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How long should a timing belt last and what happens if it breaks?

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Updated 9 Oct 2019Jonathan Nash
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The simple answer is a timing belt should last 90,000km or more, and it can be an expensive disaster if it fails!

So what is it?

A timing belt is literally that – an exceptionally strong, toothed, belt that is located next to the engine and is designed to keep the crankshaft and the camshaft properly synchronised, or ‘timed’.

Hang on a minute, I hear you say, what’s a camshaft and a crankshaft?

Well you can find out more about these components on AutoGuru’s crankshaft and camshaft pages but, put simply, the crankshaft uses the force of moving pistons to create the rotational energy to drive the car, while the camshaft controls the opening of the valves that let fuel in, and exhaust gases out, of the cylinder after the ignition process.

So why is the timing belt so important in this process?

Well, let’s take a closer look at what’s happening in the engine first.

At the top of each cylinder in an internal combustion engine are at least two valves.

One valve – the intake valve - lets in the combustible mix of fuel and air, while the other – the exhaust valve – removes the gases that are left after that ignition.

When the valves open and close is controlled by the camshaft.

Meanwhile, the piston that sits inside the cylinder and below the valves is forced into movement by the ignition of the fuel and air mixture.

Through its connecting rod, the piston turns the crankshaft.

Simple, right?

So, the process is:

  1. Fuel and air mixture comes in through the inlet valve and is ignited, with the explosive energy forcing the piston into a downward movement.
  2. The piston turns the crankshaft which, as it completes its rotation, moves the piston back up inside the cylinder.
  3. The exhaust valve is opened and the exhaust gases are expelled.
  4. As the piston begins moving back up the cylinder, the exhaust valve closes and the intake valve opens. The fuel and air mixture enters and the process starts again.

The important thing to note here is that when the valves are open, they move down into the cylinder and into a space that is also occupied by the piston at a different time in this cycle.

And this why the timing of all this movement is important and why the timing belt is so critical – it is connected to both the camshaft and crankshaft ensuring they are synchronised.

If something is off with the timing, however, and if the belt is in some way stretched or damaged or, indeed, completely broken, then the piston and valves may come into contact with each other.

And that spells disaster.

In the highly pressurised environment of the cylinder, where mini-explosions are taking place and components are moving at thousands of strokes per minute, the damage that can be caused is tremendous.

At the very least, the pistons will collide with and bend the valves, but these impacts can also damage the camshaft, the pistons themselves, the lining of the cylinder, seals and bearings . . . all in all, a pretty dire scenario.

And an expensive one too – repairing all this damage may get so expensive that replacing the entire engine may be a more viable option.

So, the best bet, as is always the case, is prevention.

Timing belts should last for more than 90,000km before needing replacement (check your service manual for how often your vehicle’s manufacturer recommends replacement), but getting your vehicle serviced on schedule should catch a failing timing belt before disaster strikes and give you the peace of mind that all is well.

A quick quote through AutoGuru will let you easily schedule and prepare for major services that include timing belt replacements.

Get instant quotes and transparent prices, it really is that easy!

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Written ByJonathan Nash

Jonathan has been writing about the auto industry for years and is particularly interested in the high-tech innovations sweeping the industry.

He’d love to own a Tesla Model S, but also adores anything with a V8 under the bonnet. 

He has yet to decide between an EV or a Mustang for his next ride.