Novice drivers sometimes think that the most important quality that motorcycle engines have is the amount of horsepower, and they believe that the vehicle will ride well only with more than a hundred power. However, in addition to this indicator, there are many characteristics that affect the quality of the motor.
Types of motorcycle engines
There are two-stroke and four-stroke engines, the principle of operation of which is somewhat different.
Also on motorcycles set a different number of cylinders.
In addition to the native carburetor engine, injection units can often be found. And if motorcyclists are used to fixing the first type on their own, then an injection engine with a direct injection system with their own hands is already problematic to repair. For a long time already produce diesel motorcycles and even with an electric motor. The article will examine the characteristics of a carburetor-type motorcycle engine.
How the engine works
In the engine cylinders, the thermal energy of the burning fuel is converted into mechanical work. In this case, the piston moving due to gas pressure causes the crankshaft to rotate through the crank mechanism. This mechanism consists of a crankshaft, connecting rod, piston with rings, piston pin, cylinder.
Differences in design lead to different operation of a two- and four-stroke engine.
Four stroke engine
Such motors have a duty cycle of four strokes of the piston and two turns of the crankshaft. The engine diagram clearly shows the device of the piston ICE and its working process.
At the inlet, the piston descends from top dead center, sucking the mixture through an open valve.
When compressed, the piston rising from the bottom dead center compresses the mixture.
During the working stroke, the mixture, ignited by an electric candle, burns out, and the gases move the piston down.
When released, the piston, rising, pushes the exhaust gases through an open exhaust valve. When he reaches the top dead center again, the exhaust valve closes and everything repeats again.
The advantages of four-stroke are:
The design of this type can display the following engine diagram.
Two stroke engine
The engine capacity of this type of motorcycle is usually less, and the duty cycle takes one revolution. In addition, there are no inlet and outlet valves. This work is reproduced by the piston itself, which opens and closes channels and windows on a cylindrical mirror. Also, during gas exchange, crankcase is used.
The advantages of this engine are:
with the same cylinder volume, it has a power exceeding the four-stroke by 1.5-1.8 times;
does not have a camshaft and valve system;
manufacturing is cheaper.
Cylinders and the workflow in them
The working process of one and the other engine takes place in the cylinder.
The piston moves here along a cylindrical mirror or insert sleeve. If air cooling works, then cylindrical shirts have ribs, and with water cooling they have internal cavities.
The crankshaft through the connecting rod perceives the movement of the piston, transforming it into rotational, and then transmitting the transmission torque. Also, the gas distribution mechanism, pump, generator and balancing shafts begin to work from it. The crankshaft has one or more elbows depending on the number of cylinders.
In a four-stroke engine, so that the cylinder is better filled with mixture, the inlet begins before the piston reaches top dead center, and ends after it passes the bottom dead center.
Its cleaning begins even before reaching the bottom dead center, and the exhaust gases are expelled when the piston moves to the top dead center. After that, the exhaust valve closes so that the gases leave the cylinder.
The following types of gas distribution mechanism are used on this type of motor:
In the latter type there is a minimum number of elements, so that the crankshaft can rotate faster. Therefore, DOHC is becoming more common.
Four-stroke engines have a more complex design compared to two-stroke ones, since they have a lubrication system and a gas distribution mechanism that is not available for two-stroke engines. However, they have become widespread due to cost-effectiveness and less harmful effects on the environment.
Motorcycle engines are most often single-, double- and four-cylinder. But there are units with three, six and ten cylinders. In this case, the cylinders are in-line - longitudinal or transverse, horizontal opposed, V-shaped and L-shaped. The working volume of engines usually have no more than one and a half thousand cubic meters of these motorcycles. Engine power - from one hundred and fifty to one hundred and eighty horsepower.
Engine oil
Lubrication is necessary so that excessive friction does not occur between the parts of the motor. It is realized with the help of motor oils having a stable structure from the effects of high temperatures and low viscosity at low rates. In addition, they do not form carbon deposits, are not aggressive to plastic and rubber parts.
Oils are mineral, semi-synthetic and synthetic. Semi-synthetics and synthetics are more expensive, but these types are preferred more, since it is believed that they are more useful for the engine. Different types of oils are used for two-stroke and four-stroke. They also differ in the degree of forcing.
Wet and dry sump
Four-stroke engines use three methods of oil supply:
gravity;
spatter;
pressure feed.
Moreover, most of the rubbing pairs are lubricated under pressure from the oil pump. But there are those that are lubricated by oil fog, resulting from the spraying of the crank mechanism, as well as parts to which oil flows down the channels and gutters. In this case, the oil pan serves as a reservoir. He is called in this case "wet."
Other motorcycles have a “dry” crankcase system, where in one section the oil is pumped into the tank and the other is supplied under pressure to the friction points.
In gunners, lubrication occurs with oil, which is in the fuel vapor. It is mixed with gasoline in advance, or in the inlet pipe it is supplied by a metering pump. This latter type is called the “separate lubrication system”. It is especially common on foreign engines. In Russia, the system is part of the Izh Planet 5 and ZiD 200 Courier motorcycle engine.
Cooling system
When the fuel in the engine burns out, heat is released, of which almost thirty-five percent goes into useful work, and the rest is dissipated. Moreover, if the process is ineffective, the parts in the cylinder overheat, which can lead to their jamming and damage. To prevent this from happening, a cooling system is used, which can be air and liquid, depending on the type of motor.
Air cooling system
In this system, parts are cooled by oncoming air. Sometimes, for better performance, the surfaces of the cylinder of its head are made ribbed. Forced cooling is sometimes used with a mechanical or electric fan. Four-stroke engines also carefully cool the oil, for which the crankcase surface is increased and special radiators are installed.
Liquid cooling system
The option is similar to what is installed on cars. The coolant here is antifreeze, which is low-freezing (from minus forty to minus sixty degrees Celsius) and high-boiling (from one hundred twenty to one hundred thirty degrees Celsius). In addition, antifreeze and lubricating effect is achieved by antifreeze. Pure water in this capacity cannot be used.
Overheating of the cooling system can be caused by overloading or contamination of surfaces that remove heat. Also, individual elements may break down in it, due to which liquid will leak. Therefore, the cooling operation must be constantly monitored.
Supply system
As fuel for carburetor motorcycles, gasoline is used, the octane number of which is not lower than 93.
Motorcycle engines have a power system, which includes a fuel tank, crane, filter, air filter and carburetor. Gasoline is located in the tank, which in most cases is installed above the motor in order to flow by gravity into the carburetor. In other cases, it can be supplied using a special pump or vacuum drive. The latter can be found on two-stroke.
The fuel tank has a lid with a special hole where air enters. In many foreign motorcycles, however, air enters through coal tanks. And some have a lock on the lid.
Thanks to the fuel valve, fuel leakage is prevented.
Air enters the carburetor through an air filter. The filter is of three types.
In the compact oil type, air enters the center, rotates 180 degrees and passes into the filter. At the same time, it is cleaned by turning the flow, where heavy particles settle in the oil. The Ural and Izh motorcycle engine is equipped with such a filter. However, other types of paper and foam rubber are used abroad.
Paper filters are disposable. They must be changed at every maintenance.
Reusable foam filters - they can be washed and re-impregnated with oil.
Sports motorcycles, with an engine of 250 cubic meters and above, today have a system of so-called “direct intake”, when air intake takes place in front of the fairing, so that the filling of cylinders at high speeds increases.
Carburetor and its types
This device prepares and doses the air-fuel mixture, which after it passes into the cylinder. Modern carburetors come in three types:
spool;
continuous depression;
register.
All domestic engines, as well as the engine of the Ural motorcycle, have spool carburetors. The only exception is Ural-Vostok, on which a constant-pressure carburetor is installed.
In the spool carburetor, the throttle stick is connected to the spool. Through exposure to it, the air entering the motor is regulated. A cone needle is connected to the spool, which enters the atomizer. When it changes, the mixture is enriched or depleted. A fuel nozzle is installed on the sprayer. And together, all the elements make up the dosing system.
In carburetors of constant rarefaction, the movement of the gas handle is transmitted to the throttle, which is closer to the outlet of the carburetor. The air in the chamber above the spool interacts with the mixing carburetor chamber. It turns out that the movement of the spool is regulated by discharge in the intake tract.
Register carburetors, which are equipped with many foreign single-cylinder four-stroke engines, for example Honda engines, combine the two previous types. It has two mixing chambers, where in one the spool is driven from the handle, and in the other from vacuum in the mixing chamber.
Launch
In order to start a cold engine, an enriched mixture is needed. In the chamber of some carburetors for this there is a float drowner. When its rod is pressed, the fuel level in the chamber rises sharply to a level above the permissible level. Because of this, fuel begins to flow into the intake manifold. And part of the fuel flows out. For some time, however, the design of carburetors is performed in such a way that the fumes do not fall out. Such designs involve the use of an enrichment mixture, which is an air damper or another fuel channel. It is used instead of the drowner.
Recently, four-stroke motorcycle engines often have an electric fuel injection system. It consists of a fuel pump with electric drive, battery, electromagnetic injectors, electronic control unit, which is connected to various sensors, distribution pipe.
There are also motor control systems, where the adjustment of the power and ignition systems are combined, which increases the efficiency and at the same time the power of the unit.
The main malfunction of the power system, due to which it may be necessary to repair the engine of the motorcycle, is to reduce or even stop the supply of fuel due to blockage. To avoid this, use a fuel filter. In addition, it is necessary to monitor the condition of the air filter and the tightness of the nozzles.
Exhaust system
The exhaust system consists of a cylindrical exhaust channel, a pipe and a silencer. In two-stroke engines, efficiency and power directly depend on the size and shape of the system parts. Therefore, they use exhaust systems on each cylinder separately. They have a resonator, a nozzle and a blanking nozzle.
For four-stroke engines, the valves are controlled by the gas distribution system, so resonance does not play a special role in them. In them, usually all pipes are reduced to a single muffler.
On some motorcycles, the outlets are equipped with catalytic converters that reduce emission toxicity (they are installed, for example, on Honda engines and other Japanese manufacturers). Such devices have been developed due to stricter exhaust gas requirements in the EU, USA and Japan. In order to prevent the reverse ejection of the mixture from the cylinders at idle and low rotation of the crankshaft, special power valves are provided in the exhaust systems of many motorcycles.