A timing is a rubber belt with teeth that keep the valves opening and closing at precisely the right time in relation to pistons. If the engine gets “out of time”, the pistons will hit an open valve and damage the engine.
Over time, the rubber on the timing belt degrades and the teeth fall off causing the the engine to go out of time. It is important to replace your belt long before that happens. Many cars use the timing belt to drive the water pump. Water pumps often fail around the same time as a typical timing belt interval so Harvey Road always replaces any timing belt driven components at the same time.
The cost of replacing your timing belt varies from car to car. The labor required to access the timing belt can be very intensive.