Not every motorcyclist has the ability to take care of his or her own equipment. Usually, many people prefer to leave it for repair and maintenance in the hands of reliable professionals, remaining in a blissful ignorance.

Unfortunately, on the road the breakdowns happen without warning and most often at the most inopportune time, even with quality and timely serviced equipment.

Exactly in such cases people start to regret the absence of at least some idea about the work of their iron horse, which would allow them to suggest the cause of the breakage and the direction of actions to eliminate it.

This page is not intended to make you professional mechanics, but it can give you a good idea of the structure and operation of the basic components of a motorcycle or scooter.

The modern motorcycle is the result of years of continuous work to improve performance, which has made the motorcycle complex and intricate. However, it often turns out that what looks complicated is nothing more than a set of relatively simple parts connected to each other.


The engine generates the energy required to propel the motorcycle. The main parts and assemblies include the cylinder head, cylinder (ry), piston (ny), connecting rod (ny), and crankshaft. All internal combustion engines (ICEs), except rotary engines (RCEs), have these parts; the main difference between engines is the number of cylinders, pistons, and their arrangement. In almost all modern designs, engine parts are inside or attached to a cast housing. These housings are commonly referred to as crankcases (crankcases), despite the fact that they contain more parts than a single crankshaft.

All internal combustion engine designs share the need for precise control of the flow rate of the fuel-air mixture entering the case. Here we consider the processes of mixing the fuel and air in the correct proportions, feeding this mixture into the cylinder(s) at a volume corresponding to a given engine speed, and venting the exhaust gases after combustion is complete. Although it is common practice to separate the operation of the intake and exhaust systems, it is useful to consider them together as a process in which fuel energy is extracted and converted into useful work, and then the byproducts of heat and noise are removed.

Ignition system

The engine requires some method of initiating combustion at a strictly defined moment of each operating cycle. The most common method is the use of a momentary high voltage spark. The high-voltage spark travels from the insulated electrode in the center of the spark plug to the ground (ground to ground) through a small air gap. The essential elements of any ignition system include the following. First, a way must be found to obtain electrical power to power the system Even though in many cases the power source is the battery, it must be ensured that it is recharged, otherwise the system will soon stop working due to the battery being discharged. Power from the battery or from a separate power winding is supplied to the ignition coil. This device converts a low voltage, high current (‘low voltage’) into a high voltage, low current (‘high voltage’) which is necessary to produce the spark on the electrodes.In modern systems we usually have to talk about a conversion of 12 volts to about 40 kilovolts. To control and change the spark formation torque, some kind of mechanical type switch in the form of a contact breaker or its electronic analogue – an inductive sensor, or a crank angle sensor in combination with an electronic control unit (ECU) is required. In addition, a method of changing the ignition timing (leading and lagging), which mechanically or electronically optimizes the ignition timing at all engine speeds, is required. The basic theories, principles and methods related to spark formation and ignition timing control are discussed here


All motorized two-wheeled vehicles need a device to transmit power from the engine to the rear wheel. This function is performed by a ‘power transmission’ or ‘transmission’. There are two main types of transmissions: manual and automatic: they differ in the level of intervention and control allowed to the driver. Manual transmissions are used on all modern production motorcycles, and in the past were used on some mopeds. Automatic transmissions are mostly found on mopeds and scooters, although there are examples of automatic transmissions used on production motorcycles (Honda DN-01).

All types of transmissions, both manual and automatic, have a front gear, clutch, gearbox, and main gear, although their shape can vary depending on the type of machine. In a conventional manual transmission, the front gear transmits power from the crankshaft through the clutch to the gearbox. The clutch is used to connect and disconnect the engine and gearbox, thus allowing the engine to run while the car remains stationary. The gearbox allows a choice of different gear ratios to achieve maximum performance within the engine’s range of speed, power, and torque. The main gear transmits power from the transmission to the rear wheel.

All types of transmissions are designed to keep the engine running within a narrow speed range (measured in revolutions per minute), while providing the machine itself with a relatively wide range of driving speeds. This is because, although a sufficiently wide range of speeds is possible, the most efficient operation is only achieved in a narrow range of speeds. In order to provide a wide range of speeds, different gear ratios between the engine and the rear wheel are required when the engine is operating in a narrow speed band. In its most simplified form, the work of a one-speed automatic scooter transmission is not particularly difficult, while much more complex and sophisticated systems are used on larger machines. Much depends on the purpose of the machine in question and the performance expected of it. A small volume scooter is required to simply move the driver over short distances with moderate speeds, to be cheap to buy and operate: therefore, a complex transmission scheme is not required. On larger machines, the range of speeds required, the distances they cover, and the weight of the load carried is much greater, this requires a transmission with multiple gear ratios.

Engine lubrication and cooling system

In order to reduce friction, the internal moving parts of the motor are manufactured with high precision and surface cleanliness. When viewed under a microscope, what appear to be smooth surfaces are actually quite rough, and to reduce the friction and heat generated by surface contact, a film of lubricant must be introduced to separate the contacting surfaces with it. By maintaining a film of oil on the various engine parts, the lubrication system effectively keeps the rubbing surfaces apart. If the lubricant layer is disturbed at any point, there is a rapid and localized increase in temperature. In the extreme case, this can lead to seizure of the damaged surfaces by welding them together.

In addition to its primary role of lubrication, oil performs many secondary functions. An oil film coats all internal parts, thus avoiding contact with air and acids that can cause corrosion. In four-stroke engines with permanent oil recirculation, it removes all kinds of dirt particles and wear products, which are then picked up by the oil filter so the engine is cleaned. It also enhances the tightness between the piston and rings and, on two-stroke engines, between the valve paddles or disc valves and the crankcase. Finally, it helps to dissipate heat from heated surfaces: piston, rings, cylinder walls, which are subject to high local temperatures.

Despite the high efficiency of modern engines, fuel and oil, the problem of heating remains. Ideally, the engine would convert all the energy contained in the fuel into useful power and there would be no mechanical friction, so that it would remain cold. In practice, all engines have a high level of unwanted heat generation, which must be kept within reasonable limits to prevent damage.

This can be achieved directly by radiating heat into the ambient air (air cooling), or indirectly by dissipating heat into the coolant, which cools itself in the radiator (liquid cooling).

Wheels, tires and brakes

Taken together, wheels, tires, and brakes are probably the most important safety-related parts. Any one of them performs multifaceted tasks in the most unremarkable way possible.

Wheels support the motorcycle, ensure that the tires are mounted accurately and securely, and resist the loads applied to them during braking, acceleration, or from uneven road surfaces. In addition to the above, the wheel should be as light as possible. Based on needs, wheel designs have evolved to meet the ever increasing demands placed on them with the gradual increase in engine power.

Tires are much more complicated than one might think: they, too, have evolved with the motorcycle into those challenging products that are now considered commonplace. Tires are supposed to provide safe and reliable motorcycle operation over a wide range of loads, speeds, temperatures and weather conditions. They form the basis of rider safety, but their price must be kept within reasonable limits, as tires are more of a consumable item.

Brakes are supposed to ensure that the stored energy of a large, fast-moving motorcycle and its driver is absorbed within seconds. Brakes convert that energy into heat and dissipate it quickly, a fact that rarely crosses a driver’s mind while driving.

Front suspension and steering

Any type of suspension serves to absorb road surface irregularities while maintaining constant contact between the wheels and the road, and to insulate the motorcycle and its rider from the effects of these irregularities. This requires a unit that can compress and stretch, in this case a spring is ideal for this purpose. However, springs have a tendency to oscillate relative to their natural state as a result of their compression and stretching. Using springs without additional devices would result in a very uncomfortable ride. In order to control the vibrations, some way of damping them would be required, the best medium for this might be oil.

Over the years, manufacturers have tried rubber, torsion blocks and torsion bands instead of springs. Torsion blocks are still used in the connection of the drive units of some lawnmowers. However, rubber is very easily damaged. Gas was also used and continues to be used on some machines in conjunction with springs. Gas-filled suspensions have the advantage of being easy to adjust (increasing pressure increases suspension stiffness and vice versa) and providing a natural “progressive response” (as gas is compressed, resistance on its side increases). With gas, there is the problem of sealing, and the problem that changing temperatures with atmospheric changes or operation causes a change in pressure that changes “stiffness”.

So in most cases the combination of springs and hydraulics is the most popular: the question is how to position it all in conjunction with steering. Over the years, there have been many different designs that can be classified into four main categories: telescopic fork, push/pull lever fork, car-type lever suspension, and parallelogram fork. The steering scheme commonly used on most motorized two-wheeled vehicles is “inherited” from the bicycle and consists of a tube connected to the front wheel that pivots relative to the frame to make a turn. The differences in design are due to differences in the suspension arrangement, but they are minor, and in any case the principle of operation remains the same.


Regardless of the type of front suspension, steering always begins with the steering wheel, which pivots relative to the frame and is connected to the front wheel so that turning the steering wheel will cause the wheel to move.

Unsprung masses

The mass of all components is divided into the mass of components supported by the suspension, which is called “suspension mass”, and the mass of other components not supported by the suspension, which is called “unsprung mass”. It should be noted that the tires also absorb some of the bumps, and from this point of view we can say that the entire mass of a motorcycle is sprung.

To understand the term unsprung mass, imagine a motorcycle taken off the stand and sitting upright. When a person sits on the motorcycle, the springs are compressed when loaded by the weight of the rider. All of the motorcycle assemblies that move, when the rider sits down and the springs compress, are sprung masses, they move with the suspension (fuel tank, seat, frame, engine, etc.). All units that do not move are unsprung masses (wheels, tires, brakes, etc.). This raises the question: are the masses of the suspension arms, shock absorber and forks the unsprung masses or the unsprung masses? For the sake of simplicity, it is assumed that the part of the suspension arm behind the shock absorber mounting point is the unsprung mass, and the part in front of the mounting point, that is, between the mounting point and the axis of rotation of the arm, is the unsprung mass; the lower half of the shock absorber is unsprung and the upper half is sprung; the outer fork tube or movable tip is unsprung and the inner or fixed tube is sprung.

Why is low unsprung mass important?

When a motorcycle hits a bump, the unsprung assemblies gain momentum as they begin to move; the amount of this momentum is proportional to the unsprung mass. The impulse created by the unsprung assemblies increases the load on the suspension and requires stiffer suspension springs to counteract it. At the same time, more force is transferred to the unsprung assemblies of the motorcycle by the springs, affecting their performance. A similar situation occurs when unsprung units hit a pothole.

To ensure perfect suspension performance, there must be no unsprung masses, but this, of course, is impossible. The point is to reduce the unsprung masses relative to the sprung masses as much as possible, because this ratio is more important than the unsprung masses themselves. On a motorcycle like the Honda Goldwing, this ratio is good because it has a very large mass of unsprung components, much larger than on many motorcycles; yet the unsprung masses are about the same as on other large bikes. However, on a sportbike, the masses tend to be kept to a minimum, and it is difficult to maintain a good ratio with traditional wheels and other unsprung components. The only way to solve this problem is to use exotic and expensive lightweight materials like magnesium or carbon fiber.

Rear suspension

Rear suspension on motorcycles first appeared relatively recently. While the need for front suspension became apparent almost immediately, things were much less critical with rear suspension-until speeds increased. For decades, parallelogram forks worked in conjunction with rigid rear-wheel suspension (known by many as a hardtail), and the biggest bumps in the road were softened by the suspension of a single seat. The passenger had to put up with the basic cushion above the rear fender and with it most of the shock and vibration transmitted by the rear wheel.

Shortly after World War II, the lack of rear suspension became a serious problem for racing motorcycles because the time the rear wheel was out of contact with the road also increased due to increased speeds. This meant that the lack of suspension began to limit the overall performance of the machines.

One of the first to appear was the candlestick type rear suspension. It consisted of little more than a pair of double-ended upright springs. located on either side of the frame between two special rear fork brackets. The wheel axle was positioned between these and secured between the upper and lower springs. Despite the lack of cushioning, candle suspension frames provided a certain level of comfort and handling, and they soon became widely used on road models. Some of the major drawbacks of this type of suspension are wear (hence the tendency for the wheel to twist relative to the frame due to the lack of linkage between the fork ends) and insufficient suspension travel, which is limited by the chain tension when the wheel is shifted vertically to either side from the center position; this also means that the chain will have the weakest tension in the center position. Introduced by Triumph in the ’50s, the sprung hub was essentially a further development of the rear suspension. A spring mechanism was located inside the rear hub and provided suspension to the rear wheel axle. This trim gave the suspension some limited travel compared to the rigid rear wheel suspension.

The real breakthrough in rear suspension came with the advent of the oscillating rear fork, or pendulum linkage (the name is usually shortened to “wishbone suspension”). This type of suspension soon became ubiquitous, which we still see today, although compared to the original design, as a result of its development, the use of modern materials, and improvements in the shock absorbers used, many variants of this suspension have appeared.

One of the main requirements for the rear suspension of any design is the ability to ensure that the wheels are in the same plane, and the wheel axle at right angles to the centerline of the steering column. This depends on the strength and stiffness of the suspension, as well as the ability of the joints to withstand high axial and radial loads.


The frame is designed to perform a number of functions, which can be divided into “structural” and “geometric” functions.

From a structural point of view, the frame serves to locate and mount the engine, transmission. suspension and other auxiliary parts. In order to effectively perform this function, the frame must be rigid, strong and as light as possible.

Geometrically, the frame provides the required steering and suspension geometry, wheelbase and center of gravity. In addition, the frame has another important function: it ensures that the wheels are aligned. The frame must be rigid enough to withstand the forces of cornering, acceleration and braking without steering and suspension action. In this case, the main criteria is the mutual positioning of the steering column and the suspension arm swing axis – the frame must ensure that the steering column is maintained in the vertical plane and the suspension arm swing axis in the horizontal plane that is perpendicular to it.

These are the factors that have defined frame design since the first motorcycles. If the frame is not of adequate strength and stiffness, front wheel-to-rear wheel misalignment can occur, ranging from slight to downright dangerous. Lack of frame stiffness can not only make the machine difficult or uncomfortable to ride, it can also negate the advantages of the engine, forcing a cautious riding style, leaving this model far behind its “stiffer” rivals. Over the years, many examples have accumulated in the field of racing motorcycles, when machines with excellent frames, but modest engines defeated competitors with great engines and questionable chassis.

The road motorcycle market sets different requirements that guide the final choice of frame type for a particular model. In this regard, cost and shape are almost as important as other frame characteristics. It is undeniable that a well-designed frame can transform almost any machine. The attention to detail that only comes with low-volume production (which results in high costs) explains the enduring popularity of tuning frames. In the rather highly specialized areas filled by manufacturers of racing motorcycle frames and road tuning frames, such as Bimota and Harris, a combination of intuition, knowledge and craftsmanship is evident.

Electrical equipment

Electrical equipment is present to some degree on any motorcycle, moped or scooter. In most cases, the electrical equipment is powered by a battery that serves the needs of the machine’s lighting, signaling and monitoring systems. Many people have a hard time getting acquainted with electrical equipment, and some give up trying to learn it too early due to a lack of knowledge in physics. But a logical application of a few basic rules will make it easier to understand the system and troubleshoot it.

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