Motorcycle Engines Explained

Motorcycle Engines Explained

by Chris Rutter January 07, 2021

Motorcycle engines come with a variety of configurations, final drive systems, cooling systems and much more. If you're curious about the differences between all these options, you've come to the right place. We've put together an easy-to-understand guide on the different types of motorcycle engines as well as their effect on bike performance, cost and other factors. 

Engine Configurations

There is a large number of motorcycle engine configurations out there, and it's often difficult for beginners to tell the difference between them. Below is a brief explanation of each configuration, starting with the most common ones. 

Common Configurations

Single-cylinder motors are commonly found in a number of entry-level sports bikes.

Single-cylinder motors are the simplest engine configuration and are commonly found in dual-sports, dirt bikes, scooters and a number of entry-level sport bikes. With fewer components than other engine configurations, singles are relatively inexpensive to manufacture and maintenance is minimal. However, single-cylinder motors do produce lots of vibrations, which is why they're generally only made in smaller sizes. 

Other common motorcycle engine configurations include:

  • Parallel-twins: The parallel-twins engine configuration features two adjacent cylinders located over the crankshaft and provides a responsive riding experience. Like single-cylinder motors, parallel-twins also produce lots of vibrations, but their simplicity and efficiency have made them common in commuter and standard models.
  • V-twins: V-twins are the most common configuration in North American bikes, and many love them for the great low-end power they provide. As suggested by the name, this configuration features two adjacent cylinders that make a V shape. Another characteristic of V-twins is the position of their intake, which is usually between the cylinders. Like with most other inline engines, the intakes are located behind the cylinders. 
  • L-twins and transverse V-twins: Named "L-twins" due to its L-like shape, this engine configuration is found in almost all Ducati's motorcycles. It's also found in Moto Guzzi motorcycles — although in Guzzi bikes, the engine is mounted from side to side rather than mounted front to back.
  • Flat-twins: Flat-twins are twin-cylinder engines that have their cylinders horizontally positioned, or flat. The pistons are found on opposite sides of the crank. Flat-twins are exceptionally well balanced and produce lots of power throughout their whole rev-range. They also provide a low center of gravity, although their lean angle is limited due to their width. This limitation is not generally an issue on the street. Flat-twins are also sometimes called "boxer twins." 
  • Inline-threes: Inline-threes are similar to a parallel-twin but with an additional cylinder. They do not have a lot of high-end power or extremely high top speeds, but they provide exceptional amounts of torque at low and medium rpm. This makes them great on the road. 
  • Inline-fours: Inline-four engines provide an impressive amount of power and are characterized by their adjacent cylinders. They provide the fastest-revving and smoothest engines currently available and power most supersport and superbikes. The four-cylinder rockets produce an astonishing amount of power, particularly at higher rpm. Despite being the fastest bikes in existence, on the street, they're very impractical. 
  • V-4s: Perhaps best described as two V-twins joined together, V-4s have two cylinders at each end of the V. Like inline-fours, V-4s provide enormous amounts of power and are found on many MotoGP bikes by Honda, Ducati and other factory race teams. Due to their high manufacturing costs, V-4s are generally found on pricier models like Aprilla's RSV4 or Panigale V4. V-4s also tend to weigh more than inline-fours. 

Rare Configurations 

Although you're less likely to come across the following configurations in motorcycles, you may be interested in learning about them. They include: 

  • Flat-fours and flat-sixes: These models, which are like flat-twins with more cylinders, are not common and are hardly seen except for on big touring models. The Gold Wing by Honda, which features three cylinders that are horizontally laid out on either side of the engine, is an example of a modern flat-six.
  • Inline-sixes: The inline-six is like the inline-three or inline-four, but it has six cylinders. These six cylinders are positioned next to one another. 
  • V-8s: Commonly used in cars, SUVs and trucks, the V-8 can be thought of like a V-4 or V-twin, but with eight cylinders total. Due to their enormous size and width, V-8s are rarely found in motorcycles, although there are several modern examples. These include the PGM V-8, the Lazareth LM847 and the Boss Hoss cruiser. 
  • Square-fours: The square-four engine, which is like a connected set of parallel-twins, first became famous when it was featured in the 500cc Ariel Square Four. Although these engines did not have exceptional raw power, they compensated for it with their smooth delivery. Square-fours are thought to be a bit old-fashioned but historically significant. 
  • Oval-piston V-4: When the Oval-piston V-4 was first introduced in 1979, it was meant to provide the same benefits as a V-8 with only four cylinders. This was the cylinder limit for bikes competing in Grand Prix motorcycle racing. This was achieved by basically designing a V-4 that featured two connecting rods that are joined to each piston. It also featured eight valves and two spark plugs. 
  • V-5: A V-5 is essentially a V-4 with an additional cylinder. Although well balanced and powerful, V-5s also cost a lot to make and maintain, which means bike manufacturers infrequently use these engines. 

Cooling Method 

Motorcycle engines can also be categorized in terms of how they are cooled, which is either by air or liquid:

  • Air-cooled: Air-cooled bikes are cooled by air that passes around and over the power plant. To get the most out of this effect, "cooling fins" are sometimes used, which allow a greater amount of surface area to be exposed to the air. This more efficiently dissipates heat, keeping the engine from overheating. 
  • Liquid-cooled: Liquid-cooled engines are cooled by a liquid, with some models also sporting cooling fins. If you see a radiator on a motorcycle, it means the bike is probably liquid-cooled. 

Final Drive Systems 

 The final drive of a motorcycle describes how power is transferred to the back wheel.

The final drive of a motorcycle describes how power is transferred to the back wheel, and there are three primary ways it is achieved: 

  • Chain-driven: The most popular final drive found on motorcycles is a chain drive that consists of two sprockets with the front one attached to the engine and the back attached to the rear wheel. In other words, the setup is like a bicycle. Chain drives offer many advantages — they're the cheapest option of the three, they allow for many gearing options and they can be easily replaced. 
  • Belt-driven: A belt-drive system utilizes grooved rubber belts that are reinforced with metal wiring. They require no lubrication, are long-lasting and are quieter than chain drives. 
  • Shaft-driven: A shaft-driven bike uses a spinning, enclosed shaft. This shaft turns a cog that is attached to the back rim, and this back rim powers the motorcycle. This setup is similar to what most cars use. Because this system is enclosed, it is not exposed to water, dirt or any other type of grime the bike might encounter on the road. 

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Chris Rutter
Chris Rutter

Author




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