Engine for a walk-behind tractor: Chinese OHV diesel engine, what is a single-cylinder petrol engine for a walk-behind tractor, which is the best four-stroke

In recent years, many useful devices with internal combustion engines (ICE), both domestic and professional, have appeared on the market. These include mini power plants, motor pumps, lawn mowers, motor cultivators, and snow blowers. Motorized concrete mixers, welding motor generators, vibratory rammers, vibrators, etc. are used in construction. Most of them are equipped with single-cylinder, gasoline-free, four-stroke, air-cooled internal combustion engines. Diesel engines are less common, but this topic deserves separate consideration.

The engine is the most complex and expensive component of most of these devices. Therefore, we will consider the characteristics that should be taken into account when choosing an engine.

According to the power supply system, almost all gasoline engines used are carburetor engines. Most of them use an electronic ignition system, although the cheapest examples have a magneto ignition system. Electronic ignition is preferable because it ensures good engine starting in various conditions.

Single-cylinder engines mainly use air cooling. For intensive heat removal, the piston group uses cylinders made of aluminum alloys with cast iron inserts or completely cast iron cylinders. Cast iron cylinders are more preferable because The service life of the engine is significantly increased. Although the use of aluminum cylinders with cast iron inserts is quite acceptable when operating the engine in “home” conditions, for example, in a power plant, which is used as a backup during rare outages of the main power supply. Or in a lawn mower, which is used in the summer once a week for an hour or two. For professional use, say in construction equipment during daily long-term work, an engine with cast iron cylinders is a prerequisite for its reliable operation.

The presence of an oil level sensor is essential. The simplest way to ruin an internal combustion engine is to operate it with a low oil level or no oil at all. If there is a sensor, an engine with insufficient oil in the crankcase simply will not start. Although all operating manuals call for checking the oil level in the engine before starting it, as repair practice shows, not everyone follows this simple and very reasonable recommendation.

The most significant impact on the price and characteristics of the engine is exerted by the gas distribution mechanism used in it. Currently, the single-cylinder engines under consideration use three types of valve timing mechanisms: SV, OHV and OHC. All three types have been used previously or are currently used in automobile engines.

Engines type SV

- English abbreviation side valve - engines with side valves. In the domestic literature, such engines are often called lower valve engines. In fact, the intake and exhaust valves are located at the bottom and side of the cylinder. The camshaft is also located at the bottom and is most often gear driven from the crankshaft. Single-cylinder engines with this arrangement are produced in large quantities by all major global manufacturers Honda (G series), Subaru-Robin (EY series), Briggs & Stratton, Tecumseh and others. Such engines usually run on low-octane gasoline (no higher than 92) and do not like high speeds. These engines are inexpensive and reliable, although they have slightly higher fuel consumption compared to OHV and OHC. They work very well in mini-power plants where the engine speed is kept fixed (usually 3000 rpm). In most cases, these engines are recommended for home use, although Japanese engines of this type (Honda, Robin) have a very long service life and work well in professional equipment.

Interestingly, in the automotive industry, engines of this type were popular in the 30s of the 20th century. They lived longer in Soviet cars and were installed on Pobeda, ZIS, Moskvich 401 and some trucks (mainly GAZ). The main inherent disadvantages of this design are associated with the large surface of the complex shape of the combustion chamber and the ineffective way of operating the combustible mixture, which increases fuel consumption and heat losses in the engine. Because of this, engines are prone to detonation of the fuel mixture and cannot operate on high-octane gasoline. On the other hand, a simple gas distribution system and good lubrication conditions for all its parts are the key to reliability.

Device

The classic walk-behind tractor engine is a single-cylinder, four-stroke internal combustion engine.

The crankshaft of this engine is mounted in two ball main bearings and, on one side, has a landing cone for the flywheel, also known as an ignition rotor and cooling fan, and on the other, a conical or cylindrical fit for a pulley or clutch.

The connecting rod of a walk-behind tractor is a detachable structure that works directly along the crankshaft journal as a plain bearing.

The friction pair is lubricated by an oil-catching protrusion on the bottom cover of the connecting rod; forced oil supply from the pump is not provided.

The cylinder is installed at a slight angle to the horizontal, its cooling jacket is cast integrally with the crankcase, and a cast-iron sleeve is pressed into it. This solution reduces the cost of engine production, but makes its repair more difficult, since replacing the cylinder is impossible.

The cylinder-piston group is lubricated by oil splashes created by the connecting rod and the crankshaft counterweights as it rotates. First of all, you need to know what kind of oil to pour into the walk-behind tractor, what kind of oil is poured into the gearbox and into the 4-stroke engine.

For more information about the operation of a single-cylinder engine, watch the video:

Depending on the layout of the gas distribution mechanism, the engine can be:

• Overhead valve (SV) - the camshaft is located in the crankcase and, through short pushers, directly drives the valves located on the side of the cylinder. The cylinder head in such engines is a simple casting with a combustion chamber of a specific (cardiod) shape.
• The bottom valve arrangement is the oldest used in our time, it is almost a hundred years old. Due to their extreme simplicity, such motors are cheap and reliable, but their main drawback is their low power density.
• The incorrect term “side-valve engine” is also often used, which appeared as a literal translation of the English side-valve due to ignorance of the term “lower-valve”, which has been adopted in Russian since the 30s of the twentieth century.
• Overhead valve (OHV) engines also have a camshaft mounted in the crankcase, but the valves themselves are already in the cylinder head and are actuated by long rods through rocker arms.
• Due to the more compact and advantageous shape of the combustion chamber, overhead valve engines are noticeably more powerful than lower valve engines, but at the same time they are easy to assemble and configure. This is the most common type of motor in garden equipment.
• Overhead (OHC) engines differ in that the camshaft is moved to the cylinder head. They are more complex compared to OHV engines, and they gain in power only at high speeds, which is of little relevance for walk-behind tractors. Nevertheless, some manufacturers, for example Subaru-Robin, use this scheme.

Engines of relatively large volume (from 200 cm3, as well as diesel) have a manual or automatic decompressor as part of the gas distribution mechanism - a device that at low speeds increases the opening time of the exhaust valve, thereby reducing the effort to manually start the engine.

Story

1904 patent for Buick's overhead valve engine.

Predecessors

The first internal combustion engines were based on steam engines and therefore used slide valves. This was the case with the first Otto engine, which was first successfully launched in 1876. As internal combustion engines began to develop separately from steam engines, poppet valves became increasingly common, and most engines until the 1950s used a side valve (flat head) design.

Beginning with the 1885 Daimler Reitwagen, some cars and motorcycles used intake valves located in the cylinder head, however these valves were vacuum actuated ("atmospheric") rather than camshaft actuated as in typical OHV engines. The exhaust valve(s) were actuated by the camshaft, but were located in the engine block, as in side valve engines.

The 1894 prototype diesel engine used overhead poppet valves actuated by a camshaft, pushrods, and rocker arms, making it one of the first OHV engines. In 1896, William F. Davis was awarded U.S. Patent 563,140 for an overhead valve engine with liquid coolant used to cool the cylinder head. but no working model was built.

Series OHV engines

In 1898, bicycle manufacturer Walter Lorenzo Marr in the United States built a prototype motorized tricycle powered by a single-cylinder overhead valve engine. Marr was hired by Buick (then called Buick Auto-Vim and Power Company

) in 1899–1902, where the overhead valve engine design was further developed. This engine used rocker arms driven by pushrods, which in turn opened the valves parallel to the pistons. Marr returned to Buick in 1904 (building a small number of Marr Auto-Cars with the first known engine to use an overhead camshaft), the same year Buick received a patent for an overhead valve engine design. In 1904, the world's first production OHV engine was released in the Buick Model B. The engine was a flat twin design with two valves per cylinder. This engine proved to be very successful for Buick, with the company selling 750 of these cars in 1905.

Several other manufacturers began producing overhead valve engines, such as the vertical 4-cylinder engine

Wright Brothers 1906–1912. However, side-valve engines remained common until the late 1940s, when they began to be phased out for OHV engines.

Overhead Cam Motors

The first overhead camshaft (OHC) engine appeared in 1902, but for many decades the use of this design was largely limited to high-performance cars. OHC engines gradually became more common from the 1950s to the 1990s, and by the early 21st century, most automobile engines (with the exception of some North American V8 engines) used the OHC design.

At the 1994 Indianapolis 500 auto race, Team Penske entered a car powered by a custom Mercedes-Benz 500I engine. Due to a loophole in the rules, the pushrod engine was allowed to use larger displacement and higher boost pressure, greatly increasing its power output compared to the OHC engines used by other teams. Team Penske qualified on pole position and won the race by a wide margin.

In the early 21st century, several pushrod V8 engines from General Motors and Chrysler used variable displacement to reduce fuel consumption and exhaust emissions. In 2008, the Dodge Viper (fourth generation) introduced the first production pushrod engine to use variable valve timing.

Engines made in China

Chinese motors for walk-behind tractors are most common on budget vehicles and can differ noticeably in quality.

If units from major manufacturers (Lifan, Zongshen) copied from the Honda GX are close to the Japanese original in quality and durability, then cheaper ones, often not even labeled by the manufacturer, still retain the famous lottery “Chinese quality”.

Many manufacturers of cheap walk-behind tractors, when ordering such motors, put their brand markings on them.

Let's look at the most common types of engines (since the same engine can be produced by a dozen companies, it is pointless to distinguish Chinese engines by brand in this regard):

The lowest power (4 hp) engine for light walk-behind tractors and cultivators. The model for its creation was the Honda GX120 engine.

It is also the cheapest Chinese motor - it costs no more than 5-6 thousand rubles.

The most popular engine model copied from the Honda GX160. This is a gasoline engine with a power of 5.5 horsepower and a displacement of 163 cm3.

Thanks to its simple and reliable design, this motor can be found on walk-behind tractors, cultivators, gas generators, motor pumps and many other units with gasoline engines.

Mini-class equipment is widely used in personal plots and even in public utilities. Mini tractor Bulat 120 is an indispensable assistant for farmers and summer residents.

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This engine can only be started with a manual starter. The gas distribution system is OHV; thanks to the successful layout, adjusting the valve clearances is very simple and quick. The engine can be additionally equipped with an oil level sensor and a generator light winding.

Gasoline four-stroke two-cylinder engine 680 cc.

The proposed motor is equipped with all systems and does not require additional equipment with domestic parts and devices that are not reliable. At the same time, it does not use complex electronic systems, which adds to its reliability and ease of operation. All adjustments are already installed at the manufacturer and during modification by our company. We install the leading variator regulator of the “Safari” type on the crankshaft of the engine. At the same time, the engine is modified to work correctly with the variator. We connect the throttle cable to the throttle control rods. Installation on a snowmobile will require a minimum of skills and time from you. The procedure for carrying out the work is described in the installation instructions. The engine will provide your snowmobile with a maximum speed of up to 60 km/h on compacted surfaces. The speed and dynamics of acceleration when driving on virgin soil are not inferior to a snowmobile with its original engine.

Unlike analogues, to increase reliability and protect the engine from damage when the snowmobile rolls over, our 2-cylinder engines are additionally equipped with an oil pressure sensor, which turns off the engine when the pressure in the oil line drops.

Our 640 cc engines are equipped with powerful generators: 20 A, 240 W

, which will allow the owner of a snowmobile with such an engine not to limit himself in the use of lighting and heating devices - heating of the handles, trigger and seat.

Technical characteristics of the four-stroke two-cylinder engine for the Lynx snowmobile:

Displacement 680 cc Power at 4600 rpm. 32 hp Engine weight 43 kg Crankshaft shank diameter 28.5 mm Crankshaft shank length 94 mm Overall dimensions: depth from the end of the crankshaft variator drive pulley adjuster to the rear plane of the engine 520 mm width 480 mm height along the muffler 450 mm height with the muffler and housing removed air filter 400 mm Height of the axis of the crankshaft shank from the plane of the base 132 mm Distances between the motor mounting holes on its base 198x110 mm Volume of oil poured into the crankcase about 1900 ml Cooling - forced air Oil type 5w-30, 10W-30

1. Fuel economy is 1.5-2 times thanks to the 4-stroke cycle. 2. High speed under load. 3. Better acceleration dynamics due to higher torque. 4. Saving oil, which does not need to be mixed with fuel. 5. Cleaner exhaust due to the absence of oil in gasoline and complete combustion of the fuel mixture. 6. Easy starting due to the absence of oil in the fuel and a more advanced carburetor. 7. Greater resource. 8. Greater reliability due to the quality of manufacturing and layout of all systems in one unit on the engine. 9. The engine is equipped with both a manual and electric starter.

The cost of a two-cylinder four-stroke gasoline engine 680 for the Lynx snowmobile is 67,000 rubles.

GreenField

The “GreenField” trademark belongs to the Russian TechnoGroup LLC. Since 2005, under it, a variety of garden equipment, gas-powered tools, and power electrical equipment have been supplied to the Russian market.

When buying a motor for a Greenfield walk-behind tractor, you need to understand that the Russian brand in this case is simply applied to a Chinese product, the selling company only carries out quality control on the products supplied to it from China.

Naturally, Greenfield engines, like other Chinese products, are either completely copied from Honda GX engines (GreenField GF series), or based on their design with minor changes (GreenField PRO). However, PRO engines do not have options with an electric starter or reduction gearbox.

The company also supplies diesel engines with power from 2.8 hp. (GF170F) up to 11 hp (GF188FDE). Prices vary quite a lot between stores, but in general they are comparable to Lifan motors.

Diesel engine for walk-behind tractors

Today, Chinese walk-behind tractors are very popular in the agricultural machinery market. They are the best choice for all farmers who are trying to find a balance between reasonable price and high quality. When choosing a Chinese diesel walk-behind tractor, you must carefully study all the characteristics of its engine. Often, engines for walk-behind tractors are produced by well-known brands.

A diesel engine is an internal combustion engine that operates on the principle of self-ignition of atomized fuel. The diesel engine for the walk-behind tractor is a four-stroke model with a power of 4 to 9 kW. In this case, the tank volume is no more than ten liters. This engine power should be enough for the unhindered movement of the walk-behind tractor, including soil resistance.

There is no fundamental difference between Chinese and European walk-behind tractors, which only simplifies their operation and maintenance. During their production, the same kinetic relationships are used, which significantly increases the level of unification and standardization of the necessary equipment and components.

Advantages and Disadvantages of SOHC

• cheap and easy maintenance due to its simple design;
• the possibility of installing turbochargers with a V-shaped valve arrangement;
• Possibility of self-repair and maintenance of the motor.

• much lower efficiency compared to DOHC;
• high consumption relative to a 16-valve engine due to insufficient power;
• significant reduction in engine life during tuning;
• the need for more frequent attention to the timing system (adjusting valves, inspecting pushers, replacing the timing belt).

Home » Articles » DOHC and SOHC engines: differences, advantages and disadvantages Sources used:

Advantages of a diesel engine

The engine on a diesel walk-behind tractor has a number of distinctive features that you must know before using it.
Most modern engines typically operate on a four-stroke cycle. These motors are very reliable and more efficient in operation. Over the past few years, the diesel engine on a walk-behind tractor has gained great popularity. It is preferred by experienced farmers.

Such motors can develop incredible power at minimal cost. They can serve for a very long time.

When choosing an engine, be sure to remember that the duration of its operation directly depends on the power. The main feature is that the greater the engine power, the easier it can bear loads, and thus will last much longer. Main advantages of a diesel engine:

• fairly low fuel consumption compared to a gasoline engine;
• significantly less harm to the environment;
• better grip due to greater weight;
• The engine is much more durable and reliable than a gasoline engine.

The most popular and in demand are walk-behind tractors with a diesel engine such as “Centaur”, “Bison”, and “Scout”.

How Otto developed the engine

The unit, invented by a scientist named Alphonse Beau de Rocha, and then built by the German engineer Nikolaus Otto in 1867, was considered in those years to be the maximum of manufacturability and almost perfection. There were simply no analogues for it. The motor was very inexpensive to operate, had a compact size, and also did not require frequent maintenance.

The operation of the four-stroke engine was built according to a clear algorithm. Today it is called the "Otto cycle". In 1875, Nikolaus Otto in his company produced more than 600 engines per year.

Read also: Hydraulic diagram of a rolling jack

Review of single-cylinder internal combustion engines

In recent years, many useful devices with internal combustion engines (ICE), both domestic and professional, have appeared on the market. These include mini power plants, motor pumps, lawn mowers, motor cultivators, and snow blowers. Motorized concrete mixers, welding motor generators, vibratory rammers, vibrators, etc. are used in construction. Most of them are equipped with single-cylinder, gasoline-free, four-stroke, air-cooled internal combustion engines. Diesel engines are less common, but this topic deserves separate consideration.

The engine is the most complex and expensive component of most of these devices. Therefore, we will consider the characteristics that should be taken into account when choosing an engine.

According to the power supply system, almost all gasoline engines used are carburetor engines. Most of them use an electronic ignition system, although the cheapest examples have a magneto ignition system. Electronic ignition is preferable because it ensures good engine starting in various conditions.

From a four-stroke internal combustion engine to a car

The team of engineers who worked on the creation of the unit included one talented guy - Gottlieb Daimler.

He was then passionate about the idea of ​​​​creating a real car based on this engine. But Otto did not want to modernize an already successful engine. Daimler was forced to leave the project, but the desire to build a car did not go away.

As a result, together with his friend and like-minded person in 1889, Daimler assembled a car based on a four-stroke gasoline engine operating according to the Otto algorithm.

OHV engines

OHV engines

- English abbreviation overhead-valve - engines with overhead valves. The intake and exhaust valves are located on top of the cylinder. The camshaft is located at the bottom and is most often gear driven from the crankshaft (sometimes chain driven). Valves are opened and closed using pushrods, rods and rocker arms. All major world manufacturers Honda (GC series), Subaru-Robin (EN series), Briggs & Stratton (Vanguard), Tecumseh and others have single-cylinder engines with this arrangement in their program. These engines usually run on 95 octane gasoline. These engines are somewhat more expensive than the SV, are very reliable, durable and economical and are somewhat less noisy. They work stably in a wide speed range and are elastic. These properties are mainly due to the optimal shape of the engine combustion chamber. They do not like very high revolutions (more than 6500) due to the complex and rather long gas distribution system, in which at high revolutions the rigidity of the system and the accuracy of the valve timing decreases. These motors are recommended for use in professional equipment. They are universal and find application in almost all types of devices.

In the automotive industry, engines with this gas distribution pattern are currently most often found on American gasoline engines, installed mainly on jeeps and pickups and on low-speed diesel trucks. It is not uncommon for automobile engines of this type to go through a million kilometers without major overhaul. Of the domestic engines, the most famous (unfortunately not from the best side) are the engines of the Zavolzhsky Motor Plant ZMZ-401, 402, which were installed on Volga and other cars for several decades, as well as the V-shaped ZMZ-53, which was installed on trucks.

How does a single cylinder four stroke engine work?

These motors are quite widespread both in cars and in other vehicles such as motorcycles, tractors, mopeds. In addition, China produces single-cylinder engines with a volume of 1.03 liters, which are used to drive heavy walk-behind tractors. The main advantages include the smallest ratio of cylinder area to working volume, therefore heat loss is minimal, and the indicator efficiency is quite high .

The design of a single-cylinder diesel engine, like a gasoline engine, is as follows. In total, such engines have four strokes, the first stroke is responsible for the intake. Initially, the piston occupies a position at the upper limit or dead point (TDC), and the crankshaft, turning 180 degrees, moves it to the lowest point, also called dead point (BDC). In addition, the intake valve also opens, and thanks to the vacuum formed in the cylinder, a combustible mixture is literally sucked into it, which, mixed with the combustion products remaining in it, forms a working mixture.

During the next stroke - compression, the piston returns back to TDC, during this period both valves are in the closed position, which contributes to the compression of the working mixture, and, consequently, an upward jump in temperature and pressure. Next comes the power stroke (third stroke) from the spark created by the candles, ignition and combustion of the mixture occurs, also leading to a sharp increase in these indicators.

The piston descends and pushes the connecting rod, which, making a rotational movement, acts on the crankshaft. At this moment, the transformation of thermal energy into the mechanical energy we need takes place. The exhaust valve also opens, resulting in a decrease in temperature and pressure. The last stroke is responsible for the release of exhaust gases through the exhaust valve into the muffler and then into the atmosphere.

OHC type motors

OHC engines are by far the most common in the automotive industry. The same cannot be said about the use of this arrangement in small single-cylinder gasoline engines. The abbreviation OHC stands for overhead-camshaft, translated from English as “overhead camshaft”. In such power units, the camshaft cams press on the valves directly through pushers, or less often through rocker arms. The drive from the crankshaft to the camshaft is most often carried out by a chain or timing belt. The advantages of such an engine are precise operation in a very wide speed range, efficiency, reliability, low noise, and long service life. Such engines can quickly gain speed and drop them just as quickly, which allows the engine to quickly adapt to frequently changing loads and not reduce the specified power. OHC engines make maximum use of the positive qualities of the electronic ignition system. The combustion chamber of such an engine has all the advantages of an OHV engine, and the gas distribution system is noticeably lighter and does not contain parts that lose rigidity at high speeds or with a sharp change in engine speed.

Motorcycle engines

As you know, internal combustion engines (ICE) are of three types, namely two-stroke, four-stroke and rotary.
The latter are not very common, but some motorcycle manufacturers still use them (Triumf). General structure and operation of the engine

Motorcycles are equipped with internal combustion engines (ICE), in the cylinders of which the thermal energy of burning fuel is converted into mechanical work. The reciprocating motion of the piston, which receives gas pressure, is converted into rotation of the crankshaft through a crank mechanism, which consists of a cylinder, a piston with rings, a piston pin, a connecting rod and a crankshaft. The extreme positions of the piston moving in the cylinder are called dead centers - top dead center (TDC) and bottom dead center (BDC). The distance from TDC to BDC is called the piston stroke, and the space created is called the cylinder displacement (cm3). The total internal volume of the cylinder consists of the working volume and the volume of the combustion chamber. The ratio of the total volume to the volume of the combustion chamber is called the compression ratio; the higher it is, the more efficient the engine's operating process is. Modern engines have a compression ratio of 9–10 units (higher values ​​are found in sports models).

Piston internal combustion engine

For two- and four-stroke internal combustion engines, the workflow and design of parts are somewhat different.

Four-stroke engines

In four-stroke engines, the working cycle occurs in four piston strokes (stroke) and two revolutions of the crankshaft: intake - the piston descends from TDC and sucks in the combustible mixture through the open intake valve; compression - the piston rising from BDC compresses the working mixture with the valves closed; working stroke - the mixture burns, ignited by an electric spark, and the resulting gases, expanding, move the piston down (this stroke of the piston is called the working stroke, since during it useful work is done); exhaust - the upward moving piston pushes the exhaust gases through the open exhaust valve.

Working process of four stroke engine

Two-stroke engines

In two-stroke engines, one power cycle occurs per revolution of the crankshaft. Another feature is the absence of valves (intake and exhaust) with a mechanical drive. Their role is played by the piston itself, opening and closing special windows and channels on the cylinder mirror, and on some engines a reed valve is installed at the inlet. The crankcase volume under the piston is also used for gas exchange.

Working process of two-stroke engine

When the piston moves upward from BDC, the working mixture is injected into the sub-piston space, and in the space above the piston, the exhaust gases remaining from the previous cycle are first displaced, and later, when the windows are closed by the edge of the piston, compression occurs. At TDC, the mixture in the combustion chamber is ignited by an electric spark formed between the electrodes of the spark plug. The burning fuel-air mixture expands and pushes the piston down - a working stroke occurs. Having dropped approximately 2/3 of its stroke, the upper edge of the piston opens the windows in the cylinder. Exhaust gases under excess pressure exit through the exhaust window into the exhaust pipe. Through other windows, fresh charge enters the cylinder from the crankcase cavity, where the descending piston creates excess pressure. This flow of mixture is called purging, and windows and channels are called purging.

Modern two-stroke internal combustion engines have multi-channel (3–7 channels) return-loop purge. In addition, a check plate (petal) valve is installed at the inlet of the cylinder, which is controlled by the vacuum in the crankcase. During inlet into the crankcase (the piston moves from BDC to TDC), under the influence of vacuum in the sub-piston space, the valve plates open the passage of the combustible mixture from the carburetor. When the piston moves back (during purging), excess pressure in the crankcase closes the valve plates, preventing the mixture from being thrown back from the crankcase into the carburetor. The reed valve improves cylinder filling, increases engine power and efficiency, especially at low and medium crankshaft speeds. Many engines also have a special mechanism that changes the height of the exhaust port (and therefore the duration of exhaust) depending on the engine speed (the so-called “controlled exhaust”). Despite the measures taken to improve the gas exchange of two-stroke internal combustion engines, some of the mixture leaves with the exhaust gases, which reduces their efficiency compared to four-stroke engines.

The working process of both two- and four-stroke internal combustion engines occurs in the cylinder. The piston moves along the inner surface (mirror) of the cylinder or insert liner. In modern engines, instead of steel or cast iron liners, carbide nickel-silicon compositions (“Nikasil”) are used, sprayed directly onto the aluminum cylinder base. Depending on the type of cooling system adopted, the cylinder jackets have fins (air cooling) or internal cavities for the passage of coolant.

The piston perceives gas pressure during combustion of the working mixture. It consists of the upper and lower parts (head and skirt, respectively) and the piston pin mounting bosses. The shape of the bottom can be flat or convex; four-stroke engines often have recesses in the bottom for valves. In the piston skirt of two-stroke engines there are cutouts through which the combustible mixture passes, because in these engines the piston controls the gas distribution (intake, scavenging and exhaust).

Pistons of two-stroke (a) and four-stroke engines (b)

1 - piston head; 2 — selections for valves; 3 — compression rings; 4 — oil scraper ring; 5 — piston pin mounting bosses; 6 — piston skirt; 7 — cutout for the purge window; 8 — oil trap cavity (refrigerator); 9 — cutout for an additional purge window

The piston head has thickened walls that house 1–3 compression rings made of special cast iron or steel. These rings seal the gap between the piston and the cylinder mirror and remove heat into the cylinder walls. In four-stroke engines, in addition to compression rings, the piston has an oil scraper ring that removes excess oil from the cylinder bore.

The bosses serve as a support for the piston pin, they have grooves for the retaining ring and holes for oil mist lubrication. Often in the area of ​​the bosses, on the outer surface of the piston, special recesses are made - refrigerators.

The skirt directs the movement of the piston. Due to the unequal thermal expansion of different parts of the piston, its outer surface is given a complex shape: barrel-shaped (conical) in height and oval in circumference. Pistons are made from high-quality aluminum alloys with a high silicon content, which can withstand high thermal and mechanical loads, and at the same time have a low expansion coefficient.

The piston pin pivotally connects the piston to the connecting rod. Typically, a floating pin fit is used in the piston bosses and the upper head of the connecting rod; it is secured from axial movements by spring retaining rings in the bosses.

The connecting rod transmits force from the piston to the crankshaft and consists of a rod (I-beam or elliptical section) and heads: upper and lower. Depending on the type of engine and the lubrication system used, the connecting rod heads are made with plain bearings (with bushings or liners) or rolling bearings (roller, needle). When a plain bearing (liner) is used in the lower head, the head itself is detachable. In the case of using a needle bearing, the head is made one-piece and the lower journal of the shaft is pressed into the cheeks.

Connecting rods

a - with a detachable lower head (“Dnepr”); b - with a one-piece lower head (“Ural”); 1 — connecting rod cover; 2 — connecting rod bolt; 3 — connecting rod; 4 — bearing separator of the lower head of the connecting rod and rollers; 5 — liners

The crankshaft receives force from the piston (via the connecting rod), converts it into rotational motion, and then transmits the torque to the transmission. In addition, other systems and mechanisms are driven from the crankshaft: gas distribution mechanism (GRM), oil pump (in four-stroke internal combustion engines), generator, cooling system pump, balance shafts. Depending on the number of engine cylinders and the design design, the crankshaft may have one or more elbows, each of which is formed by two cheeks and a connecting rod journal. Between the knees and along the edges of the shaft there are main journals supported on bearings.

Crankshafts are made composite or non-separable (one-piece). The type of bearings of its supports (main journals) depends on the lubrication system used. To improve the smooth operation of the engine (after all, only one stroke of the piston is working, and the rest - one for a two-stroke engine, and three for a four-stroke engine - require energy expenditure), the crankshafts have an external flywheel, massive cheeks and counterweights. In addition, many modern engines have special balance shafts driven by a gear train from the crankshaft.

Crankshaft of two-cylinder engine

b - solid (“Dnepr”); 1 — connecting rod with a one-piece lower head and a roller bearing; 2 - counterweight;

3D Motorcycle Engine

Four-stroke internal combustion engine. How it works?

Disassembling the Honda CBR929RR engine (part 1). The first part of a scary video of disassembling the engine of a Honda CBR929RR motorcycle. Someone has taken up residence in the engine and is growling, rattling, knocking. The bastards decided to find out who lives there and drive him out. To do this, we unscrewed all the attachments: covers, generator, drives, etc. The closer you get to “Alien”, the scarier it is...

The engine crankcase is made one-piece or with a split plane (longitudinal, transverse). In four-stroke engines, the crankcase (or sump) is usually a reservoir for oil draining from lubricated parts. Many engines share a common crankcase with clutch and gearbox. In two-stroke multi-cylinder engines, the crankcase volume of each cylinder must be separated from the others; this complicates the design of the crankcase when there are two or more cylinders.

Gas distribution in four-stroke internal combustion engines is controlled by a camshaft (or camshaft), which rotates twice as slow as the crankshaft. When rotating, the camshaft, with its protrusions (cams), interacts with pushers, which directly or through a transmission link (rocker arm, rocker) open the valves (intake and exhaust); their closure occurs under the action of valve springs. The periods of time when the intake and exhaust valves are open are called valve timing; they are coordinated with the piston strokes.

Valve timing diagram of a four-stroke engine

1 - opening of the intake valve; 2 - closing the intake valve; 3 - closing the exhaust valve; 4 — opening of the exhaust valve; angle “a” - valve overlap

To better fill the cylinder with the combustible mixture, the intake phase begins when the piston has not yet reached TDC. As the piston continues to move from TDC to BDC, it sucks in the combustible mixture through the open valve; they complete the intake after passing BDC, when part of the mixture enters the cylinder by inertia. Cleaning the cylinder from exhaust gases also begins at the end of the expansion stroke, when the piston has not yet reached BDC, but there is excess pressure in the cylinder. Then, as the piston moves from BDC to TDC, the piston pushes out the exhaust gases. The exhaust valve is closed after TDC to allow some of the exhaust gases to leave the cylinder by inertia. Thus, there is a period of time when both valves are open - this is called "valve overlap". Each four-stroke engine model has its own optimal valve timing, which is set at the factory by the profile of the camshaft cams. Some newer motorcycle engines have special devices that allow the valve timing to be changed depending on the crankshaft speed.

Modern four-stroke internal combustion engines use several types of timing belts: OHV, OHC, DOHC.

Schemes of gas distribution mechanisms

In the OHV design, the valves located in the cylinder head are driven from the “bottom” camshaft via pushrods, rods and rocker arms; the design does not ensure smooth operation of the mechanism at high crankshaft speeds. Engines with an OHC timing belt have an “overhead” camshaft that acts on the valve lifters through levers (rockers); the shaft is driven by a chain or toothed belt. Modern multi-valve heads with 4-5 valves per cylinder use two camshafts, each of which directly acts on the valve lifters with its cams (DOHC design). This design has a minimum of parts and, because of this, the inertia of the valve drive is reduced, which makes it possible to increase the engine crankshaft speed, and hence its power; DOHC type timing belts are becoming increasingly widespread.

OHV operation diagram

The camshaft is driven from the crankshaft by a gear, chain transmission or by means of a toothed belt. In the last two cases, the engines have chain (belt) tensioners and dampers.

For normal operation of the valve mechanism, there must always be a thermal gap (0.05–0.15 mm) between the valve stem and its drive. When there is no clearance, the valves do not close tightly, as a result of which they burn and fail. With an increased gap, they do not open completely (power is lost) and, in addition, they knock. Many engines of foreign motorcycles have timing belts with hydraulic compensators (operated by pressure in the lubrication system), which automatically maintain the required valve clearances. If such a system is not provided, the gap is adjusted during maintenance.

Four-stroke engines are structurally more complex than two-stroke engines, since they have an additional timing belt and lubrication system. However, since the 70s of the twentieth century, they have been predominantly used on motorcycles due to cleaner combustion and better efficiency. Currently, in developed countries, motorcycles with two-stroke engines have limited use - these are older models, sports motorcycles and mopeds; In the foreseeable future, particularly in Europe, the production of these engines is expected to cease completely due to the extremely negative impact on the environment.

Motorcycle engines most often have 1, 2 and 4 cylinders, although there are 3, 6 and even 10 cylinders. They have a variety of layouts: in-line (longitudinal and transverse), V- and L-shaped, horizontal opposed. The engine displacement of serial motorcycles usually does not exceed 1500 cm3, power is 150–180 hp.

Arrangement of cylinders in modern motorcycle engines

Engine lubrication and cooling systems

Lubrication of internal combustion engine parts is necessary to reduce friction between them and remove heat. It is carried out by motor oils that are resistant to high temperatures combined with low viscosity at low temperatures (for reliable engine starting). In addition, motor oils should not form carbon deposits during combustion and should not be aggressive towards rubber seals and plastic parts. Mineral oils (obtained from petroleum by distillation), semi-synthetic and synthetic oils are used for lubrication. Semi-synthetic oils are a mixture of high-quality petroleum and synthetic base components. Synthetic oils do not have a petroleum base; due to effective anti-friction additives, the service life of the engine is increased (compared to mineral oils), and it is easier to start at low temperatures. Despite the higher price, semi-synthetic and synthetic oils are increasingly used. Special motor oils are produced, and they differ for engines that differ in stroke (two- and four-stroke) and in the degree of boost. For Russian motorcycles with four-stroke engines, automobile oils of various viscosities are used, for two-stroke engines - MGD-14, or foreign analogues.

In four-stroke engines, three methods of supplying oil to friction surfaces are used: under pressure, splashing and gravity. Most friction pairs are lubricated under pressure generated by the oil pump. Other friction pairs are lubricated by oil mist, which is formed when oil droplets splash on the moving parts of the crank mechanism. And finally, the third group of parts is lubricated with oil flowing through special channels and gutters. The crankcase (sump) is usually an oil reservoir (the so-called “wet” crankcase - Fig. a).

Four-stroke engine lubrication systems

Some foreign motorcycles have a system with a “dry” sump (Fig. b), from which oil is first pumped out by one of the pump sections into a separate oil tank, and supplied under pressure to the friction surfaces by the other section. The tank can be located in different places: near the engine, at the rear wheel or in the front of the frame.

The oil level in all lubrication systems is controlled using a dipstick (with minimum and maximum level marks) or through a special inspection hole. Operating the engine with a low oil level is unacceptable.

The lubrication system contains an oil pump, an oil filter, valves (return and safety) and lines in the form of channels (tubes, drillings in parts).

Oil pumps for four-stroke internal combustion engines are of plunger and gear types.

Types of Oil Pumps

a - plunger; b - gear with external gearing; c - with internal gearing

The most widely used gear pump The gears are driven into rotation by the engine crankshaft or camshaft. The oil enters the inlet cavity of the housing, is captured by the gear teeth and is pumped to the outlet cavity. The most common filters are replaceable paper ones.

In two-stroke engines, the rubbing pairs are lubricated by oil present in the form of small droplets in the fuel vapor. Oil is mixed with gasoline either first in the tank (in a ratio of 1:25–1:50), or directly in the inlet pipe, where it is supplied in the required quantity by a special metering pump. The latest oil supply system is called a “separate lubrication system”; it is predominantly used on foreign two-stroke engines. In such systems, the oil supply at low loads is brought to a ratio of 1:200, which reduces exhaust smoke, reduces overall oil consumption and the formation of soot in the combustion chamber.

Two-stroke engine with separate lubrication system

1 - oil tank; 2 - carburetor; 3 — throttle cable separator; 4 — throttle handle; 5 — oil supply control cable; 6 — plunger dosing pump; 7 - hose supplying oil to the inlet pipe

Separately lubricated systems use plunger-type pumps driven by the crankshaft or engine transmission. The oil is stored in a special tank and flows to the pump by gravity. The design provides a low oil level indicator in the tank. The amount of oil supplied to the inlet pipe depends on the engine speed; in some designs there is another adjustment of its performance - from the position of the throttle handle, for which the pump is connected to it by a separate cable.

Cooling system

When fuel burns in an internal combustion engine cylinder, heat is released, part of which (about 35%) goes to useful work, the rest is dissipated into the environment. If heat dissipation is not effective enough, the parts of the cylinder-piston group overheat, and due to their excessive expansion, as well as violation of lubrication conditions, jamming and damage to the parts may occur. To prevent overheating, all motorcycle engines, regardless of stroke, have a cooling system - air or liquid.

Cooling systems for motorcycle internal combustion engines

Classic version device

As a rule, the classic motor for a walk-behind tractor is a single-cylinder 4-stroke internal combustion engine. Most of them are air cooled.

The engine is equipped with the following operating systems.

• Starter (starting mechanism) - designed to spin the crankshaft and give it the desired speed.
• Fuel supply system is a set of devices involved in preparing the fuel-air mixture. This includes the fuel tank, hose, carburetor, air filter.
• The ignition system is a set of parts that create the spark necessary to ignite the fuel-air mixture in the combustion chamber.
• Lubrication system - serves to supply oil to parts to prevent them from rubbing against each other.
• Cooling system - exists to remove heat from the cylinder block. When the crankshaft rotates, the flywheel impeller creates a flow of air, as a result of which it cools.
• Gas distribution mechanism - is responsible for the constant flow of air-fuel mixture into the cylinder through the nozzles.

But each model of a Chinese motor for a walk-behind tractor has several differences.

New technologies according to the old principle

Ever since the four-stroke engine was invented, it has been constantly improved.

There have also been changes in the food system. Modern engines no longer use a carburetor - injectors and electronics are everywhere.

To improve the filling of combustion chambers with air, pressurization systems are used. This allows you to increase power with a small volume, as well as reduce fuel consumption.

But with all this, the principle of operation of the internal combustion engine remains the same as it was.

Popular Chinese motors

Chinese motors are usually used in budget vehicles. The most reliable manufacturers of units are Lifan and Zongshen; they produce high-quality analogues of the Japanese brand Honda GX at a lower price.

Model 160F

The gasoline engine for walk-behind tractors type 160F is designed for light walk-behind tractors used in everyday life. It is economical, budget and low-power - 4 liters. With.

• single cylinder, 4 stroke, OHV;
• air cooling;
• electronic ignition;
• launch is performed by the manual start system;
• easy to use: compact dimensions, easy start;
• There is an oil level sensor.

Working volume – 120, fuel tank capacity – 2 liters. Created according to the Japanese model of the Honda GX120.

Model 168F

168F is the most commonly used model in walk-behind tractors. The design of this motor is simple and reliable. Engine power – 5.5 l. pp., working volume – 163

Features of the Chinese 168F engine:

• starting only with a manual starter;
• OHV – arrangement of valves in the cylinder head;
• It is possible to equip it with an oil level sensor and a light winding for the generator - depending on the manufacturer.

This type of motor is produced under the brands Lifan, Zongshen, Loncinu and others.

Model 170F

170F is a Chinese gasoline engine with overhead valves and a cast iron cylinder liner, which is excellent for walk-behind tractors. This unit is a variation of the 168F model, only it is more powerful - 7 hp. With.

• working volume – 212;
• the starter is manual, but it is possible to connect an electric starter;
• light weight (16 kg), compact dimensions.

The motor is vibration-resistant, quiet in operation, and operates without interruption in harsh weather conditions.

Model 177F

The 177F is a heavier and more powerful engine than the previous model. The unit is modeled after the Honda GX270.

• economical fuel consumption;
• low noise level;
• working volume – 270;
• power – 9 l. With.;
• fuel tank with a volume of 6 liters;
• weight – 25 kg.

Suitable for heavy walk-behind tractors used in agriculture. Easy to transport.

Model 182F

182F – single-cylinder gasoline 4-stroke engine with increased power, 11 hp. With. This is a budget analogue of the Honda GX340 unit.

• economical fuel consumption;
• low noise level;
• modest dimensions.

Working volume – 337. 182F is the most powerful engine in the line that can be installed on a walk-behind tractor.

Model 170F (A), 170FE, 170FS

Unlike previous units, this engine is diesel. Engine power is 4 liters. s., and the working volume is 211.

The cost of these models is higher than gasoline ones, because they have a significantly longer service life. This is achieved by lubrication of the crankshaft under pressure.

The index E in the name of the device indicates the presence of an electric starter.

Oldsmobile Rocket

Oldsmobile Rocket 88, in addition to an excellent engine, boasted a 3-speed automatic transmission

Bottom valve engines, or as they were also called engines with side valves, had several problems. First of all, this is low specific power and high fuel consumption. In addition, large and heavy SV engines became increasingly difficult to fit under the hood of new post-war models. Oldsmobile engineer Gilbert Burrell understood this very well and in 1945, he began developing an overhead valve V8 on his own initiative.

Meanwhile, another division of General Motors, Cadillac, also launched a similar project. Ultimately, Burrell's design won out. Not least because of GM's desire to maintain the image of Oldsmobile as the most advanced company in the group.

1949 Oldsmobile Rocket

Be that as it may, the new V8 engine turned out to be very successful. It received a volume of 303 cubic meters. inches and a power of 135 hp. Placing valves in the cylinder head allowed engineers to significantly improve cylinder filling, and therefore power and efficiency. In addition, its compression ratio of 7.5:1 was significantly higher than that of any lower valve engine of those years.

In 1949, the engine was introduced in the flagship Oldsmobile 98, and two months later in the lighter Oldsmobile 88.

Criterias of choice

When choosing an engine for a walk-behind tractor, you should pay attention to several characteristics. First you need to decide on the type of engine.

Walk-behind tractors use both gasoline and diesel units. The table shows their advantages:

• easier to use;
• start faster;
• suitable for use in different weather conditions;
• cheaper.

• withstand heavy loads;
• use fuel more economically;
• have a greater margin of safety.

The second criterion when choosing a Chinese engine is power:

• On a light walk-behind tractor it will be enough to install a device with a power of up to 4 liters. With.;
• medium ones require an engine with 4–7 liters. With.;
• for heavy walk-behind tractors, a 7 hp unit is required. With. and more.

You also need to pay attention to the following characteristics:

• Crankshaft output. The most common ones are with a key, and those often used are with a splined exit. Less commonly used is a conical shaft overhang.
• Oil level sensor. This will prevent damage to the device.
• The presence of an electric starter will make it much easier to start the engine when it comes to gasoline units. Diesel engines are more suitable for manual starting.
• Air filter. It comes with an oil bath and double cleaning.
• Motor resource . Models where this criterion reaches 3000 operating hours or more are recommended.