• It is important to replace a worn timing belt before it breaks.Auto Engine image by Andrew Breeden from Fotolia.com
  
  A timing belt winds around parts of a vehicle's engine to help keep the parts running properly and synchronously. The belt is typically made of synthetic rubber and reinforced high-tensile strength cords. The more a vehicle runs, the more use the belt undergoes, wearing it down over time. There are no sure-fire ways to detect a worn timing belt without physically looking at it, but paying attention to other clues can save a driver from a potentially serious break. Replacing a belt is a job best reserved for a professional mechanic or someone with considerable knowledge and equipment for fixing vehicles.
  
  

Glazed or Glossy Appearance

• One sign that a belt is becoming worn is a glazed or glossy appearance on the underside. This means the rubber is getting hard and will not provide the flexibility the belt needs. Another check is to press a fingernail or the tip of a screwdriver gently onto the belt. If the pressure does not leave a mark, it means the rubber is becoming too stiff. Some signs are much more obvious, like cracking or fraying. Belts with that kind of damage should be replaced immediately. The timing belt can be difficult to get to, so a visual and physical check is best done by a professional or car owner with experience in mechanics.
  
  

Noise

• Sometimes, a timing belt will produce a loud noise when the car is running, most often when the vehicle is first started and the engine is cold. The noise could be squealing, hissing, grinding, rattling, chirping or rumbling. Squealing is common for a loose belt, which can indicate wear and the need for replacement. If the belt is fairly new, yet is still making a noise, the driver should have the tension adjusted, but still visually check for unusual wear.
  
  

Vehicle Won't Start

• When a vehicle's engine will not start, it is possible the timing belt has broken. The engine will fail to start because without the belt, the camshaft will not rotate when the crankshaft turns. This can be diagnosed by watching the camshaft while turning the crankshaft. If the camshaft does not turn, the belt is broken.
  
  

High Mileage

• Vehicles have a typical life expectancy for timing belts. Different vehicles will have different expectancies. For example, Honda recommends replacing the belt after about 90,000 miles. Belt life expectancy should be stated in the driver's manual. Vehicle owners should follow these guidelines if no other problems arise before that.