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Valve timing is crucial for internal combustion engines to function properly. The camshaft rotates and opens/closes the valves via pushrods and rocker arms. Valve timing can only be adjusted by repositioning the cams. Ignition timing is often confused with valve timing, but it is responsible for firing the cylinders at the right moment.
In internal combustion engines, there are at least two valves for each cylinder: an intake valve and an exhaust valve. In order for the engine to function properly, the intake valve must draw fuel and air at the proper time, the cylinder fires, and then the exhaust valve must open to allow the burned fuel to escape so the cycle can repeat itself. In order for the engine to function properly, the precise actuation of these valves, in the proper sequence, is valve timing.
In most engines, when the cylinders fire, they exert force on the camshaft, causing it to rotate and perform a number of functions. It powers the transmission and other components of a vehicle, such as the alternator and water pump. Also, as the name suggests, the camshaft has a series of cams along its length.
These cams press devices called pushrods which in turn push up devices called rocker arms. The rocker arms serve as levels to depress and lift the spring-loaded engine valves. This action opens and closes the valves at the right time to keep the engine running smoothly.
The mechanical nature of engine valve systems means there are limited ways to adjust valve timing. There is usually only one way: take the engine apart and reposition the cams on the camshaft that begin the sequence to actuate the valves. However, other problems can look like inaccurate valve timing.
A bent pushrod or valve stem can cause a valve to not fully open or close when required. These types of problems are not actually related to valve timing, but just cause symptoms that appear to be timing related. The valves are actuating correctly at the right time; they simply cannot perform their functions due to physical damage. These problems also cannot be adjusted, instead requiring the replacement of any faulty components.
Engine ignition timing is often mistakenly thought to be responsible for bad valve timing; However, this is not the case. While it is true that faulty ignition timing can cause cylinders to fire while the valves are not in their proper positions, the valve timing itself, which is set by cams on the camshaft, does not have the blame. The ignition timing is to blame.
Ignition timing is responsible for sending power to the spark plugs, which fire the engine’s cylinders. Ignition systems know when to send power to the plugs, based on settings that inform them of the physical location of the cylinders and valves. When set correctly, ignition timing fires the cylinders at the exact moment the valves are in their correct positions.
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