In a piston engine, either a timing belt (also called a cambelt) or timing chain or set of timing gears is used to synchronize the rotation of the crankshaft and the camshaft. This synchronisation ensures that the engine's valves open and close at the correct times in relation to the position of the pistons. Design In most piston engines, the camshaft(s) are mechanically connected to the crankshaft. The crankshaft drives the camshaft (via a timing belt, timing chain or pushrods), which in turn actuates the intake and exhaust valves. These valves allow the engine to inhale air (or an air/fuel mixture) and exhale the exhaust gasses. The most common devices to transfer the drive are toothed rubber belts, metal timing chains or a set of gears. The teeth of the belt/chain/gears mesh with both the crankshaft and camshaft(s), thereby synchronising their motion. In many older overhead valve engines, the camshaft is located in the block near the crankshaft, therefore a simple gear system is often used to drive the camshaft. Overhead camshaft engines mostly use timing belts or timing chains, since these are better suited to transferring drive over larger distances. Timing chains were common on mass-production cars until the 1970s and 1980s, however since the 1990s timing chains have become more common due to the replacement intervals required when using timing belts. Toothed rubber belts The phrase "timing belt" usually refers to a rubber toothed belt. The advantages of timing belts are typically a lower cost, reduced friction losses, less noise and that belts traditionally do not require lubrication. The main disadvantage is that belts wear over time, therefore belt replacement is recommended at specific intervals. Replacement of the engine's water pump at the same time is often recommended, since the water pump is also subject to wear and easily accessed during the replacement of the timing belt. Timing belts are typically located in front of the engine and are often behind a cover for protection against dust and debris. However a few engines since 2008 have used "wet timing belts", whereby the belt is lubricated by engine oil to reduce friction. In some engine designs the timing belt may also be used to drive other components, such as the water pump and oil pump. Construction A timing belt is typically made from rubber, although some belts are instead made from polyurethane or neoprene. The structure of the belt