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Timing Belt Replacement

Learn when and how to perform timing belt replacement on an automobile.

Proper vehicle maintenance, including timing belt replacement, can improve fuel economy. [©Jupiter Images, 2009]
©Jupiter Images, 2009
Proper vehicle maintenance, including timing belt replacement, can improve fuel economy.

Being sure to take care of timing belt replacement at the intervals recommended by a car's manufacturer is an important step in automobile maintenance, especially as more people drive older cars.

What is a timing belt?

A timing belt is used in an internal combustion engine as a drive belt that is propelled by the camshaft that operates the timing gear that opens and shuts the valves in the cylinder heads.

What does that mean, exactly?

Familycar.com provides more detail about precisely how the timing belt works and why it is necessary to replace it periodically. The timing belt's function is to turn, or rotate, the car's crankshaft at twice the speed of the camshaft, maintaining precise alignment. Engines have anywhere from one to four camshafts, and the job of each one is to close and open the car's exhaust and intake valves as pistons move in the cylinders. If the valves do not open and close precisely as required by the movement of the pistons, the engine will not function properly.

Timing belts are used in both "interference" engines and "non-interference" engines, and the difference is significant. In interference engines, the valves and the pistons are located very close to each other. So if the belt slips even just a little bit, the piston will collide into an open valve. The result, as one may imagine, is considerable engine damage because pistons break and valves bend, requiring what is known commonly as the "valve job."

In non-interference engines, the valves and pistons are not located as close to one other. So if the belt slips a bit, the damage generally is not as great. In both interference and non-interference engines, however, a failed belt will cause the engine to shut down right away, regardless of how far away from home or a service center one may be.

By contrast, some cars use timing chains instead of timing belts. Timing chains do not require routine replacement, but they make the engine run somewhat louder than timing belts do.

When does a timing belt need to be replaced?

There are no symptoms when a timing belt begins to wear down. Because of their location on the engine and lack of visual clues, timing belts are impractical to inspect, which is why many experts advise car owners to simply change the timing belt at manufacturer-recommended intervals, which are typically around 60,000 miles, but can sometimes be more than 100,000 miles.

Because of the proximity of the water pump to the timing belt in most cars, and because so much of the labor required for the two replacement jobs is duplicative, mechanics may suggest that water pumps be replaced at the same time that timing belts are replaced.

And while the job is not inexpensive, it is much less costly than waiting for the timing belt to break.

At the very least, correct timing has an impact on fuel economy, engine performance and emissions. Those, in themselves, are good reasons to make sure proper maintenance is performed.

Aside from that, however, timing belt replacement, while not a frequent job, is just as important as regular oil changes, air filter replacement and other essential tasks to the lifespan of an automobile. And neglecting to do the job because of its difficulty, inconvenience or cost can add up to even more difficulty, inconvenience or cost down the road.

Costs to Change a Timing Belt

There are many variables in determining how much it will cost to change a timing belt, based mainly on the type of car and the hourly cost of labor, if one chooses to have the work done at a service center.

The cost of timing belt replacement can range from $250 to $750, or even higher, depending on the type of car and the hourly rate. The job takes an estimated two to six hours, again depending on the type of car being worked on and who is doing the work.

Timing Belt Replacement in an Auto Repair Shop

In order to help assess whether timing belts need to be replaced, mechanics may ask questions similar to these:

  • Was the car purchased new? If it was, the owner will generally know if the timing belt has been replaced
  • Was the car purchased used? If so, the owner may or may not know if the belt has been replaced
  • Does the vehicle have 60,000 miles or more
  • Has the timing belt ever been replaced? If the mileage indicates it is time to replace the belt, and the job has not yet been done, the mechanic may recommend doing so

Do-It-Yourself Timing Belt Replacement

For those with the patience, tools and mechanical aptitude, replacement of a timing belt can be done outside of a repair shop.

PopularMechanics.com walks step-by-step through the process for those inclined to replace a timing belt themselves.

The first step is spending time studying the entire process in a repair manual or make- and model-specific Web site before beginning the job. Generally speaking, a mechanic undertaking timing belt replacement will need to remove the motor mount on the passenger side of the car, which requires powertrain support. Access to the underside of the car is usually required, as well

Other important things to keep in mind, according to Popular Mechanics:

  • Be sure to know where the "timing marks" are on the engine, with "the No. 1 cylinder aligned at top dead center on the compression stroke"
  • If there is any shrouding in the wheel well, it will need to be removed in order to provide access to the crankshaft and the lower timing belt pulley
  • Using some white paint to mark the camshaft top dead center makes the job significantly easier
  • When attaching the new belt, route it around the largest diameter camshafts and crankshaft first, and then around the smallest diameters

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