Timing belt

Template:Reqimage A 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 use timing gears.

It connects the crankshaft to the camshaft(s) which in turn controls the opening and closing of the engine's valves. In a four-stroke engine requires that the valves open and close once every other turn of the crankshaft. The timing belt does this. It has custom teeth to turn the camshaft(s) synchronized with the crankshaft and is specifically designed for a particular engine. In some engine designs, the timing belt may also be used to drive other engine components such as the water pump and oil pump.

A gearing system can be used to connect the crankshaft to the camshaft at the correct timing. However gears and shafts constrain the relative location of the crankshaft and camshafts. A belt or chain allows much more flexibility in the relative locations of the crankshaft and camshafts. Furthermore, belts are cheaper than a gearing system. While chains may be more robust, rubber belts are quieter. A timing belt is a specific application of a synchronous belt used to transmit rotational power synchronously.

Timing belts are typically inaccessible and difficult to inspect. Replacement at specific intervals is recommended by the manufacturer. The manufacturer may also recommend the replacement of other parts, such as the water pump, when the timing belt is replaced because the additional cost to replace the water pump is negligible compared to the cost of accessing the timing belt. Failure of the timing belt will leave the engine non-functioning. Depending on the design of the engine, the piston and valve paths may "interfere" with one another and incorrect timing in their movements may result in the piston and valves colliding. (Such designs are also called "interference head" or "interference engines". Conversely, non-interfering engines are called "free-wheeling".)

In interference designs, regular service is especially important as incorrect timing may result in the pistons and valves colliding and causing extensive engine damage. The piston will likely bend the valves or if a piece of valve or piston is broken off within the cylinder, the broken piece will cause severe damage within the cylinder. In some newer engines, timing belts are designed to last the effective life of the engine. When a timing belt is replaced, care must be taken to ensure that the valve and piston movements are correctly synchronized.

A timing belt is typically rubber with high-tensile fibers (e.g. fiberglass[1] (http://www.aa1car.com/library/ar594.htm) or Kevlar[2] (http://www.machv.com/ketibe.html)) running the length of the belt. Rubber degrades with higher temperatures and with contact with motor oil and antifreeze. Thus 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). Older belts have trapezoid shaped teeth. Newer manufacturing techniques allow for curved teeth that are quieter and last longer.

Aftermarket timing belts may be used to alter the engine performance[3] (http://www.conceptzperformance.com/Cart/description.php?II=356&Car_Type=NIS300&UID=).

The first known timing belt was used in 1945[4] (http://www.advanceautoparts.com/english/youcan/html/ccr/ccr20020301tb.html). The German Goggomobile microcar was the first mass produced vehicle to use a timing belt[5] (http://www.motorminute.com/Service/TimingBelts.pdf) in 1950. The first American vehicle to use a timing belt was the 1966 Pontiac Tempest.

External links

• List (http://www.motorminute.com/Service/TimingBelts.pdf) of interference engines and recommended timing belt replacement intervals