath is clean;
• the throttle valve in modern constant vacuum carburetors is lifted by a rubber diaphragm. You need to be extremely careful with her. If the membrane is torn, then it is impossible to glue it, buying a new one will not be cheap. A soft spring presses the throttle, which should be similar in elasticity to the springs of neighboring carburetors. Hence the conclusion - not to change it or stretch it;
• the mixture quality is adjusted at the factory, and during operation it is not necessary to change it, since this requires special devices. If, when cleaning the carburetors, it is necessary to unscrew the adjusting screws, first check how many revolutions they have been unscrewed. After cleaning, put everything back in place.

Motorcycle front fork.
If the motorcycle has a leaking shock absorber front fork, and there are no traces of pitting corrosion or scratches on the working surface, you can just replace the oil seals. When the working surface has pits of corrosion, it is necessary to polish them, and it is better to solder the shells with tin. Only in this case, replacing the oil seals will give the desired result.
Front suspension knocking can be caused by clearance in the steering column bearings or worn out front wheel bearings. It is better to entrust this repair to a specialist.

Rear suspension of a motorcycle.
Knocks in it will appear with increased gaps of a progressive suspension with a monoshock. The knocking can also be caused by wear on the rear wheel bearings. Rear suspension shock absorbers are difficult to repair, so if they are out of order - contact a specialist or purchase new ones. If you have an enduro that is operated off-road, we recommend that you disassemble and lubricate the rear suspension arm system once a year.

Motorcycle chain.
A modern chain has rubber seals in each link and serves for a relatively long time (20-50 t.km.). To increase the service life, it is better to lubricate it periodically (500-2000 km). remember to do this after riding in the rain or on a muddy road. It is best to use a special lubricant in aerosol cans. Servicing the chain is best done after the ride. it takes time for the grease to cure. Pay attention to the correct tension of the chain - the slack of the lower branch should be within the range of three to five centimeters.

Motorcycle electrical equipment.

If you accidentally reversed the polarity of the battery, do not worry too much, the fuse installed for this case usually blows. If the electrical malfunction is more complex than a burned-out light bulb, contact a specialist. The main reason for the failure of the electronic systems of the motorcycle is overvoltage in the on-board network, the cause of which is often simply poor contact of the battery terminals.

A motorcycle powered by an internal combustion engine is a fast two-wheeled vehicle. By design, motorcycles are divided into single (Fig. 1) and with a sidecar (Fig. 2). Depending on the purpose, motorcycles are road, sports and special.

Figure: 1. Road bike "Sunrise"

There are two more mechanical means of transport intermediate between a motorcycle and a bicycle: motorbikes and mopeds.

Figure: 2. Road bike with a sidecar IZH "Jupiter"

Depending on the working volume of the engine cylinders, motorcycles are divided into ultra-light (50-100 cm 3), light (125-250 cm 3), medium (350-500 cm 3) and heavy (over 500 cm 3).

Below are the basic data of road bikes.

The motorcycle has the following mechanisms and systems: an engine with power supply, lubrication, cooling and ignition systems serving it, a power train, a chassis, and control mechanisms.

Engine converts thermal energy into mechanical energy, which, using a number of mechanisms, sets the motorcycle in motion.

Power transmission (Fig. 3) brings the force developed on the engine crankshaft to the drive wheel. This includes forward gear, clutch, gearbox and reverse gear.

There are three types of power transmission: chain, cardan and direct.

The chain drive (Fig. 4, a) transmits the rotational force or torque of the engine by the motor chain to the clutch, and through it to the gearbox, from where the rear chain to the driving wheel of the motorcycle.

With a cardan drive (Fig. 4, b), the torque from the crankshaft is transmitted through the clutch directly to the gearbox, from where, using the cardan shaft and main gear, to the driving wheel of the motorcycle.

Direct transmission consists of a gear transmission (motor), which, through the clutch mechanism and the gearbox, transfers the force to the shaft, which is also the axle of the wheel.

Chassis ensures the movement of the motorcycle and serves as a skeleton for fastening its main mechanisms. It includes the frame, front fork, wheels with tires, saddle, rack, footpegs, stand, mud guards and a towed stroller.

Control mechanisms designed to control a motorcycle while driving, as well as to operate its units and devices. Control mechanisms include steering, brakes, and controls.