Q. What is a timing belt or cam belt?
My repairer has recommended that my timing belt (or cam belt) is due for replacement.
In more ways than one, a question of timing...
There’s nothing quite like the ‘clatter-bang-crash’ sound of pistons and valves arguing with each other when they have had a close encounter of the 1st kind! This is soon followed by the imagery of $$$ symbols running through your mind as the vehicle grinds to a halt. Total exasperation follows when the worst fears are realised and confirmed by the AANT Patrolman that the timing belt (or cam belt) has broken.
Let's get an understanding of what the timing belt actually does. The belt is located at the front of the engine and is driven by the crankshaft, which in turn drives the cam shaft, usually in a clockwise direction. On a front wheel drive vehicle, the belt will be facing the side of the engine bay, where access for replacement may be tight. The belt will be completely covered up, making assessment of condition impossible without some dismantling of covers, pulleys and ancillary belts.
The crankshaft and the camshaft need to rotate in unison at precisely the right time to allow the induction of the air and fuel mixture, compression of the mixture, combustion of the mixture and finally, exhausting the burnt mixture. The crankshaft is responsible for the pistons and their up and down movement, the camshaft is responsible for the valves opening and closing, allowing the engine to “breath”. If the timing of these components is not correct, it can allow the moving parts to be in the same place at the same time, big problem!
So why use a rubber belt for such an important task I hear you say! Rubber belts are quiet in operation and allow a more compact engine design for smaller congested engine bays. Being used extensively through out the 80’s and 90’s, manufacturers have realised the problems that timing belt maintenance, or lack of, is effecting the reliability rating of their products. Due to vast improvements in quality and durability, a lot of manufactures are going back to the good old-fashioned chain drive whereby there is no replacement interval or maintenance required. This equates to chain drive engines having significantly reduced servicing costs.
The manufacturer of the vehicle specifies a replacement time for the belt because “prevention is better than the cure”. A very common replacement interval is 100,000k or 5 years, which ever occurs first, but here in lies the problem. The vehicle maybe 10 years old but may have an unusually low kilometre reading, say 75,000k for example. The owner of the vehicle assumes that because it has only done 75,000k the belt must still be ok. It must be remembered that the timing belt is made of rubber, and like all rubber, there is a shelf life that must be considered. Rubber can age, crack and perish over time, so technically the belt in this vehicle is way overdue for replacement, hence, in more ways than one, “a question of timing”.
It is also very important to check to see if the manufacturer has changed or brought forward the replacement interval for the timing belt. For example, some Alfa Romeo models were originally specified for timing belt replacement at 120,000k, this has been revised to 60,000k or 3 years. Another good example is the Holden Astra whereby the belt replacement was changed to 60,000k instead of 120,000k as originally specified. Holden only notified it’s customers visiting their dealer network so it is quite possible that there are many owners out there unaware of the changes in specification. For any vehicle fitted with a timing belt it is good practice to make yourself fully aware of the current specifications for your particular model.
If you are having your timing belt replaced you may receive a call from your repairer suggesting other components such as idler pulleys, tentioners, water pump, crankshaft and camshaft seals, ancillary drive belts etc. require further scrutiny or replacement. These are very good recommendations as it will be the opportune time to look at these things whilst this area of the engine is dismantled. After the job is done, it’s a good idea to keep all of the paper work. It will provide good proof and service history should you wish to sell the vehicle at some point in time. More often than not, your potential buyers will ask the question “have you changed the timing belt?” You will then be in the best position to answer their “question of timing”.