If You Don’t Understand the Bike Jargon…
Definition of each term can be written as a big book but here I am trying to mention more terms restricting to the basics. These definitions of the terms used in the motorcycle specifications are intended to help you to learn more about your bikes. The more you understand about your bike there is likelihood that you can help it perform its best!
No. of Strokes: My site is discussing only about the four-stroke motorcycle engines, although, there are two-stroke engines too. So I urge you to never get confused a four-stroke with four-cylinder or two-stroke with two-cylinder because these are totally 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 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.
Cooling: By running a coolant through the engine the heat generated in the engine can be exchanged through the radiator just like in a car to make the engine liquid-cooled. However, through airflow just above the fins on the engines these can be air-cooled too. The circulation of engine oil will take place in the engine and the exchange of heat will take place through a small radiator for what is called as oil cooling.
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.
Number of Cylinders: There will be as many as 1 to 6 cylinders in the engines. Small bikes use a single-cylinder engine that is also called as a thumper. 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 each other.
- 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.
- 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 Honda ST1300.
- 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.
Displacement: The volume displaced as the pistons move from their bottom position to their highest position in 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 we see only the cc displacement bikes.
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, carburetor(s) or fuel injection is 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 carburetor name and the number of carburetors 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 depending on their engine, for the fuel injection.
Compression Ratio: Compression Ratio could be explained like this: Take some 100cc 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 what value of engine revolutions per minute (RPM). It can be simply explained as the twisting force. Torque is that quality of the engine that is expressed when you use the throttle aggressively and accelerate hard. It is just the feeling and needless to say will be felt as more forceful when the number is high.
Maximum Horsepower: Maximum amount of horsepower delivered by the engine occurs at a particular engine speed. It can be derived through the formula : Horsepower = Torque × RPM/5252 .So said, both the horsepower as well as torque are interrelated.
Watch for more gyan that follows on the technical jargon of your bikes in the coming days! Keep visiting the site! If you have any doubts do not hesitate to ask me, I will be pleased to learn and let you know!