What is timing belt

What is a timing belt and what is the function of a belt in it

The gas distribution mechanism (abbreviation GRM) is a mechanism that provides the inlet and outlet of the working fluid in internal combustion engines. Simply put, it controls the valve timing, being responsible for the timely supply (injection) of the fuel-air mixture into the working cylinders and the release of exhaust gases from them.

The timing belt (abbreviated timing) is responsible for synchronizing the crankshaft and camshafts. This ensures an exact match of the engine's operating cycles: the valves open and close exactly at those moments that correspond to one or another position of the piston.

Most modern cars are equipped with four-stroke internal combustion engines, the operating cycle of which has four phases - intake, compression, power stroke and exhaust.

For normal engine operation, it is necessary to control the movement of the pistons inside the cylinders and precisely synchronize it with the opening and closing of the intake and exhaust valves. Without proper timing, the engine simply cannot function. This task is performed by the gas distribution mechanism (GRM).

The purpose of the timing is to fill the cylinders with an air-fuel mixture and remove exhaust gases at strictly defined moments.

The control element of the timing is the camshaft, the cams of which open and close the valves. In order for the camshaft to perform its function, it needs to be rotated. This is exactly what the belt does, which transmits torque from the crankshaft. For every complete engine cycle, the camshaft rotates once and the crankshaft rotates twice.

In addition to synchronizing the crankshaft and camshaft, the timing belt in many cases also ensures the operation of the water pump.

In most cases, the belt is additionally covered with a casing to prevent dirt, sand or snow from getting on it. However, getting to it for inspection or replacement is usually not difficult.

The timing belt looks like a wide ring with teeth on the inside. It is made from rubber, to which fiberglass or polymers are added to increase wear resistance and heat resistance.

Reasons for failure

Despite the strength of modern timing belts, they are nevertheless subject to wear.

Many drivers do not properly monitor their condition and ignore the replacement intervals recommended by manufacturers. As a result, natural wear ends with a break.

Serious trouble can be caused by oil or other liquid getting on the belt, which will cause slippage and, accordingly, engine malfunction. Ultimately, everything will end in a cliff. Foreign liquid is unlikely to be reliably and completely removed, so the belt should be replaced as soon as possible in such a situation.

In addition, the water pump, rollers and mechanical or hydraulic tensioners can also be a source of problems, the condition of which also needs to be monitored.

The consequences of the cliff

When the timing belt breaks, the camshaft immediately stops rotating and stops controlling the valves, which freeze in the state they were in at the time of the break.

Next, the pistons hit the valves, deforming them. The pistons themselves may be damaged. A chain reaction can lead to failure of the camshaft, cylinder head and other engine parts. All this will result in an expensive repair of the unit, and in some cases can lead to an accident.

Fortunately, a broken timing belt most often occurs when starting the engine at the time of the initial jerk. If this happens at low speeds, then irreparable damage will most likely be avoided and the matter will be limited to damage to the valves or their guides.

All this is true for so-called interference engines, in which the pistons and valves share some common space, but never collide during normal operation. This design is a kind of payment for increased power and efficiency. These are many gasoline and most diesel units. If your engine is without interference, then if the rubber drive breaks, it is enough to replace it and you can continue driving.

Advantages and disadvantages of belt and chain transmission

In addition to a rubber belt, a metal chain can be used to transmit rotation from the crankshaft to the camshaft, which looks like a bicycle chain.

The chain is much more expensive than the belt, but it has a much longer service life. Usually, manufacturers recommend replacing it after a certain mileage, and some argue that the chain does not need to be replaced at all. It all depends on the specific car model.

Although the degree of wear of the chain, unlike the rubber belt, is difficult to assess visually, but a damaged metal drive will make itself felt by knocking when the engine is cold. And an unexpected break in the circuit is practically excluded.

Compared to a belt, the chain is not affected by temperature fluctuations and aggressive driving style.

The disadvantages include noise during operation and the need for periodic lubrication.

Another feature of the chain drive is hydraulic tensioners, which are controlled by engine oil pressure. If for any reason the oil pressure drops, the chain tension may be broken. The links of a loose chain can slip on the pulley teeth, resulting in unstable engine operation.

When to change the timing belt

Like other consumable parts and materials, the timing drive should be replaced with a new one in a timely manner. This item is not repairable. Pulling with a replacement is an extremely risky business. Elementary care and relatively low costs will help to avoid overhaul or replacement of the engine, the cost of which is comparable to the cost of the car itself.

The recommended interval for changing the timing belt depends on the machine model and engine type. European manufacturers usually indicate mileage in the range of 70-100 thousand kilometers, although there are exceptions, both upward and downward. In Ukrainian conditions, it is better to focus on 50 thousand.

But often the rubber timing drive needs to be replaced earlier than these dates. It can stretch and sag, and cracks may appear on it. This can be seen by visual inspection. During the inspection, it is necessary to make sure that the belt is properly tensioned, and the teeth are not worn out and have a reliable engagement with the gears of the shafts. Do not allow any oily liquids to come into contact with the drive. Even a small amount of oil will cause slippage.

When buying a timing belt, pay attention to the markings. The drive must be compatible with your engine, have the correct number of teeth, pitch and width.

The belt must be reliable, durable, resistant to stretching and withstand exposure to elevated temperatures. Therefore, avoid products of dubious origin and unknown quality.

In order not to do the work again later, at the same time it is worth replacing parts that have approximately the same resource - rollers, tensioners, and also a water pump if it is driven by a timing belt.