The tappet plays an essential role in ensuring that the engine runs efficiently, but what is it, and how does it work?
A tappet is a small cylindrical component located in the engine block. Its main function is to transfer the movement of the camshaft to the engine valves, allowing them to open and close at the correct time.
The tappet operates by following the motion of the camshaft, which has a series of lobes that push against the tappet at specific intervals. As the camshaft rotates, the lobes lift the tappet, which in turn pushes the push rod and rocker arm, causing the valve to open and close.
There are two main types of engine tappets: mechanical tappets and hydraulic tappets.
Mechanical tappets are solid tappets that require manual adjustment to maintain proper valve clearance. Valve clearance is the space between the rocker arm and the valve stem when the valve is fully closed. Mechanical tappets require periodic adjustment to ensure proper valve clearance.
Mechanical tappets consist of a solid metal body which is in direct contact with the camshaft. When the camshaft rotates, it lifts the tappet, which in turn opens the valve.
The valve clearance on mechanical tappets is adjusted by turning a screw at the top of the tappet. This screw controls the tappet height and thus the clearance between the valve stem and rocker arm.
In general, mechanical tappets are still commonly used in many engines, especially in high performance applications. They offer a simple and reliable design that can withstand high engine speeds and heavy loads. However, they require more maintenance than hydraulic tappets and can be noisier to operate.
Hydraulic tappets are used in many modern internal combustion engines. These tappets are designed to automatically compensate for valve clearance.
They consist of a small cylindrical body which houses a piston and a spring. The piston is located between the push rod and the rocker arm, and the spring keeps the piston in contact with the camshaft. When the camshaft rotates, it lifts the tappet, causing the piston to compress the spring and create an oil pocket inside the tappet.
An advantage of hydraulic tappets is their ability to reduce engine noise and vibration. Because hydraulic tappets automatically adjust to compensate for valve lash, there is less valve train clearance, which reduces noise and improves overall engine performance.
However, hydraulic tappets also have some disadvantages. They can be more complex than mechanical tappets and require precise fabrication and assembly to function properly. Hydraulic tappets are also susceptible to oil contamination, which can cause them to fail and damage the engine.
WHEN SHOULD YOU CHOOSE ONE OR ANOTHER?
The choice between hydraulic and mechanical tappets depends on a number of factors, such as engine design, intended engine use and the performance objectives of the engine builder or owner.
In general, hydraulic tappets are used in modern engines and in applications where ease of maintenance and quiet operation are important. Hydraulic tappets are commonly used in passenger car engines, as well as in many small and medium-sized marine engines. They are also commonly used in diesel engines, as they provide good control of valve timing and are less prone to wear than mechanical tappets.
Mechanical tappets, on the other hand, are used in many high performance and racing applications. They are generally preferred by performance enthusiasts as they can operate at higher revs and provide more precise control over valve timing. These tappets are also used in racing engines designed for maximum power and torque.
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