What Is A Timing Belt And When Should You Replace it?


If you’ve ever been told that your car needs a new timing belt, you’ve probably found yourself wondering: What Is A Timing Belt?

A Timing belt is a heavy duty, reinforced rubber belt that synchronizes the rotation of the crankshaft and the camshaft so that the engine’s valves open and close at the proper times during each cylinder’s intake and exhaust strokes.

What Is A Timing Belt?: The Long Answer

It’s a reinforced rubber band with teeth or notches on the inner side. It connects your engine’s crankshaft (which moves the pistons) to the camshaft(s) (which move the valves).

When you start your engine, the crankshaft is rotated by the starter until the engine is able to keep it spinning on it’s own. The internal combustion process is what makes that happen, and also what moves your car down the road. The rotation of the crankshaft moves the timing belt. The timing belt, in turn, moves the camshaft(s), which open the intake and exhaust valve(s). In a four-stroke engine (which is the type of engine found in most vehicles) there are four phases: the intake phase, compression phase, combustion phase, and exhaust phase.

On the intake phase, air and fuel are pulled into the cylinder by crankshaft rotation moving the piston downward. At this time, the camshaft rotation keeps the intake valve(s) open, and the exhaust valve(s) closed.

During the compression and combustion phases, the crankshaft’s rotation moves the piston upward. This upward movement is used to compress the air & fuel mixture so that it can be ignited by the spark plug. At this time, the camshaft’s rotation keeps all valves closed. Igniting this mixture causes an explosion, forcing that cylinder’s piston downward, which is how the crankshaft gets it’s rotation.

The final stage is the exhaust stroke. During this time, the crankshaft’s rotation moves the piston up and the camshaft’s rotation opens the exhaust valves. The remnants of the ignited air/fuel mixture are pushed through the exhaust ports and out your car’s exhaust pipe. Now the cylinder is empty so the next intake stroke can begin.

When Does My Timing Belt Need to Be Replaced?

As you’re driving down the road, the four-stroke process described above is repeating thousands of times per minute. Your timing belt is the conductor of this mechanical symphony! Timing belts aren’t one-trick ponies though. They also drive other components including the water pump, balance shaft, intermediate shaft, injection pump, and the oil pump. To work effectively, a timing belt must have a certain amount of tension controlled by the timing belt tensioner. In older cars, these tensioners would need periodic checking & adjustment (typically every few oil changes). Most modern vehicles are equipped with an automatic timing belt tensioner that does not require adjustment.

Over time, your timing belt will wear and stretch. Most timing belts are meant to last between 60,000 – 90,000 miles, so you should plan your vehicle’s maintenance schedule accordingly. It’s best to err on the side of sooner rather than waiting too long.

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