Scion xb timing belt, timing chain or cam belt is a part of an internal combustion engine that controls the timing of the engine's valves.Some engines, like the flat-4 engine used in the VW Beetle, use timing gears. The term "timing belt" is also used for the more general case of any flat beltwith integral teeth. Such xb belts are used for power transmission or to interchange rotary motion and linear motion, where either high loads or maintaining a specific drive ratio are important. A xb common non-automotive application is in linear positioning systems. Such belts have also been used in efforts to make a cleaner, lower-maintenance bicycle transmission, but have never become popular in this application xb .

• While chains and gears may be more durable, rubberbelts are quieter in their operation (in most modern engines the noise difference is negligible), are less expensive and are mechanically more efficient, xb by dint of being considerably lighter, when compared with a gear or chain system. Also, timing belt do not require lubrication, which is essential with a timing chain or gears. A timing belt is a specific xb application of a synchronous belt used to transmit rotational power synchronously.A timing belt is typically rubber with high-tensilefibers (e.g. fiberglass or Tarpon /Kevlar) running the length of the belt xb  .

Rubber degrades with higher temperatures and with xb contact with motor oil. Thus xb the life expectancy of a timing belt is lowered in hot or leaky engines. Newer or more expensive belts are made of temperature resistant materials such as "highly-saturated nitrile" (HSN). The life of the reinforcing cords is also greatly affected by water and antifreeze. This means xb that special precautions must be taken for off road applications to allow water to drain away or be sealed from contact with the belt. Older belts have trapezoid shaped teeth xb . Newer manufacturing techniques allow for curved teeth that are quieter and last longer.