The safety margin of the manufacturer’s “precautionary” change for a timing belt mileage is very large indeed and it assumes even severe usage.
Question: My car manual says I should change the timing belt every 100,000 km. My garage says I should buy not only a new belt but also a complete timing belt “kit”, including the tensioner bearing, its mounting and its shaft (altogether nearly five times the cost of the belt itself). Why is a tensioner bearing so much more expensive than other bearings of similar size, and is all this necessary in the first place? I have now done 120,000 km and there is no sign of anything wrong with the timing.
Answer: All manufacturers recommend a timing belt change (many at 100,000 km) as a purely “precautionary” measure.
Not because the belt will be faulty or fragile after that mileage, but because timing belt failure can cause so much (and such expensive) damage to the engine. It is an emphatic example of “better safe than sorry” and “prevention being better than cure”.
Should you change the timing belt every 100,000 km?
The timing belt ensures perfect coordination of many different parts of the engine, so even when they are each moving up and down or round and round amongst each other –thousands of times per minute and with considerable force - each one is in the right place and doing exactly the right thing at a precise nanosecond.
Modern timing belts are extremely robust, and their length and toothed inner surface are very precise. If they stretch over time or if their teeth are distorted, things can get fractionally out of step, and engine performance will suffer.
If the belt breaks, there is no coordination whatsoever, and different parts that should never meet start to bump into each other like jackhammer tips. The damage can be instant and severe. Parts of the engine can smash each other to pieces.
So rather than wait for belt failure to progress from unlikely to possible to probable and then almost certain, it makes sense to change the belt before there is any sign of a timing problem.
The price of a new belt, and the cost of fitting it, can be several thousand shillings, but that is petty cash compared with the costs inflicted by a belt breaking.
The safety margin of the manufacturer’s “precautionary” change mileage is very large indeed and it assumes even severe usage. So for ordinary motoring, it is just a guideline, not an urgent deadline. How far you might exceed that guideline is up to your risk management.
Car owners with a strong safety-first approach might go even further and change not only the belt but also its tensioner bearing and the bearing’s mounting and shaft.
They too suffer some wear and if they wobble or seize they can break even a new belt. Workshops are only too happy to recommend what they call a whole timing belt “kit” which can increase the cost from several thousand to tens of thousands.
While the “kit” option is safe advice, it is unlikely to be necessary at the first belt change, and might not be essential at the second (200,000 km). But the tensioner, cradle and shaft should at least be checked, and if there is any (!) sign of wear–play or a grating sound – then replacement is recommended.
