Timing chain or timing belt? Differences, advantages, failures…

When buying a vehicle, whether new or used, it is worth considering whether it uses a timing chain or a timing belt, as well as its maintenance intervals.

When we talk about what type of timing system our engine has, we are often unaware of the importance this engine component has, or of what poor maintenance entails. We will try to explain the most important points about this component in a very simple way.

The first thing we need to know is what the timing system is, whether chain or belt, in our engine, and why this component is necessary.

An engine’s timing system controls the movement of the camshafts (usually located in the cylinder head), which in turn operate the valves that allow the different phases of a combustion engine to take place. These include the intake phase of the air-fuel mixture (or just air in a direct-injection engine) and the exhaust phase to expel the burned gases. This timing is achieved through synchronization with the rotation of the crankshaft and the movement of the pistons.

Therefore, the function of this belt or chain is to transmit motion from the cylinder head to the block. Its main difference is constructive.

• Belt. It is a strip made of rubber, rubber compound and nylon, with a smooth side (outer surface) and a toothed side (inner surface) to engage with the pulleys on the cylinder head and the crankshaft.
• Chain. Made of a metal alloy, very similar to a bicycle chain but more robust, it meshes with the sprockets on the cylinder head and crankshaft.

So far we know what both the timing belt and the timing chain are and what they are for. But, in practical terms, what is the difference?

Timing belt

As we have said, it is made of rubber, rubber compound and nylon. Therefore, to avoid problems in our engine, we must carry out maintenance which, according to the manufacturer’s specifications, will fall roughly between 80,000 and 220,000 km. Usage and climate will also influence this interval.

Be careful, because all manufacturers also set a replacement period for the timing belt in years, usually 10, at which it must be changed even if the mileage has not been reached. This is because the belt deteriorates through “ageing” of the materials. Many owners ignore this maintenance period on the excuse that they do few kilometres. And in the end, what happens, happens.

Among the advantages of the belt, due to the material it is made from, the noise it produces in operation is usually much lower than that of a chain, so the dB level of our engine will be reduced. Another advantage is constructive. The belt allows more flexibility than the chain when using its movement to drive other engine components, such as the alternator.

Among the disadvantages, as already noted, is its maintenance. The biggest problem we can face if our engine has a timing belt and it is not properly maintained is its breakage, which has fatal consequences for the engine. And it is clear that belts, through wear or deterioration, and if we are not attentive to when they need replacing, can lead us to this misfortune.

The average cost of a timing belt replacement on a compact car, depending greatly on each manufacturer, is around 800 euros. It is not only the belt that is recommended to be changed; the tensioners are also recommended, and in many cases the water pump must be replaced at the same time.