ALT-1 When to Replace your Timing Belt
Your car's timing belt is one of those parts that has to be replaced before it fails. This is similar to the way aircraft mechanics replace parts prior to their full service lives because airplanes can't risk mechanical failures in mid-flight. In your car's case, a broken timing belt (or failed timing chain) can at best prevent your engine from running and at worst cause catastrophic damage to pistons and valves which are extremely costly to replace.
What does it do?
A timing belt or timing chain is a device that controls when your valves open and close according to the position of the crank shaft. This in turn allows the fuel/air mixture into the cylinders, seals them for combustion, and then subsequent exhaust gasses to be expelled. In the event of a timing belt failure, the valves would not open at the appropriate times. Best case, this would cause a loss of power and fuel mileage while increasing emissions; worst case, this could lead to damaged or destroyed pistons which would require a complete engine rebuild or replacement.
What are the costs?
The best scenario is that your timing belt is replaced just prior to failure thus maximizing its useful life (roughly $500). If the timing belt/chain does start to fail, the best you can hope for is reduced engine power. The worst case scenario could cause significant engine damage. If you have what is known as an interference-type engine, the valves and the piston occupy the same space inside the cylinder at different times. Since the timing belt/chain controls this timing, its failure could mean piston to valve contact which is almost certain to cause destruction and thus replacement of both pistons and valves. This can be an extremely costly repair and may require the entire engine to be replaced (could be upwards of the total value of your car).
Timing belt versus chain?
Many modern automobile engines use a timing belt to sequence valve opening intervals. A few years ago, timing chains were much more common. Both perform the same task with timing belts being lighter and cheaper while timing chains tend to last slightly longer. The decision of which to equip a car's engine with is made by the manufacturer, this is not a choice a consumer makes when buying a car.
When to replace?
To maximize the useful life of your timing belt/chain it is best to replace at the manufacturers suggested intervals. As a rule of thumb, this will generally be between 50,000 - 100,000 miles. Since this can be such a vast difference in mileage, it is best to adhere to owner's manual recommendations. The engine manufacturer has done the mean-time-between-failure analysis and should have determined the maximum life expectancy with sufficient statistical certainty to be able to advise when to replace.
In summary, the money spent to replace a working component inside your car's engine can be a frustrating expense. However, the long term cost savings can be well worth the effort. Trust the manufacturer's recommendation and replace your timing belt along with any other suggested components at the proper service intervals. You will not only save more money in the long run, but will be a safer motorist along the way.
