Four-Stroke Motorcycle Engines A four-stroke motorcycle engine is a type of internal combustion engine that completes four distinct phases—intake, compression, power, and exhaust—in two full crankshaft rotations (720 degrees). This design is widely used in motorcycles due to its balance of efficiency, durability, and smooth power delivery. 1. Working Principle The four-stroke cycle operates as follows: - Intake Stroke: The piston moves downward, creating a vacuum that draws in an air-fuel mixture through the open intake valve. - Compression Stroke: The intake valve closes, and the piston moves upward, compressing the mixture to increase combustion efficiency. - Power Stroke: The spark plug ignites the compressed mixture, causing an explosion that forces the piston downward, generating power. - Exhaust Stroke: The exhaust valve opens, and the piston moves upward again, expelling burnt gases from the cylinder. This cycle repeats continuously, converting chemical energy into mechanical motion. 2. Key Components - Cylinder & Piston: The combustion chamber where fuel burns, and the piston transfers energy to the crankshaft. - Valves (Intake & Exhaust): Control the flow of air-fuel mixture and exhaust gases. - Camshaft: Operates the valves via a timing chain or belt, synchronized with the crankshaft. - Spark Plug: Ignites the compressed mixture at the optimal moment. - Crankshaft & Connecting Rod: Converts linear piston motion into rotational force. 3. Advantages - Fuel Efficiency: Better than two-stroke engines due to precise combustion and less unburned fuel loss. - Lower Emissions: Complete combustion reduces harmful exhaust gases. - Smooth Operation: Balanced power delivery with less vibration. - Durability: Longer lifespan due to reduced wear and better lubrication. 4. Disadvantages - Complexity: More moving parts (valves, camshaft) increase maintenance needs. - Higher Cost: Manufacturing and repairs are more expensive than two-stroke engines. - Weight & Size: Bulkier due to additional components. 5. Applications Four-stroke engines dominate modern motorcycles, from commuter bikes to high-performance sport bikes. They comply with strict emission norms while delivering reliable power across various riding conditions. Conclusion Four-stroke engines offer an optimal balance of efficiency, performance, and environmental compliance, making them the preferred choice for most motorcycles today. Their refined operation and adaptability ensure continued dominance in the industry.