What’s a valve train?

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The valve train opens and closes an engine’s valves, allowing air and fuel to enter and exhaust to exit. There are three common designs, with the overhead cam being most popular. A malfunctioning valve train can cause engine misfires and damage.

A valve train consists of all the parts in an internal combustion engine that open and close the engine’s valves. Without the valves, the engine cannot receive the air and fuel needed to power the car. The valves also allow used fuel-air mixture to exit through the exhaust system after combustion. A valve train generally consists of the valves themselves and the camshaft used to turn them. Other parts vary depending on the specific design, but each performs a specific function by moving the valves.

When the engine needs to make power, it must do so by pressing a fuel-air mixture into a small space and igniting it with a spark. The engine’s cylinders do this work inside a closed chamber. To allow air and fuel to enter this chamber, a valve opens. Once the mix is ​​in, the valve closes to create a tight seal. After the mixture ignites and releases energy to turn the car’s wheels, a different valve opens to allow the exhaust to escape.

Three different common designs are used to make the valve train work, with the overhead cam being used most often on newer vehicles. In this type of valve train, small lobes on the camshaft push against the valves as the camshaft rotates, causing the valves to open temporarily. The camshaft is connected by gears or belts to the crankshaft, allowing it to rotate in time with the engine. This ensures that the valves open and close on time and prevents engine breakdown. Other versions of the overhead camshaft use additional parts instead of lobes to open and close the valves.

The second type of camshaft design is the block cam. It works in the same way as the overhead camshaft and opens the valves by pressing them or by activating additional parts to do the job. The difference is that the cam-in-block design places the camshaft inside the engine instead of on top of it. Commonly, parts known as rocker arms and pushrods actuate the valves. The third design uses a camless engine, which works without the use of a camshaft and uses different methods, such as sensors, to activate the valves.

If the valve train is not working properly, it can cause an engine misfire. The explosion in the chambers can happen too early or too late. In either case, the engine does not produce as much power, and parts can be damaged over time by the force of the explosion. When a driver notices that the car’s engine is making less power, misfiring, or making strange noises, they should have the engine checked out by a mechanic to avoid causing expensive damage.

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