A toothed belt has a number of advantages over a chain. It is obviously more expensive. It is much easier to make a belt than a chain. By and large, it is a closed band of oil-resistant rubber, reinforced with a nylon cord with vulcanized teeth. If you compare it with a chain, the comparison will not be in favor of the latter. The belt is much lighter than the chain, which, naturally, cannot but affect the weight of the engine. In addition, an engine equipped with a belt is much quieter than its brother equipped with a chain. And the "rubber" is mounted outside the engine casing, which affects the time of its installation or replacement. For example, the author of these lines spends 25-30 minutes replacing the timing belt and then installing it according to the marks. This trick will not work with a chain.
With proper maintenance and control, the toothed belt lasts a long time. Domestic manufacturers, we recall, provide a mileage guarantee of 60 thousand km, foreign ones - even more. Rover managed to push back the belt replacement period to 160 thousand.
What is the correct control and maintenance of this simple device? The correct position and tension of the belt should be checked at least every 15-30 thousand km. However, this does not mean that you only need to move the cover and check if the belt is in place. It is best to inspect it by removing it from the engine. Sometimes it is difficult to notice that one of the teeth has torn. If this has already happened, then rest assured that it will not last. Therefore, after removing the belt, make a mark on it with chalk, and then "run" it tooth by tooth. After installation, it is also necessary to check the position of the guides and the tensioner. All these elements must be on the same axis, otherwise the belt will work with a skew, which will not do it any good.
An important factor for the operation of the belt is the absence of oil on its surface. No matter how oil-resistant the rubber is, this is not the case when "you can't spoil porridge with butter". Here, oil is harmful. Therefore, it is necessary to periodically pay attention to the condition of the seals. And if you notice an oil leak, try to eliminate it as soon as possible. As practice shows, the presence of a belt in an oily environment reduces its service life by half or even three times.
If this control is ignored, the consequences will not take long to appear. After 40-50 thousand km, due to the stretching of the belt, the required tension weakens and it begins to whip. As a result, the heavy camshaft rotates out of sync, but with a lag. This asynchrony of the engine operation leads to even greater weakening of the belt. As a result, excessive loads on the teeth occur.
A break in several teeth in a row can lead to the camshaft remaining stationary at one fine moment, while the crankshaft rotates. It is at such moments that the open valves meet the pistons. The result is a broken or bent valve, its broken bushings, a broken camshaft. There are, however, exceptions when the break occurs almost painlessly. However, this is only possible on those cars that have grooves in the pistons specifically for this case. These include, for example, our VAZs, namely cars with engines VAZ-2105, 1300 cm³, and VAZ-2108, 1500 cm³.
If the car is not equipped with such an engine, a belt breakage will cost the owner a pretty penny, associated with a major overhaul of the engine. For example, the cost of a belt on a BMW reaches $40. Repairing the engine on the same Saab will cost $5,000. For a VAZ "nine", a belt can be bought for $25. But repairing the engine will cost $400.
[This material is taken from a resource: ToyotaMan.ru]