How does the Valvetrain works?

The valvetrain, in an automobile engine what allows fresh air (or alternatively air-gas mixture, if the engine employs a carburetor) to enter and exhaust gases to abandon the combustion chamber. In fact, the valvetrain is not a single piece, rather is a set of different parts, like the camshafts, the valves, springs and chains, or in an alternative, pushrods, rocker arms and lifters. What allows for different valvetrain speeds is the connection between said camshafts and the crankshaft, this can be done by the mean of gears, chains or alternatively belts.

Most engines nowadays are cam driven, making the focus of this article said valvetrain system.

The valves are commonly of the poppet type, mechanism which allows gases in and out of the combustion chamber. Oftenly It exhibits a round shape, that may vary to an oval, at one end of a shaft, known as valve stem. When used as intake, the different pressures of the exterior and interior of the cylinder, help actuate the valve, likewise, when employed as an exhaust valve the pressure within the cylinder aids the valve to be sealed until the time of its opening.

The Poppet Valve, the most usual in an automobile’s engine


The camshaft are the command unit of the valves, as is their function to control the lift of the valves, as the name refers, this part takes the form of a shaft, with lobes, the part that connects with the valves. The lobes allow for the opening of the valve, and accordingly to their height and broadness, cause the valve to have a larger lift (if the lobe is taller) or maintain itself opened for longer (if the lobe is broader).

Example of a Camshaft. Mention to the lobes, that control the lift of the valves, and their arrangement, controlling the moment of the lift.

The timing chain serves the role of controlling the speed at which the camshaft rotates, and therefore, the frequency of the opening and closing of the valves. The timing chain connects a gear in the camshaft and the crankshaft. The effects are obvious – as the engine accelerates, the crankshaft spins faster, therefore, being connected to said piece, cams rotate faster or slower, always matching the engine speed. This function can also be taken not by a chain, but a belt or even gears to rotate the camshaft, as seen in the pictures below.

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