Your timing belt is responsible for keeping your engine's various components working together in synchronization. Because it is made of rubber, it will stretch and crack overtime. A slipped timing belt can cause engine misfiring and a completely severed timing belt can cause a complete engine breakdown. Just like all the other belts in your vehicle that provide power to other major systems like your ac compressor and your power steering pump, the upkeep of these belts is extremely vital to your vehicle's systems running safely and efficiently. http://www.goodwillrubber.net/automotive-rubber-parts/