Different Types Of Motorcycle Engines
Modified On Apr 29, 2019 11:55 AM By Gaurav Sadanand
Confused about the different layouts of motorcycle engines? We’re here to help
Until about a decade ago, a majority of the motorcycles in India were limited to single-cylinder engines thanks to ours being a price-sensitive market. However, as the years passed and the two-wheeler industry grew, big manufacturers like Kawasaki, Triumph, BMW and Suzuki started entering the market with performance-oriented motorcycles sporting multiple cylinders. These range from parallel twins to massive flat-six engines. But their layouts, advantages and disadvantages can be a bit confusing, so let’s take a closer look at each type of engine to help you understand it better.
A single-cylinder architecture is most commonly used on commuter motorcycles because it’s cheap to produce and easy to fix and maintain. A lonely piston does all the hard work here, but being an inherently unbalanced system, it’s prone to a lot of vibration, especially in the case of larger cubic capacities. So it’s optimal for small displacement motors (i.e. 100-200cc), as it keeps the reciprocating mass (piston) low, and is seen regularly on budget-friendly motorcycles like the Bajaj Discover 125, Honda CB Hornet 160R or the Suzuki Gixxer. That said, single-cylinder engines can also be found on performance motorcycles, such as motocross bikes or rally bikes, or even the world’s most powerful single-cylinder bike, the KTM 690 Duke. The engine block can be mounted sloping forward, at a 90-degree angle or in rare cases, even sloping backwards (as on the BMW G 310 series).
Parallel twin engines or an inline-two engine have an extra cylinder at their disposal. The main distinction of parallel twin engines is that they have these two cylinders placed parallel to each other and they share one cylinder block (unlike V-twins which require two separate cylinder blocks). This type of engine construction is often seen on entry-level sportbikes such as the Yamaha R3 or Kawasaki Ninja 300, but is in use even on large-capacity cruisers like the Triumph Thunderbird or even on mid-capacity adventure bikes such as the BMW F 850 GS. This layout is preferred for its compact dimensions and ease of construction (as compared to a V-twin). It’s generally a more balanced system compared to a single cylinder as the movement of one piston cancels out the movement of the other (depending on the firing order, of course - but we’ll get into that later). So they offer smoother power delivery compared to V-twins.
An inline-three mill uses three parallel pistons housed within the same cylinder block. The main advantage of this type of configuration is that it offers somewhat of a middle ground between a V-twin and an inline-four engine. It’s a lot smoother compared to a V-twin and is narrower than an inline-four, making it easier to shoe into the compact dimensions of a sportbike. This configuration does have the tendency to rock end-to-end slightly as cylinders one and three are near the opposite ends of their strokes. Also, unlike an inline-four mill, the vibes cannot be cancelled out thanks to the odd number of cylinders. The Triumph Street Triple and the MV Agusta Brutale 800 are two such examples.
When you have four parallel cylinders packaged in a single cylinder block, you get an inline-four engine. With an even number of pistons, the movement of the pistons can be balanced out really well, making them one of the smoothest running engines on a bike. This smoothness allows them to be revved very high without risking damage to engine components through vibrations, and hence these have some of the best power-to-weight characteristics of any motorcycle engine configuration, although that does make power delivery quite peaky. No wonder then that this is the go-to configuration for almost all 600-1000cc sportbikes. The Benelli 600i, Kawasaki Z900 and the Honda CBR1000RR are some examples.
The horizontal or “flat” layout of the engine is commonly known as a boxer engine. Here, the two pistons are laid out on opposite sides of the crankshaft. A flat-twin’s firing order is the same as a 360-degree parallel twin; however, in this case, the pistons are moving away from each other rather than in sync. The complicated setup is expensive to manufacture, maintain and fix. Also, since their crankshaft is in the motorcycle’s longitudinal axis, these bikes are known to have a ‘torque reaction’, where the bike is pushed in the opposite direction of the crank’s rotation when the throttle is opened. But the advantages of this layout are that it keeps the bike’s centre of gravity low and allows for better air-cooling of the cylinders as they are exposed to more air on each side of the bike when in motion. The BMW R nineT and GS use boxer engines.
Flat-four & Flat-six:
A flat-four or a flat six engine has a similar internal construction as a boxer engine, albeit with extra cylinders. These engines are a lot smoother than inline-three or inline-four engines and maintain the perfect power delivery rate. Honda introduced the 1000cc flat-four engine with the Gold Wing back in 1975. It currently runs on a bigger 1,833cc flat-six motor.
As the name suggests, the arrangement of the two-cylinders forms a “V” here. Bikemakers have tried various angles between the cylinder heads and each has their own preferred configuration. Harley-Davidson, for example, runs with a 45-degree V angle on nearly all their motors as it gives them loads of bottom-end torque and that distinct ‘potato-potato’ exhaust note.
On the other hand, Ducatis use a 90-degree V angle on their angled V-twin motors (when one cylinder is nearly horizontal and the other is nearly vertical - also called an L-twin). While most V-twins are mounted with transverse crank layout (where the crankshaft runs perpendicular to the bike’s longitudinal axis), some manufacturers such as Moto Guzzi have chosen to go with a longitudinal crank layout (where the crank is laid out along the bike’s longitudinal axis). V-twin engines have an uneven firing order which gives them the angry "burbling" exhaust note and are known to produce a ton of torque at low revs, but are also known to have a fair amount of vibrations and require balancer shafts to cancel them out.
A V4 engine is basically two V-twins stuck together. It has some of the smoothness of an inline-four mill and the raw bottom-end torque delivery of a V-twin. All this while sounding like a raging bull. It’s also more compact than a transverse inline-four, which makes for a snug fit inside the motorcycle frame. Although, having two sets of cylinders at opposite ends means manufacturing two intake and exhaust systems, cylinder heads etc. which makes a V4 engine more expensive to produce than an inline-four motor. The 2019 Aprilia RSV4 1100 Factory or the Ducati Panigale V4 should ring a bell.