Two-Stroke Engine And Four-Stroke Engine Differences in Motorcycle

The engine is the brain of the motorcycle, responsible for generating power and thrust for the motorcycle to move forward. Needless to say, the engine is one of the most important components of a motorcycle. While most motorcycle enthusiasts know about their bike riding accessories, the same can not be said about their motorcycle’s engine. It is crucial for every motorcycle rider to understand their bike’s engine for a variety of reasons.

Generally, a motorcycle engine is divided into two categories, a two-stroke engine and a four-stroke engine. Strokes refer to the upward and downward movement of the piston while generating energy. In this blog, we will guide you through the difference between four-stroke engine and two-stroke engine and their pros and cons, to help you figure out which is the best choice for your bike riding needs.

A] What Is An Engine? 

The engine is responsible for converting the stored fuel into mechanical energy. An engine consists of a piston, spark plug, engine valves, cylinder heads, and crankshaft, among a few other things. Bike engines are usually distinguished by the number of piston cycles.

The two-stroke and four-stroke engines used in bikes are a type of reciprocating piston engine. These pistons move up and down capturing air and mixing them with fuel to create ignition. The intense pressure and temperature caused by this ignition convert into mechanical energy.

B] What Is A Two-Stroke Engine?

The two-stroke motorcycle engine is usually used for bikes that require less power. The entire combustion cycle of the engine is covered in a single crankshaft revolution. The combustion cycle of the two-stroke engine consists of 2 strokes of the piston, the intake-ignition stroke and the compression-exhaust stroke.

During the intake-ignition stroke, the piston moves upward to create a vacuum in the chamber, forcing the air inside along with fuel. The piston compresses the air-fuel mixture with immense speed causing the spark plug to ignite the fuel. A high-quality spark plug, such as NGK Iridium Spark Plug Set for Pulsar NS200 makes the process of combustion easier and safer.

After this, the combustion compresses the piston down, thus generating power in the engine. As the pistons move downward to the engine cylinder, it exposes the exhaust port. The remaining gas and fumes are then released back into the air through the exhaust port. The difference between two-stroke and four-stroke engines is that two-stroke engines operate on a simpler principle with fewer steps.

C] What Is A Four-Stroke Engine?

The difference between 2-stroke and 4-stroke engines is that 4-stroke engines require 4 complete cycles, i.e. two crankshaft revolutions to complete a power cycle. The four strokes are divided into intake, compression, power, and exhaust. Four-stroke engines are mostly used in modern bikes as they offer better smoke management, less torque, and better thermal management.

• The first stroke moves the piston down the cylinder opening the intake valve. Air is then drawn into the cylinder, while fuel is drawn in from the fuel injection system. 
• Secondly, the intake and exhaust valves are closed and the air-fuel mixture in the cylinder is compressed. 
• During the third stroke, the spark plug ignites the fuel-air mixture, creating an explosion. The explosion powers the crankshaft by forcing the piston down, moving the back wheel forward. Invest in a quality fuel injection optimiser, such as the FuelX Pro Fuel Injection Optimizer for maintaining your engine’s health. 
• Finally, the remaining gasses from the combustion are let out through the exhaust valve as the piston travels upwards. The entire cycle is then repeated over and over.

D] Difference Between 2-Stroke And 4-Stroke Engine

• The difference in the number of strokes: The main difference between 4-stroke and 2-stroke engines is that a piston has to travel upward and downward only once, (two strokes) to generate power in 2-stroke engines, while the piston has to travel upward and downward twice as many times in 4-stroke engines.
• Completeness of the engine’s cycle: A 2-stroke engine completes one engine power cycle within a single crankshaft revolution. While a 4-stroke engine takes two crankshaft revolutions to complete one engine power cycle.
• Lubrication: 2-stroke engine lubricates by mixing oil with the fuel as it does not have a separate oil system. This makes them use more lubricating oil, as most of it burns with fuel. Meanwhile, 4-stroke engines have a separate oil system for lubrication, requiring less oil.
• Efficiency: 2-stroke engines generate less power while creating a lot of noise and heat. This makes them very inefficient by modern standards. The 4-stroke engine utilises fuel efficiently to create the most power possible. 
• Power: Two-stroke engines provide a higher weight-to-power ratio, making them the perfect choice for lightweight bikes. The power output of four-stroke engines is smoother with better torque, making them suitable for heavier and faster bikes.
• Design complexity: The design of two-stroke engines is relatively simple, making them easier to maintain, if you get stuck while on the road. Four-stroke engines are more complex with more moving parts and require special maintenance. 
• Applications of both engines: The two-stroke engines have limited applications such as lightweight bikes. Whereas four-stroke engines have a wider range of applications in the motorcycle industry. Here is a comparison of United 125cc and Honda CG125cc bikes, both of which are powered by 4-stroke engines.

E] Pros And Cons Of Two-Stroke Engine 

Pros

• Two-stroke engines are generally lighter, making them the perfect choice for lightweight motorcycles, such as trail and commuter bikes.
• They take less space and have fewer parts.
• They are easy to repair and maintain.
• Two-stoke engines have a simple design, making them comparatively cheaper.
• They have a high power-to-weight ratio, offering great speeds for lightweight bikes.
• The engine is not affected much by extreme external temperatures and works well in every weather condition.
• It has higher torque offering better acceleration.

Cons

• Two-stroke engines are inefficient at fuel consumption, as a significant portion of fuel remains unburnt and leaks from the exhaust.
• It has poor thermal management.
• The exhaust system is made up of thin-walled pipes which get damaged easily.
• It also creates a lot of smoke and fumes, which get stuck in the exhaust pipe, making it dirty. The Red Rooster Performance Stellar Exhaust offers free-flow exhaust which provides a 20% boost in performance.
• The release of unburned fuel into the air is pretty detrimental to the environment.
• It does not have a separate oiling system; hence, oil needs to be mixed with fuel for lubrication. 
• It consumes more oil as most of it burns during combustion.
• It creates a lot of noise.
• The engine wears out more frequently as compared to four-stroke engines.

F] Pros And Cons Of Four-Stroke Engine

Pros

• Four-stroke engines offer smoother and better power stroke and torque at lower RPMs.
• They are fuel efficient, burning most fuel that enters the piston chambers.
• They also have a separate lubrication system for oiling, not requiring oil to be mixed with the fuel.
• They last longer due to less wear and tear.
• Better engine braking is a desired trait that four-stroke engines offer.
• It emits less fumes, making it environmentally friendly. Refer to the article “Two stroke or four stroke?” by India Environment Portal for more information on which engine is greener.

Cons

• Four-stroke engines are heavier and require more space.
• The four-stroke engine has more moving parts and, hence is very complex.
• This also makes it difficult to maintain and service the engine.
• It generated less torque, as compared to two-stroke engines.

Conclusion

Both the two-stroke engines and four-stroke engines work on the same combustion principle. They both offer unique features and benefits; hence, you must decide for yourself, which suits your needs. You can weigh the pros and cons written above to understand which one suits your riding style the best.

Four-stroke engines are found in most modern bikes; however, if you like to ride old school you can go for a bike with a two-stroke engine. While two-stroke engines are old-school, you can fix their problems with modifiers, such as new-age spark plugs, exhausts, and fuel injection. Visit Bikester Global Shop today to get a wide range of motorcycle accessories.