A timing belt is a very tough, rubbery strap that works to synchronise the motion of an engine’s camshaft and crankshaft.
The camshaft rotates and opens and closes the valves that allow the air and fuel mixture to enter the cylinders and this process must happen in sync with the movement of the crankshaft – the component that converts the movement of the pistons inside the cylinders into the rotational motion that is transferred to the transmission and ultimately to the wheels that move the vehicle. Should the ‘timing’ of the movement of the camshaft and crankshaft be incorrect then colossal damage to the engine can occur.
A timing chain does the exact same job as the timing belt but is a metallic roller chain. It is designed to have an extremely long lifespan and may never require replacement. However, as with a timing belt or any moving part, it can break or be damaged.
WHAT SORT OF DAMAGE CAN RESULT FROM A BROKEN TIMING BELT/CHAIN?
In short, catastrophic and extremely expensive to repair!
Inside an engine cylinder sits the piston which is forced downwards by the pressure of the combustion of a fuel and air mixture and back upwards by the movement of the crankshaft. At the top of the cylinder are the valves that open to allow the fuel and air mixture into the cylinder. In most engines, the open valves and pistons occupy part of the same space of the cylinder at different times. This means that if the timing of their movement is wrong, the pistons can smash into the valves. These components are moving extremely fast and the pressure and heat inside the cylinder is immense. Should things go wrong and they do make contact, the resulting damage can include bent valves, damage to the camshaft, damage to the cylinder head and cylinder wall, and potentially the piston too. It is a scenario that your car, and your wallet, most definitely want to avoid.
It is worth noting that engines in which a fully open valve extends into the space the piston also moves are known as an interference engines. Some models of cars have non-interference engines in which there is room for both to move without fear of contact.
SYMPTOMS OF A DAMAGED TIMING BELT/CHAIN
MISFIRE & ROUGH IDLING: The timing belt connects the crankshaft and camshaft via a series of pulleys and gears. The timing belt itself has ‘teeth’ that grip onto the gears. Over time, these ‘teeth’ will wear and begin to slip. This may cause one or more of the valves to open or close at the incorrect time, causing a misfire and rough idling.
The same symptoms occur when a timing belt loses its tension. A ‘stretched’ chain will loosen on its sprockets, affecting performance.
ENGINE WON’T START: If the timing belt/chain is broken, then the contact between crankshaft and camshaft is lost and the engine won’t be able to kick into life.
OIL LEAK: Timing belts are hidden from view by a timing belt cover that protects the engine from any debris kicked up when the car is moving. Over time, gaskets and seals in the engine may wear down and oil can leak into the timing belt area. This is not a good thing. The timing belt is designed to fit tightly in place and any fluid or lubricant that affects that grip is a cause for concern. Also, oil will impact the physical nature of the belt and make it wear and break down more quickly.
WHAT DOES IT COST TO REPLACE A TIMING BELT/CHAIN?
The timing belt is made from pretty robust material but will need changing at some point – perhaps at the 100,000km mark or so. As mentioned, a timing chain may never require changing.
Replacing either of these components is a complicated and time-consuming job, even for the most experienced mechanic, so the work will come at a price. However, if there is a problem, replacement is essential and is a job that can’t be ignored. You can expect the cost to be somewhere between $800 and $2000, possibly more depending on the vehicle and whether it is a belt or chain being replaced. That’s a hefty sum, but it should be remembered that ignoring timing belt/chain issues will result in calamitous damage to the engine, and the cost of repairing that damage will be much more severe.
As the timing belt/chain replacement is so labour intensive, it is not unusual for a workshop to suggest that other components, such as the water pump, be replaced while the mechanic has access to them. Given that a vehicle requiring a timing belt/chain replacement has probably racked up a fair few kilometres, it is likely that these ancillary parts are ‘tired’ too. Getting them changed at the same time as the timing belt/chain saves on the expense of having to go through the engine strip-down process again.
WANT TO LEARN MORE?
MTA Queensland’s Vehicle Maintenance course is designed for those who are interested in gaining valuable information and learning good practices for everyday vehicle use. The result: a safer journey with fewer breakdowns and repairs. If you have ever wanted to learn how to carry out preventative maintenance, then this course is for you.
17 April 2020
Please note the information contained on this page is general in nature and does not take into account your specific needs or circumstances. You should consider whether the information is appropriate to your needs, and where appropriate, seek professional advice.