Automotive timing belts generally are made of rubber, o […]
Automotive timing belts generally are made of rubber, often with fiberglass or Kevlar woven into them for extra strength. They are known to be very quiet as they rotate, but they do wear out over time. Most vehicle manufacturers recommend that timing belts are changed between 60,000 and 100,000 miles, though there are exceptions, both higher and lower.
Timing belts frequently snake through a series of pulleys and have mechanical or self-contained hydraulic timing tensioners to keep the proper tension on the belt throughout the entire rpm range. These mechanical and hydraulic tensioners and pulleys should always be replaced at the same time as the belt. They are all the same age with the same mileage, so replacing them is a great habit and great insurance.
Along with pulleys and belt tensioners, water pumps are often replaced at the same time as timing belts. This is for two reasons. Some water pumps are actually driven by the timing belt itself, and are therefore a liability if they are old and worn out. The other reason is because many water pumps, especially on newer vehicles, are tucked behind the timing belt due to packaging constraints. You wouldn't want to replace the timing belt and then have to take it off again later when your old water pump fails. Doing the job twice is never fun.
A timing chain on the other hand looks just like a bicycle chain, but much cleaner. The beauty of the timing chain is that it typically lasts a very long time. Some car manufacturers recommend replacing it at certain mileage or time intervals, while others claim that the chain is good for the life of the automobile. It really depends on the make and model of the car or truck. The downfall of timing chains is that they are heavier, generally known to be noisier, and if they do break, it is usually catastrophic to all of the surrounding engine parts.
Much like automotive timing belts, timing chains have tensioners that keep the chain from flopping around. The difference is that timing chain tensioners are nearly always controlled with the engine oil pressure. As you can imagine, if the engine oil pressure becomes low for whatever reason, the oil-driven timing chain tensioners will lose pressure and the mechanical engine timing will offset. This will cause poor engine performance and give the chain an opportunity to fail in grand fashion. The other benefit to timing chains is that they rarely have anything to do with the water pump, so replacing them at the same time isn't nearly as necessary as it is with a Rubber Timing Belt. As with everything in life, there are exceptions to this rule. Luckily, your car probably isn't one of them.