MDE Unit 3 Q6

A larger than specified tappet clearance on an exhaust valve in a diesel engine can lead to several negative consequences:

Reduced Valve Lift

• Insufficient exhaust gas expulsion: With reduced valve lift, the exhaust valve doesn’t open as fully, hindering the efficient removal of exhaust gases from the cylinder.
• Decreased engine performance: This results in a loss of power and torque due to incomplete combustion.

Delayed Valve Opening and Closing

• Disturbed combustion process: The delayed opening and closing of the exhaust valve can disrupt the normal combustion cycle, leading to inefficient fuel burning and increased emissions.
• Increased back pressure: The delayed closing of the exhaust valve can create higher back pressure in the cylinder, affecting engine breathing and performance.

Mechanical Issues

• Valve and seat damage: The reduced valve lift and delayed closing can cause excessive wear on the valve and its seat, leading to premature failure.
• Increased noise: The loose valve can create a clattering noise, indicating the problem.
• Valve float: In extreme cases, at high engine speeds, the valve might not fully close due to insufficient spring force, leading to catastrophic engine damage.

In summary, a too-large tappet clearance on the exhaust valve of a diesel engine can lead to reduced engine performance, increased emissions, and potential mechanical damage. Regular inspection and adjustment of valve clearances are crucial for maintaining engine health and efficiency.

A tappet clearance that is smaller than specified can cause severe damage to a diesel engine. Here’s how:

Premature Valve Opening and Closing

• Valve float: Due to the reduced clearance, the valve may open prematurely as the engine speeds up. This is known as valve float.   1. SpinTron Secrets: Valve Float, Bounce, and Loft Explained! – Trend Performance blog.trendperform.com
• Valve clash: In the worst-case scenario, the valve may not fully close, leading to a collision with the piston, resulting in catastrophic engine damage.

Overheating

• Insufficient cooling: With the valve opening prematurely and closing late, there’s less time for the valve to cool. This can lead to overheating and potential valve burning.

Reduced Engine Performance

• Incomplete combustion: Incorrect valve timing due to too small a clearance can disrupt the combustion process, leading to reduced power and increased fuel consumption.
• Increased emissions: Incomplete combustion also results in higher levels of harmful emissions.

Mechanical Damage

• Valve and seat damage: Overheating and premature opening/closing can cause excessive wear on the valve and its seat, leading to engine failure.
• Increased engine noise: A small clearance can cause a clicking or ticking noise from the engine.

In summary, a tappet clearance that is too small can have devastating consequences for a diesel engine. It’s crucial to maintain the correct clearance to ensure optimal engine performance and longevity.

A double nested spring is a spring assembly consisting of two springs placed one inside the other. This configuration is commonly used in applications requiring higher spring rates or increased load capacity compared to a single spring.  

1. Compression Springs in Parallel – Mid-West Spring & Stamping

Key characteristics of a double nested spring:

• Increased spring rate: By combining two springs, the overall stiffness of the system is increased.
• Improved load capacity: The combined springs can handle higher loads compared to a single spring.
• Reduced spring wire diameter: Using two smaller springs can often be more cost-effective than producing a single spring with the same characteristics.
• Enhanced durability: In some cases, double nested springs can offer improved durability by distributing the load across two springs.

Common applications:

• Valve springs in internal combustion engines   1. Compression Springs in Parallel – Mid-West Spring & Stamping www.mwspring.com
• Clutch springs
• Suspension systems

Image of a double nested spring:

Opens in a new windowwww.mwspring.com

double nested spring

Double valve springs, or nested valve springs, are used in internal combustion engines to enhance performance and reliability. Here’s why:

Increased Spring Rate

• Higher valve lift: Double springs provide a combined spring rate greater than a single spring, allowing for higher valve lifts, which can improve engine performance.
• Improved combustion: Higher valve lift can lead to better volumetric efficiency, resulting in more efficient combustion.

Improved Durability

• Reduced stress: By distributing the load over two springs, the stress on each individual spring is reduced. This increases the life of the springs and reduces the risk of spring failure.
• Consistent valve control: Double springs provide more consistent valve control at high engine speeds, preventing valve float.

Higher Engine Speeds

• Valve control: The increased spring rate allows the engine to operate at higher speeds without compromising valve control.
• Improved performance: Higher engine speeds can lead to increased power and torque.

Aggressive Cam Profiles

• Valve lift requirements: Double springs can accommodate more aggressive cam profiles with higher valve lifts, which can improve engine performance.

In summary, double valve springs offer several advantages over single valve springs, including increased spring rate, improved durability, higher engine speeds, and the ability to use more aggressive cam profiles. These factors contribute to better engine performance and reliability.