The timing belt drive can, without special lubrication, low noise crankshaft and, mostly overhead, camshaft(s) be form-fitted at the ratio of 2:1 This form-fit must be maintained throughout it's entire lifespan. If only one tooth is skipped, the least that can happen is that the timing will be changed. In the case of the diesel engine nearly always, in the petrol engine very often, does it cause a destructive contact between the piston(s) and the valve(s).
In the meantime, the producers of drive belts have been put under immense pressure, because both the manufacturers and the buyers want to spare themselves the costly timing belt replacement by choosing the timing chain The further development of the timing belt has led to a lifespan of up to 240.000 km. What remains is the weight saving advantage, because timing belts are not only lighter, they also need neither a sealed area nor guide-rails. In the meantime, even oil-compatible examples are available.
On the rear side of the timing belt, other components (e.g., the water pump) can also be force-fittingly driven. It is not only found in the camshaft drive, it's even used in high-torque motorcycle engines (z.B. Harley Davidson) for the secondary drive. The area in which the timing belt works must not, in contrast to the timing chain, be sealed off from the outside world. Quite often a light, plastic covering as protection is sufficient.
The timing belt is made from synthetic material, which, on the drive-side, is strengthened by glas-fibre threads (previously steel wire) and the rear-side by polyamide material. A temperature resistant interlayer provides for good co-operation between the two. In addition, a certain material (e.g., polyamide) is worked into the teeth as well. These teeth can be round-shaped or have other forms, suitable to the respective gear wheels. At least one guide board on either side of the belt pulleys, prevents the timing belt from leaving the wheel over the side, rubbing against the engine housing, thus being worn down narrower and narrower, until, in the end it tears through.