Home / Two-wheeler Insurance / Articles / Explained: V-Twin, Stroke, and Valve in Bikes
Team AckoApr 12, 2023
Biking terminology can be tricky to understand and remember. We’ve all been there – trying to keep up with conversations where words like “Stroke” and “Valve” are frequently used. Technology, while based on simple concepts and science, requires a little context and detangling, when sitting down to understand what’s happening inside an engine. Life is simpler when you know how various components of your bike come together and interact with each other.
Let’s now deconstruct common biking terminology to make it simpler to follow. When you are through reading this blog, you will have understood these three aspects of a motorbike:
V-Twin is actually the engine of your bike. It is also called the “V2” engine. The number signifies the number of cylinders in the engine – the V-Twin, thus, has two cylinders with pistons. The interesting thing about this engine is that these cylinders are arranged in a “V” shape, hence the name.
V-Twin engines are commonly found on motorbikes, although they can also appear in smaller cars or industrial equipment. The angle between the two cylinders that form the “V” is kept at 90 degrees for most arrangements because this angle provides good stability and primary balance, when used in conjunction with a correct counterweight. However, because of the 90-degree angle between the arms, these engines may sometimes be referred to as “L-Twin” instead of “V-Twins”. For the V-Twin engines with acute angles (less than 90 degrees), the balance is achieved using crankpins.
One of the most popular examples of V-Twin bikes in India is the Suzuki V-Strom 650 XT.
There are two ways in which a V-Twin engine can be arranged on a bike:
To understand this arrangement, you have to imagine a 2D diagram of your bike. Between the two wheels, your engine would be mounted on the same plane with its cylinders and crankshaft visible, forming a “V”.
The second way to mount an engine on 2-stroke bikes in India is to house it on a plane perpendicular to the plane of your 2D bike. This arrangement is less common. However, it is considered better for engine cooling as both cylinders receive access to the air stream.
V-Twin engines on a bike work the same way as any other vehicular engine. The process is explained in the steps below:
The fuel intake is activated, and a mixture of fuel and air is pumped into the engine through a carburettor, where it is ignited by a spark.
The fuel and air mix then explodes, and pushes the pistons forward into the cylinder shafts – the process is continuous, and the pistons keep moving up and down until they receive these fuel-air explosions.
The movement of the pistons turns the crankshaft attached to the V-Twin assembly, converting the heat energy of the fuel into the rotational energy of the crankshaft.
The transmission rails then relay this rotational energy to the rear wheel of your bike to get it to move.
To understand what stroke means in biking language, you must first know what a combustion cycle is.
The combustion cycle of a V-Twin happens in four stages:
During this combustion cycle, the activities happening between the fuel combustion and gas expulsion stages define the stroke of your engine. Between the intake and expulsion stages, the pistons of your 2-stroke bike are moving up and down – propelled by the combustion of a fuel-air mixture. The stroke, thus, can be defined as the motion that a piston goes through in the cylinders of your engine. An associated term with stroke is the “Length of stroke”. Evidently, this is the distance that the pistons travel during their stroke. Typically, it is a couple of inches long.
V-twin engines come in two configurations:
Here, 2 and 4 signify the number of times the pistons must move to turn the crankshaft in one full rotation. Let’s understand in full detail.
A 2-stroke movement essentially means that the engine takes two full movements of the pistons to turn the crankshaft in one full rotation. In these two strokes, the engine must achieve all the stages of a combustion cycle – intake, compression, combustion and exhaust.
Since a 2-stroke engine gets only two piston movements, the stages of the combustions cycle are combined and distributed among these strokes:
In one stroke, the engine combines fuel intake and exhaust
In the second stroke, the engine combines compression and combustion
A 4-stroke movement essentially means that the pistons take four movements to turn the crankshaft in one complete rotation.
Each stage of the combustion cycle in a 4-stroke engine gets one full stroke:
One stroke takes fuel intake
Second stroke achieves compression
Third stroke achieves combustion
Fourth stroke expels gases
Let’s discuss this section separately for 2-stroke and 4-stroke V-Twin engines.
As the name implies, a 2-stroke engine completes the combustion cycle in 2 movements of the piston.
It is called the down stroke because the piston is traversing downwards. The downstroke involves inletting fuel into the chamber through the inlet valve while expelling exhaust through the outlet on the side.
Therefore, two actions happen in parallel in one stroke – intake and exhaust.
It is called the upstroke because the piston is now travelling upwards. As the piston moves upwards, it compresses the air-fuel mixture that came in through the inlet in the previous stroke. When the desired compression is achieved, a spark ignites this air-fuel mixture and pushes the piston back into the downstroke. Therefore, two actions are happening with the same stroke: compression and combustion.
As opposed to a 2-stroke, a 4-stroke engine requires four movements of the piston to complete one full revolution of the crankshaft.
Stroke 1 – in this stroke, the intake valve opens up, and the piston moves downwards, letting the air-fuel mixture enter the engine.
Stroke 2 – in this stroke, all the valves are shut as the piston moves upwards and compresses the air-fuel mixture.
Stroke 3 – as the valves remain closed and the piston is in compression position, a spark ignites the compressed fuel mix, and combustion happens.
Stroke 4 – all valves remain closed as the exhaust valve opens up. The piston moves forward and expulses gases.
Valves in a V-twin engine perform the same function as any other valve in the physical world. Their primary function is to keep the fuel and energy where it is supposed to be in an engine. They perform the function of an inlet and outlet according to the position of a piston in the combustion cycle.
In a 2-stroke engine, there aren’t any “valves” per se – these engines have “ports”. There are three ports in a 2-stroke engine:
Inlet port for inducting air-fuel mixture
Outlet port to let exhaust gases out
Transfer port to transfer the charge from the crankcase to the head
On the other hand, a four-stroke engine can have two or four valves. When there are two valves, one is used for intake and one for exhaust. When there are four valves, two are used for intake and two for exhaust.
The concept of V-twin engines is quite simple to understand because these are one of the classic types of engines still in use. Now you know what a V-Twin engine is, what strokes it works on, and how many valves it needs to run properly. For a more in-depth understanding of v-twin bikes in India and 2-stroke bikes in India, you can visit Acko.
No, V-twin engines are not obsolete yet. In fact, because of the good horsepower, they can create with a cc rating of lower than 1,000. Some superbikes today, like the Ducati 851/888, use V-twin engines.
A V-twin engine can either have 2 strokes or 4 strokes. However, you have more types of engines where the number of cylinders is more, giving you more power and speed.
Bigger bore engines give you more power with each stroke. This is because valve openings are bigger, which draws in more fuel per stroke. If you want more power for the same engine size, go for a bigger bore.
The stroke length of an engine determines the fuel efficiency and power it can deliver to your vehicle. Vehicles with shorter stroke lengths operate at higher rotations per minute.
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