What is a Timing Belt, and What Does It Do?

The timing belt is an integral part of your vehicle’s engine, keeping many of the moving parts operating together with precise timing, to produce optimum efficiency and power. A bad timing belt can cause catastrophic engine failure, so it’s important to stay on top of any required maintenance in that area and have the belt replaced according to the service interval set out in your vehicle’s owner’s manual.

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What Is the Purpose of a Timing Belt?

Your timing belt coordinates the combustion cycle of the engine by connecting the crankshaft and the camshaft. The crankshaft rotates with the movement of the pistons and the camshaft controls the movement of the intake and exhaust valves.

Each cylinder has intake valves that open to allow air and fuel into the combustion chamber. Once the proper amount of air and fuel has entered the chamber, the camshaft closes the valves and the piston moves up in the cylinder, compressing the fuel/air mixture. The spark plug then ignites the mixture and it explodes, forcing the piston to move to back down the cylinder and rotating the crankshaft. At that point, the camshaft causes the exhaust valve to open, allowing the exhaust gases produced in the explosion to exit the cylinder, and the process starts over again.

All the valves and the piston need to move in a carefully coordinated dance for the process to work effectively, without blowing up the engine. The rotation of the crankshaft is transmitted through the timing belt to move the camshaft.

What a Timing Belt is Made Of

Modern timing belts are constructed of rubber, synthetic rubbers like neoprene, polyurethane, or highly saturated nitrile, with high-tensile strength reinforcing cords made of Kevlar, polyester, or fibreglass. The reinforcing cords will run the length of the belt, to reduce the tendency of the belt to stretch out over time. Timing belts have trapezoidal or curvilinear teeth cut into one of the sides and these teeth are specially shaped and sized to connect properly with the pulleys on the crankshaft and the camshaft.  

Engines with timing chains will have oil flowing over the chain to lubricate and protect the parts. Oil can damage rubber, so engines with rubber timing belts will typically be constructed in a “dry” setup, where oil or coolant does not interact with the belt.

What Problems Does a Bad Timing Belt Cause?

Most modern engines are assembled so that the valves and the pistons occupy the same area in the cylinder during different parts of the combustion cycle. They are called interference engines. While this might seem like a bad idea because it could lead to the two parts colliding, it’s actually done in the name of efficiency and power, because the reduced volume of the cylinder allows for higher compression.

Older vehicles that used non-interference engines could often survive a broken timing belt without too much damage, but that’s not the case for modern interference engines. Because the valves and the pistons in modern engines need to share the same space in the cylinder, if the timing belt breaks, it will cause the camshaft to stop opening the valves in proper sequence and the pistons can collide with them, causing major damage to the engine.

If this happens, the cost to repair the engine can often be extensive, or even prohibitive, causing an owner to either replace the engine or purchase a new vehicle altogether.

How Long a Timing Belt Lasts

Many experts will suggest that a timing belt should be replaced after 60,000 to 100,000 miles of driving, or seven to 10 years of service. The best bet for any vehicle owner, though, is to follow the recommendations of the manufacturer. Every vehicle manufacturer will lay out a service interval for the timing belt in the service manual of the vehicle, and it is essential to follow that interval to avoid a costly and inconvenient timing belt failure.

Can I Drive with a Bad Timing Belt?

 If you are aware that you have an issue with your timing belt, you should have it replaced immediately. If your timing belt fails while you are driving, it could cause so much engine damage that it would require either a major rebuild of the engine or an outright engine replacement. While there are many vehicle maintenance tasks that can be deferred, a timing belt replacement is not one of them.

How Much Does It Cost to Replace a Timing Belt?

The cost of a timing belt can be quite low, but the labor involved in a timing belt replacement can add up. The timing belt is an internal engine part that requires the mechanic to remove multiple external engine parts in order to access and replace it. Depending on the make and model of vehicle, the cost of a timing belt replacement will start in the several hundred dollars range and can move into four figures.

The alternative though is a gamble because if your timing belt fails while driving, the repair costs will be double, triple or more in the end.

Should I Replace Other Parts at the Same Time?

The timing system in most vehicles with a timing belt includes the crankshaft and camshaft pulleys, a tensioner pulley, and often some idler pulleys. When replacing your timing belt, it is prudent to check the condition of your crankshaft and camshaft pulleys for wear. You should also replace the tensioner pulley and any idler pulleys in the system because the cost of those parts and a small additional labor cost will be insignificant, compared to the cost and labor involved in the entire repair.

Many engines have a water pump that is driven by the timing belt, and it’s a good practice that while the belt is off and the engine is torn down, to replace the water pump as well. All of these parts can often be found in what’s referred to as a “timing belt kit” which will contain the belt, all necessary pulleys and tensioners that operate the belt, and many times the water pump as well.

Replacing a timing belt is a challenging project, but if you do decide to tackle it on your own, be sure to consult with shop manuals and seek out information from experts before you start. The position of the crankshaft and camshaft pulleys need to be very accurately maintained in order for the engine to function properly.

Whether you need Trustworthy Advice on selecting the right parts for the job or your car’s repair needs special tools to get it done, AutoZone can help. Visit online or in-store for the advice, parts, and equipment to successfully change your timing belt.

Timing belt replacement is a often a labor-intensive job, so if you need help, seek out our list of Preferred Shops in your area that can help!

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