What is bore? What do they mean by V-twin? If you are unaware of the very basic bike terminology, this article will help you understand the fundamentals the next time you read any motorcycle’s spec sheet…

You often come across terms which are almost used everytime someone describes a motorcycle, which you do not understand. Terms in a motorcycle’s specification that is listed on company’s pages, websites, may seem a little complex for a person who is not well versed with motorcycles, or engines, in general! In this article I am posting about the very basic understanding of bike stuff. Time to learn!

Definition of some of these terms can be as exhaustive as a thick book but as the heading infers, here I am trying to only give you the very basic understanding. These definitions of the terms used in the motorcycle specifications are intended to help you to learn more about bikes in general. The more you understand about your bike there is a likelihood that you will treat it better.

Bike Jargon Explained

No. of Strokes: Do note that we are discussing only four-stroke motorcycle engines and not two-stroke motors. I also urge you not to get confused between four-strokes and four-cylinders or two-strokes with two-cylinders because they are completely different from each other.

The definition of the four strokes in a four-stroke engine is as follows:

  • Stroke 1– Intake valve(s) open, piston moves down and the air/fuel mixture is sucked inside
  • Stroke 2– All of the valves are closed, piston moves up squeezing the mixture.
  • Stroke 3– All of the valves are closed and a spark plug ignites the fuel/air mixture, pushing the piston down.
  • Stroke 4– All but the exhaust valve(s) are open, piston moves up, blowing the old charge out of the exhaust valves.

A short version is Suck, Squeeze, Bang and Blow.

Cooling: By running a coolant through the engine the heat generated can be exchanged through the radiator just like in a car (for liquid-cooling). Air For air-cooling, regular air flows on the fins of the engine to cool it down. Another method of engine cooling is oil-cooling wherein the circulation of engine oil takes place in a small jacket ahead of the engine. In this process the engine oil is cooled by air and this cooled engine oil is what gets circulated inside the engine.

Air Cooled vs Oil Cooled vs Liquid Cooled Engines – Explained in Simple Terms

Valves: The use of the valves is as mentioned above. For the purpose of intake and exhaust; however, there maybe use of one or more valves. The number of valves used per cylinder or for the whole engine maybe indicated by bike manufacturers. As the indication of closed and opened valves, terms such as SOHC (Single OverHead Cam) or a DOHC (Double OverHead Cam) etc., are also used. To operate the valves, there are other methods as well.

Bike Jargon

Number of Cylinders: There will be as many as 1 to 6 cylinders in the engines. Small bikes which we get in India traditionally use a single-cylinder engine. Engines with two-cylinders arranged in several configurations can be seen in many bikes that include:

  • V-twin – Here the cylinders are spaced at a particular angle looking like a V to the onlooker.
  • Parallel twin – In this, the two cylinders are right next to each other in a vertical position.
  • Flat-twins – Here the two cylinders are opposed as seen in the BMW Boxers.

There are many engines that come with more than two cylinders. They include:

  • Triples – three cylinders are lined up next to each other in a vertical position, say the parallel triples.
  • In-line fours – this is similar to a triple except with another cylinder added to it.
  • V-4 engines – four cylinders and placed as V, like the one used in Ducati Panigale V4.
  • V-6 engines – six cylinders as V, like the ones used in Boss Hoss.
  • Flat-6 engines – six cylinders like the one used in Honda Gold Wing 1500/1800s.

There are other engines as well but right now let us keep it limited to these only.

Displacement:
The volume displaced as the pistons move from their bottom position to their highest position inside the cylinders of an engine is called as displacement. Measurement of displacement is either in cubic centimeters (CC) or cubic inches (CI), although, in India cc is the more frequently used term.

Bore and Stroke: Diameter of the cylinder in the engine in which a piston moves up and down is bore and the distance which the piston moves up and down in the cylinders is known as stroke.

Fuel System:
To control the mixture of air and fuel, carburettors or fuel injectors are used. During Stroke 1, the mixture of air and fuel get prepared to be sucked through the intake valves and in through the cylinders. The carburettor name and the number of carburettors used are usually identified by the specifications. Fuel injection (FI), Digital Fuel Injection (DFI), Programmed Fuel Injection (PGM-FI), Electronic Sequential Port Fuel Injection (ESPFI) etc are the different names used by different bike manufacturers for the same tech of fuel injection.

Compression Ratio: Compression Ratio could be explained like this: Take some 100 cc water and pour it through the sparkplug hole when the valves are closed and also when the piston lies at the cylinder bottom. Then, it is like full. And, you can at the most pour only 10cc of water in to the hole to fill it, when the piston comes at the top of its stroke, then the ratio for compression is 100 to 10 or simply 10 to 1. Engines make more power when there is a higher compression ratio also implying that they require more fuel.

Maximum Torque: Torque is the maximum amount of twisting force given by the engine and at certain value of engine revolutions per minute (RPM). It can be simply explained as the pulling power of an engine. The lower the engine rpm, the easier it is for a motorcycle to push load. As a very basic example, Royal Enfield’s, owing to their higher torque are good at ‘pulling’.

Maximum Horsepower: It is simply the power produced by an engine and occurs at a particular engine speed. It can be derived through the formula : Horsepower = Torque × RPM/5252. This also tells us that both the horsepower as well as torque are interrelated.

As we said, this is just the very basic definition of these terms. You can head to our ‘Informative’ section to read more such stories…