Knowing when to replace your timing belt saves you from unexpected breakdowns and expensive repair costs.
The rule of thumb is, if you are not sure of the mileage covered on your timing belt then just replace it and start fresh from a known set-up.
Say it’s a car you just bought and the timing belt’s next replacement wasn’t indicated.
Just as its name suggests, a timing belt is part of an automotive engine synchronisation system that ensures the correct sequence between the crankshaft and the camshafts. In other words, it ensures that the engine runs without crushing the valves. If we were to give a basic example we would use a human mouth. You do not want to bite your tongue when eating food. So, the tongue has to keep turning food in your mouth but at the same time well secured that your teeth do not reach it.
The timing belt works in the same way. To ensure that it turns the valve away from pistons’ reach whenever the engine is running and at the same time keeps the engine timing marks correct at all engine speeds.
The timing belt is driven by pulleys, sprockets, idlers and tensioners. All these components are put together, and they make a timing kit.
Since all the above components are mechanically driven, they will wear out at some point and must be replaced.
Most car manufacturers recommend timing kit replacement every 100,000km. Sometimes the technicians carry out a serious mistake during replacement without knowing.
The service manual says “timing kit replacement”. This means all the components that drive the timing apart from the water pump. But many technicians will replace only the timing belt and then reuse the old pulleys, tensioners and idler gears.
This is just a time bomb because the older pulleys have just covered 100,000Km like the timing belt. Fitting a new belt on old pulleys has two disadvantages: –
- Reusing an old tensioner on a new belt risks belt jumping one or more teeth within the timing system due to a lack of sufficient tension from the tensioner due to worn out hydraulic seals or the spring.
- The idlers have ball bearings that are pre-greased from the factory and just like the timing belt, they are only perfectly functioning well below 100000km.
Once the 100,000Km mileage has been surpassed, the lubricant gets depleted, putting the bearings at a risk of sudden seizure which will cause the timing belt to snap instantly.
For these two reasons, it’s always good to replace the timing kit as a whole to avoid sudden engine failures resulting from the timing kit.
Different manufacturers have different technologies in engine production, especially the cylinder heads and the combustion chambers. In some cars, failure in the timing kit results in piston dents and valves bending which usually calls for a replacement of new parts before an engine can run again. This type of engine is known as the interference type, while in others when the belt snaps or jumps a tooth, the engine just shuts off without damaging anything and upon timing reset or a belt replacement, the car runs without any problems. This type of engine is called noninterference.
Causes of timing belt failure
Apart from the natural tear and wear of up to 100,000km as discussed earlier, sometimes other aspects can contribute to the premature breakdown of the timing kit.
Stones and pebbles
A worn out timing belt cover exposes the entire kit to foreign matters and more so stones. Once they get into the kit they jam it and can easily puncture the belt or make it jump a tooth which can cause problems.
Oil leakage could be a result of worn out seals probably from within the engine or sometimes it could be a sign of a worn-out timing tensioner. Any oil spillage is not good for the belt because it alters the coefficient of friction which can cause the belt to jump a tooth or more. Always replace worn-out seals within the timing cover.
High revs and overload
Excessive load and high engine revolution subject the belt to too much stretching. Sometimes sudden stretches result in elasticity which elongates the belt. At this point, it’s so easy for a tooth to be skipped or a belt to snap especially if it’s an old belt. Keeping low engine revs and unnecessary revs helps in attaining good mileage from the timing kit.
By Vincent Saleh