How and what is the importance of measuring valve clearance?

15 de February de 2023 Technical Tips


Everyone knows that the engine is the vital component for the operation of the vehicle, responsible for generating force for the wheels and, consequently, keeping it moving.

It is not new that there are several internal components in the engine, such as: pistons, cylinder liners, guides, seats, camshaft, valve springs, tappets, rocker arms and valves. All of them, the Engine Expert can find them in our catalog.

But today we will only talk about the intake and exhaust valves. We will understand its operation, how to measure in case of engine valve clearance and the importance of always performing this measurement.

Valve function on engine

The valves as well as the other components of the assembly play an important role in the operation of the entire engine. They are responsible for controlling the entry and exit of gases from inside the cylinders.

In a combustion engine, two types of valves are required: inlet and exhaust valves.

In a four-stroke engine, the intake valves are responsible for the intake of fuel and air into the cylinder, while the exhaust valves are responsible for removing the gases from the fuel burn of the cylinder.

The components attached to the valves are composed of the well-known valve train, which you can learn more about in this other post.

Why should valve clearance be measured?

The importance of having precision of the opening timing of the valves is essential for the operation of the engine. It is important to check the clearance and/or calibration of valves to avoid noise, loss of power and, of course, fuel consumption and excessive emission of pollutants.

Through these symptoms, the Engine Expert will be able to identify the valve timing problem.

How to measure valve clearance?

First of all, it is important to know whether or not the engine requires periodic regulation of these valves.

NEVER use guesswork! Consult the manufacturer!

If the measurement is necessary, the first step is to know what are the conditions required to perform the adjustment (cold or hot engine), the necessary tools (some models require special devices), the procedure for performing the service, as well as the specifications of the clearances.

This information can be found in the vehicle’s service manual.

IMPORTANT POINT: IT will not make sense to perform the tune up procedure without previously checking the valve clearances when adjustable. Despite all the work of checking and adjusting the power and ignition systems, they may end up not having a desired effect, causing the problems mentioned above to continue to occur.

The engine expert should also give importance to other mechanical checks, such as: measuring the depression of the intake manifold, measuring the engine working temperature, checking the tightness of the combustion chambers, checking the quality of the fuel used, presence of false air in the intake ducts, etc.

It is always important to think that sometimes these symptoms of engine malfunction are not directly linked to a malfunction of the power and ignition systems.

However, if the engine is equipped with hydraulic tappets, the expert must turn all his attention to the quality and state of the lubricant used.

Remember: the proper functioning of this component depends directly on the stability of the pressure inside. Lubricants whose viscosity varies greatly, when subjected to a temperature rise, tend to cause internal leaks in the tappets.

The consequence of this is a significant change in the behavior of the valves.

In this case, the main symptom is a malfunction, combined or not with the appearance of noises in the high parts of the engine, which occurs only in hot operation.

And the hotter the engine gets, the more intense the symptoms.

The engine expert needs to know that lubricants contaminated by excess fuel tend to have their viscosity greatly reduced. Therefore, its periodic replacement must be taken very seriously, as well as the verification of fuel leaks into the crankcase.

If the quality does not meet the operating requirements of the engine, it will do no good to replace the lubricant at the right time.

In these types of engines, lubricants with a high viscosity stability index as a function of temperature are required.

This property is tested by the vehicle manufacturer. Therefore, if a particular make/model of lubricant is the recommended one for an engine, it is the one that should be used.


So, did you know this information about the engine valves? Do not forget that, at the time of maintenance, the greatest ally of the applicator is always a reliable supplier

RIO, which offers pieces of certified quality and guarantee of origin with the Orange Box that you already know!

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