The toothed belt has a number of advantages over the drive chain. The latter is clearly more expensive. A timing belt is much simpler to manufacture than a chain. Essentially, a timing belt is a closed band of oil- and petrol-resistant rubber, reinforced with nylon cord with vulcanized teeth. If you compare a belt with a chain, the comparison will not be in favor of the latter. The belt is significantly lighter than the chain, which, naturally, cannot but affect the weight of the engine. In addition, the belt-driven motor is much quieter than its chain-driven counterpart. And the "rubber" is mounted outside the engine casing, which affects the time of its installation or replacement. For example, replacing the timing belt on a four-cylinder, eight-valve engine, followed by reinstalling it according to the timing marks, takes about 25–30 minutes. This trick won't work with a chain.
With proper maintenance, the timing belt will last a long time. As a reminder, domestic manufacturers offer a 60,000 km mileage warranty, while foreign manufacturers offer even more. Rover has managed to extend the belt replacement period to 160,000 km.
What does proper belt drive maintenance involve? The belt tension should be checked at least every 15,000–30,000 km. However, this does not mean that you just need to bend the cover and check if the belt is in place. It is best to inspect it after removing it from the engine. Sometimes it is difficult to notice that one of the teeth is cut. If this has already happened, then rest assured that it will not last long. Therefore, after removing the belt, make a mark on it with chalk, and then inspect it tooth by tooth. After installation, it is also necessary to check the position of the guide and tension rollers. All these elements must be in the same plane, otherwise the belt will operate at an angle, which will significantly reduce its service life.
An important factor for the operation of the belt is the absence of oil on its surface. No matter how oil-resistant the rubber the belt is made of, it's still not a case of "you can't spoil porridge with butter." Here, the oil actually does harm. Therefore, it is necessary to periodically pay attention to the condition of the camshaft and crankshaft seals. And if you notice an oil leak, try to fix it as soon as possible. As practice shows, keeping a belt in oil reduces its service life by half or even three times.
If this control is ignored, the consequences will not be long in coming. After 40,000–50,000 km, the belt will become loose due to stretching, causing it to begin to "whip." As a result, the "heavy" camshaft rotates out of sync with the crankshaft, but with a lag. This "asynchronous" operation results in further weakening of the belt tension. This results in excessive load on the teeth.
[The article is copied from the resource: MazBook.ru]
Caution! If several teeth break in a row, the camshaft may suddenly become stationary while the crankshaft rotates. It is at this moment that the open cylinder valves will "meet" the pistons. The result is a broken stem or bent valve, broken guide bushings, broken camshaft. There are, however, exceptions when the break occurs almost painlessly. However, this is only possible on those cars whose engines have piston grooves specially made for this case. These include, for example, our VAZs, namely cars VAZ-2105 with a 1300 cm³ engine and VAZ-2109 with a 1500 cm³ engine.