The Pros and Cons of Every Motorcycle Engine Type

The most significant and valued part of a motorcycle is its engine and in the motorcycling world, an engine is termed the heart of a motorcycle. It keeps the motorcycle running and functional by performing the most essential tasks. The engine performs the most vigorous tasks and takes the most wear and tear throughout combustion, exhaust, power generation, and power delivery to the rear wheel. A motorcycle's price, value, and performance are majorly decided and judged by the engine's size, characteristics, layout, and the quality of its output. The motorcycle engine technology has seen tremendous upgrades and transformations since its birth. Starting from the very basic clip-on engines that were installed on the cycles, known as mopeds (motorized bicycles) to the point where motorcycles are equipped with 2,500 cc engines that are often controlled with electronic computer chips. The research & development sectors of every motorcycle manufacturer have contributed a lot. If you are not familiar with the type of motorcycle engines, their technology, their purpose, their merits, and their demerits, read this article to learn about the pros and cons of every motorcycle engine type used in motorcycles.

To start with, we will choose the most basic type of engine with only one cylinder, called the single-cylinder engine. It is the simplest type of engine with a basic construction and design. Being fitted with only one cylinder, a single-cylinder engine has several benefits mentioned later in this article.

Single-cylinder engines are also known as thumps because of the sound they produce. If you observe the power cycle of a single-cylinder engine, it stays quiet for most of the time during the intake, compression, combustion, and exhaust phases, delivering the power to the rear wheel in a pulse. As a result, the engine produces a thumping sound.

Single-cylinder engines do not produce a continuous power output. A single-cylinder engine produces power in a pulsating form, permitting the rear wheel to apply traction and ensure better control of the dirt bike whilst maneuvering on challenging terrains. If continuous engine power is delivered to the rear wheel of a dirt bike, it will not allow the motorbike to stabilize itself and get used to bumps and changes in terrain.

To increase the engine displacement, another cylinder was added to a single-cylinder engine to make a twin-cylinder motor positioned in a V-shape. These engines are mostly installed on cruisers and touring bikes. Harley Davidson is one of the giant and oldest motorcycle manufacturers that has been using the V-Twin engines in its motorcycles for more than a century. The company has played a major role in making V-Twin engines one of the most popular power plants installed in motorcycles, especially among American riders with its Milwaukee-Eight V-Twin engines.

Despite the addition of a separate cylinder, the weight does not increase drastically as the engine uses the same crankshaft and crankpin.

The initial V-Twin engines were not as heavy and the angle between the two cylinders was not as big as it is now in the modern V-Twin. It is due to the fact the early V-Twin engines had small bores and cylinders. However, with the increase in the displacement, cylinders, and bores of an engine over time, the angle between the two cylinders in a V-Twin also needed to be increased to prevent pistons from getting into contact at the bottom end.

• The L-Twin engine is one of the most notable inventions in the motorcycling world by Ducati in 1970. It has become the trademark and the most iconic engine used in Ducati motorcycles.
• The two cylinders have an angle of 90° between them. This is because the engines continued getting bigger and the angle between the two cylinders in a V-Twin continued to increase.

Another variation of a twin-cylinder engine is the inline twin-cylinder engine, famously known as the parallel-twin engine. A parallel-twin engine is one of the most widely used engines in motorcycles due to the several benefits it provides. To reduce the weight and additional parts in a V-Twin engine, inline twin-cylinder engines were introduced, which turned out to be a useful experiment.

In an inline twin-cylinder engine, the cylinders and pistons are positioned side by side, which helps to use a common crankshaft, valvetrain, and cylinder head. The crankshaft is longer and separate crankpins are used in an inline twin-cylinder engine as the pistons and cylinders are placed parallel to each other, and they do not meet at a common point.  

To overcome the parallel-twin engine rocking couple issue, a new configuration was introduced by Max Fritz, a core engineer working at BMW. This new configuration involved the positioning of twin cylinders in a horizontally opposed fashion. The engine became famously known as the boxer-twin engine by BMW, also known as the flat-twin engine. It instantly became a hit among motorcycle enthusiasts and is even used in several modern BMW motorcycles.

In a boxer-twin engine, the cylinders are placed at 180° from each other. Such a configuration makes the motorcycle wider from both sides.

Flat four-cylinder engines are most commonly used in heavyweight vehicles due to their design and size. When it comes to powering the motorcycles, flat-four engines were only installed on a few models, like the 1974 Honda Gold Wing.

A flat-four (Boxer-Four) engine has four cylinders, two on one side and two on the other side, facing each other horizontally.

A flat-six (Boxer-Six) engine is an extension of a flat-four engine with two more cylinders and pistons. These engines are still being used on the modern Honda Gold Wing. The 2014 Honda Valkyrie was also fitted with a flat-six engine.

Inline three-cylinder engines are an extension of an inline two-cylinder engine with an extra cylinder and piston attached to the crankshaft. Thanks to their layout, these engines can rev faster than twin or single-cylinder engines. With three pistons moving around the same crankshaft, there is not even a single instance during the cycle when all the pistons stop at once. At least one piston in an inline three-cylinder engine is always moving, ensuring more horsepower and higher rpms.

In single and dual-cylinder engines, there comes a moment during the stroke cycle when the pistons become stationary. These points can either be at the top or bottom while the piston is moving, resulting in a shorter power stroke. Meanwhile, an inline three-cylinder engine eliminates this issue and ensures better speed and acceleration.

Apart from all the good characteristics, three cylinders are incapable of creating a balance in the motion, resulting in harsh vibrations. The cylinders of these engines can only be balanced along the axis. If you balance the forces acting on the horizontal axis, they will create an imbalance in the forces acting on the vertical axis.

To resolve the balance issue that surfaced in an inline three-cylinder engine, a four-cylinder engine was designed. It has the same layout as the inline twin-cylinder and the inline three-cylinder engine, with the addition of the fourth piston attached to the crankshaft. As the number of pistons is even, it helps create a balance in the movements of pistons around the crankshaft and offers smooth power delivery.

Inline four-cylinder engines are properly balanced as they cancel out vibrations and rocking couple, ensuring an uninterrupted fast movement of the crankshaft. This, in turn, makes the motorcycle move at a high speed, thanks to the impressive horsepower produced by inline-four engines.

With four pistons attached to the crankshaft in inline four-cylinder engines, there is not a single instance when the crankshaft is not provided with a force to continue rotating. Meanwhile, in a single or twin-cylinder engine, the crankshaft completes the revolution with the help of the moment of inertia, which is why these engines make thumping and potato sounds.

When you turn on a motorcycle powered by an inline-four engine, it does not produce a thumping sound or a famous V-twin sound due to the presence of the power strokes throughout the four-stroke cycles. In every instance, at least one piston in an inline-four engine is in the combustion phase, resulting in a louder sound, which is why these engines are commonly known as screamers.

Like the inline-twin (parallel-twin) engines have a rocking couple issue, the inline four-cylinder engines have the worst secondary imbalance problem. Despite having perfectly balanced pistons, cranking at regular intervals, the secondary imbalance occurs due to the difference in the velocities with which the pistons move in a revolution.

To overcome the secondary imbalance issue, a mid-stroke is required to move pistons with uniform velocities throughout the revolution. The issue was resolved by introducing counterbalancer shafts that overcame the secondary imbalance issue to a certain extent. Counterbalancers are additional weights installed on the pistons that cancel out the imbalance forces produced when the engine works.

A further extension to an inline four-cylinder engine is the inline six-cylinder engine, with two more additional pistons attached to a further extended crankshaft. Installing six pistons on a single shaft makes these engines too large and heavy for conventional motorcycles.

Apart from being large and heavy, inline six-cylinder engines proved to be ideal when it comes to nullifying all the imbalance forces responsible for rocking couple, secondary imbalance, and other vibrations.

The V4 engines power most MotoGP motorcycles. However, it takes engineering excellence and a lot of money to manufacture V4 engines. This makes the V4 engine-powered motorcycles extremely expensive.

The V4 engines feature one of the trendy and present-day engine designs with 4 pistons positioned in a V-form configuration connected to a common crankshaft. The V4 configuration allows the engineers to use a smaller crankshaft, which may not eliminate the imbalance forces but reduces the vibrations greatly, ensuring smooth-riding operation.

Rather than growing the engine's dimensions, a V4 design makes use of a huge bore design, which improves the performance in terms of getting extra horsepower, higher rpms, and high speeds.

Motorcycles are generally characterized by their engine type, displacement, and layout. This is because a motorcycle’s performance majorly depends on its engine. Every motorcycle engine has unique characteristics and is designed for a specific purpose. Not every motorcycle engine can be perfect, highly versatile, and suitable for all riding conditions. For example, a single-cylinder engine is the most lightweight and cheap option, making it ideal for dirt bikes. V-twin engines are ideal for cruisers and touring bikes as they ensure an ideal balance of horsepower and torque for heavyweight motorcycles. Boxer engines solved a major rocking couple issue and reduced vibrations significantly. However, new issues like the reduced ground clearance and decreased leaning angle surfaced. In an attempt to produce more powerful engines, the inline-three was produced, which ensured better horsepower and higher rpms. However, the installation of three cylinders in an engine created an imbalance, which was later improved in the inline-four engine. Although the inline-four successfully removed primary vibrations and rocking couple, it gave birth to secondary vibrations, which were eliminated by the inline-six engine. However, installing six cylinders made the engine and the motorcycle extremely heavy. So far, the most balanced, powerful, and ideally-designed engine is the V4. Apart from several advantages of a V4 engine, it is one of the most expensive engines mostly used in high-speed, performance-oriented motorcycles.

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