Which is the Best Engine Valvetrain Design? OHV, SOHC, DOHC or Flathead | Pros and Cons

Summary

This video delves into the complex workings of the valve train in internal combustion engines, explaining its components such as the camshaft, valves, springs, lifters, push rods, rocker arms, and timing mechanisms. The valve train's role in regulating intake and exhaust valve timing is crucial for efficient combustion and engine performance. Various engine designs, such as overhead valve, overhead camshaft, and flathead engines, are explored, highlighting their differences, benefits, and historical significance. The video provides a comprehensive understanding of engine functionality, covering both modern and vintage engine technologies.

Takeaways

• 😀 The valve train in an internal combustion engine regulates the opening and closing of intake and exhaust valves for efficient combustion and engine performance.
• 😀 The key components of the valve train include the camshaft, valve, valve spring, lifters, push rods, rocker arms, and timing mechanism.
• 😀 The camshaft rotates at half the speed of the crankshaft, and its specially shaped lobes control valve opening and closing with precise timing.
• 😀 Valve springs ensure proper seating of the valves and prevent them from floating during high engine speeds.
• 😀 Lifters (tappets) transfer the motion from the camshaft lobes to the valves, while push rods transmit this motion to the rocker arms in overhead valve engines.
• 😀 Rocker arms convert the linear motion of push rods into the necessary pivoting motion to open and close the valves.
• 😀 The timing mechanism synchronizes the camshaft with the crankshaft to ensure precise valve timing, which is crucial for engine efficiency and performance.
• 😀 Different valve train configurations include overhead valve (OHV), overhead camshaft (OHC), and dual overhead camshaft (DOHC), each offering different benefits in terms of engine performance and efficiency.
• 😀 Overhead valve engines are lighter, cheaper to produce, and offer high torque at lower RPMs, but have limited maximum RPM capabilities.
• 😀 Dual overhead camshaft engines offer improved airflow, higher RPM capability, and better performance due to more precise control over valve timing and lift.
• 😀 Flathead engines, which were widely used in early cars, have valves located within the engine block, limiting airflow and performance compared to modern engine designs.

Q & A

What is the primary function of the valve train in an internal combustion engine?

The valve train manages the opening and closing of the intake and exhaust valves, regulating the timing of these operations to ensure efficient combustion and optimal engine performance.

What role does the camshaft play in the valve train?

The camshaft is a rotating shaft that contains specially shaped lobes designed to open and close the valves with precise timing. It is driven by the engine's crankshaft and ensures that the valves operate at the correct moments during the engine's cycle.

How do valve springs contribute to engine performance?

Valve springs are helical springs placed around the valve stems. They ensure the proper seating of the valves and prevent them from floating at high engine speeds, maintaining efficient valve operation.

What is the function of lifters (tappets) in the valve train?

Lifters, or tappets, transfer motion from the camshaft lobes to the valves. They are cylindrical components that ride on the camshaft, actuating the intake and exhaust valves to control airflow into and out of the combustion chamber.

What is the purpose of push rods in the valve train?

Push rods are long, slender rods that transfer the upward movement of the lifters to the rocker arms, typically in overhead valve engines. They help transmit motion from the camshaft to the valves in the cylinder head.

What are rocker arms, and how do they function in the valve train?

Rocker arms are pivoting levers that convert the linear motion of the push rods into the required pivoting motion to open and close the valves, ensuring precise valve timing in the engine.

Why is maintaining proper valve timing crucial for engine performance?

Proper valve timing ensures efficient combustion and optimal engine performance. If the timing is off, it can lead to decreased power, poor fuel efficiency, and potential engine damage.

What is the difference between overhead valve engines and overhead camshaft engines?

Overhead valve engines use push rods and rocker arms to operate the valves, while overhead camshaft engines position the camshaft above the combustion chamber, directly controlling the valves. Overhead camshaft engines tend to offer better performance at higher RPMs.

What are the advantages of a dual overhead camshaft (DOHC) engine over a single overhead camshaft (SOHC) engine?

A dual overhead camshaft engine has two camshafts per bank of cylinders, allowing for more precise control over valve timing and better engine breathing. This results in improved performance, higher RPM capabilities, and greater power output compared to a single overhead camshaft engine.

Why did Flathead engines become less popular in modern vehicles?

Flathead engines, while simple and affordable, have limitations in combustion efficiency and power output due to their valve design. These limitations, along with lower compression ratios and restricted airflow, led to the decline in their use as more efficient engine designs emerged.