Ah! Another blog post on 2-strokes! Hans, you need help, my friend, otherwise, you will go crazy! Yeah, that’s what you are thinking when I write another blog post based on 2-strokes. But, hear me out! This one is worth your time and might enlighten you on what makes 2-strokes special and why they are not mainstream.
Now, keeping aside my fanatic blabbering about the legendary RD350 and the legendary RX100, let’s get to the basics. What is a two-stroke engine, and how does it work differently from a 4-stroke? 2-stroke, as the name suggests, is an internal combustion engine that goes only through 2 cycles, or 2 strokes, unlike the very commonly used 4-stroke engine, which goes through 4 strokes or 4 cycles. To be precise, a 4-stroke engine, the generally used type of engine, goes through 4 strokes-intake, compression, power, and exhaust. Whereas, 2-strokes work differently. They only go through 2 strokes of the combustion cycle to complete the combustion or power stroke, and the exhaust stroke. The advantage of a 2-stroke is that a 2-stroke has simpler mechanics, is lighter, and is cheaper to manufacture, and, it produces power in just 2-strokes instead of four, technically, making it more efficient. Also, it has a better power-to-weight ratio, making the whole vehicle lighter. The piston of a 2-stroke engine is doing quite a lot of work. It is drawing air and fuel into the crankcase while it’s pressurizing the air and fuel on the chamber and it is forcing up air and fuel to the chamber when it is being driven down by combustion. On one side is the combustion chamber, where the pistons compress the air-fuel mixture and capture energy released by the ignition of the fuel on the other side of the piston is the crankcase. The crankcase also acts as an air chamber or reservoir as the piston drives up on its combustion stroke. It’s creating a vacuum to suck in air and fuel from the carburetor through the reed valve. The valve doesn’t need to be mechanically actuated because of the airflow. Once the combustion stroke starts, that pressurizes the crankcase, the valve closes in the air, and fuel is forced into the combustion chamber, meanwhile, it’s the sides of the piston that are doing the job of the valves in a 2-stroke engine, by covering and uncovering intake to the chamber and the exhaust port out of it. The air and the fuel rushing up force out the exhaust which has a scavenging effect pulling more air and fuel under the chamber until the piston once again closes things off. Then, the air and fuel are compressed and ignited and the whole thing starts over again. So, that one power stroke does not have to carry itself as far as it has to in a four-stroke. That is the reason why you use multiple cylinders in 4-strokes for consistent power, whereas in 2-strokes, lesser cylinders do the job better. You are not making more power per power stroke in a two-stroke, but you are making twice as many power strokes in a 2-stroke. 2-stroke engines can work in multiple orientations, and that is the reason why they are used in chainsaws, lawnmowers, rickshaws, dirt bikes, and everything in between. Let us not forget the amazing bikes and scooters in India that used 2-strokes and let us not forget the amazing sound that they make.
But, if 2-strokes are so amazing, why are they not brought back, and why were they discontinued in the first place? 2 stroke engines don’t have valves like 4-strokes, so for the oil to lubricate, it will mix with the fuel before getting to the cylinder, so the fuel and oil cannot lubricate properly. And fuel and oil cannot combust efficiently during a power stroke. So, not only is it ineffective in lubricating the system, but it also means that the oil burns up in the combustion chamber. That means more air, more deposits, and more harmful emissions. So, 2-stroke engines don’t last generally as long as 4-strokes, because they wear out because of the inefficient lubrication system. 2-strokes are also not as fuel-efficient as 4-strokes because of not having a consistent air-fuel mixture. That is the reason why 2-strokes are only used in applications where the motor is not used all the time.
So, do you think that 2-strokes should make a comeback? I think, yes, because the 2-stroke legends from the past are calling us, for one more chance at shining in glory, and their call, is hard to ignore.
