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A valve tappet, also known as a valve lifter or cam follower, is a crucial component of an internal combustion engine. Here are its uses and functionalities:

1. Transferring Force: The primary function of a valve tappet is to transfer force from the camshaft to the pushrod (in a pushrod engine) or directly to the valve itself (in an overhead camshaft engine). This motion opens the valve, allowing fuel and air into the combustion chamber or expelling exhaust gases.

2. Maintaining Zero Valve Clearance: In engines with hydraulic lifters, the lifter also serves to automatically maintain zero valve clearance to keep the valve train quiet and to allow for thermal expansion of engine components.

3. Reducing Wear: The tappet surface is specially designed to be hard and smooth, reducing wear from the camshaft lobe's constant friction.

4. Noise Reduction: In addition to reducing wear, the tappet's smooth operation also serves to minimize noise produced by the valve train.

Valve tappets can be either solid (requiring manual adjustment of valve clearance) or hydraulic (automatically adjusting for valve clearance).

In terms of applications, valve tappets are found in nearly all types of internal combustion engines, including those in cars, motorcycles, trucks, heavy machinery, and some aircraft. Their design can vary depending on the specific engine configuration and the demands placed upon the engine.

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