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The importance of changing the timing belt

By Hayden Featherstonhaugh

You may have heard the term ‘timing belt’ and that you need to change it periodically. You may have had your car’s timing belt replaced but do you know why? Do you know what it does?


Ok so you’ve heard something about this elusive timing belt.


Let me explain why we replace them and why they are important to the longevity of your car’s engine.


The timing belt is a toothed drive belt that connects the camshafts (top) of your engine to the crankshaft (the bottom) and synchronises their rotation.


As the crankshaft turns, it then pulls the timing belt to drive and turn the camshafts. As the camshafts turn they open and close small valves which allow the fuel/air mixture into the cylinder and the exhaust to escape once the combustion cycle is complete.

Click the link here to watch a short video from AGM Labs showing the camshaft and crankshaft in operation.

Main components of timing belt
The main components of a timing belt, crankshaft and camshaft.
Timing belt

The timing belt is made from various materials bonded together. These are a rubber compounds, a layer of nylon and a layer of a high modulus glass fibre cords. These layers provide the strength, flexibility and the heat resistance required.

As with many rubber components on your car’s engine, it will need replacing at a pre-determined interval set out by the manufacturer. Some manufacturers require the belt be replaced every three years regardless of kilometres travelled. Think of a Ferrari engine that is high revving and high performance. Other manufacturers will require replacement at three years or 90,000-100,000klm whichever comes first (Hyundai, Mitsubishi, early model Toyota, Mazda to mention a few). Finally some may not require a replacement until five years or 150,000klm whichever comes first (turbo diesel engines fitted to late model Toyota Hilux, Prado and Land cruiser are a few examples).


Timig belt layout

Ferrari F360 Engine showing twin timing belts and accessory belts

What is common is that they will all need to be replaced at the specified interval.

Why is this important?

As the components within the toothed belt, the guide and tensioner bearings age and wear they lose their ability to sustain the loads required to perform well. You can have many different failures within the timing belt and its components. Bearings that guide the belt will seize and cause excessive heat leading to belt failure. The belts can lose their teeth or snap.

If the synchronisation between the camshafts and crankshaft by way of a belt failure is lost the valves stop opening and closing and will stay open or closed depending on where in the cycle they were allowing piston and valve to collide with catastrophic consequences. At best, the engine may escape undamaged as evident in some Toyota engines. Most engines will hit valve to piston causing damage.

Here are a few examples of what can happen.

Timing belt bearing failure

Guide bearing has seized causing belt to melt and fail

Valve damage
Piston damage

Valve to piston impact causing broken valves, cylinder head and piston damage

Bent valve
New straight valve

Bent valves after impact and straight valves ready for installation into cylinder head

As you can see this is all quite catastrophic and results in an expensive repair.


Here at The Service Depot we specialise in timing belts and can determine when your belt is due, replace your timing belt and its components at the correct intervals using all new high-quality components from trusted brands like Dayco which offers a three year or 100,000klm warranty to give you piece of mind on all its timing belt kits.



Dayco Timig belt kit

The Service Depot

Unit 15 Eureka Centre, 29 Moreton Bay Road

Capalaba (07)3169 2333

Caring for your car.

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