When should you replace your timing belt?

If your vehicle uses a timing belt and you’re due for a replacement, don’t ever ask to see the old belt — it’ll look perfect, pristine, and as good as the new one that just went into your engine.

In fact, unless there was some external factor, such as an oil leak or a misaligned pulley, pretty much all timing belts will look fine at the time of replacement. It’ll likely leave you scratching your head, wondering why you just laid out all that coin to change it out.

A timing belt connects an engine’s camshaft, which controls valve action to the crankshaft, which then controls piston movement. It helps co-ordinate the movement of the engine’s valves and pistons so everything opens, closes, and moves up and down at precisely the right time.

Some manufacturers use a permanent metal chain instead of a belt; these don’t require scheduled replacements. But chain systems are physically heavier, use more fuel, and can exhibit an undesirable noise level in smaller vehicles.

To find out if your vehicle has a belt or a chain, consult the owner’s manual’s recommended service schedule to see if there’s a timing belt replacement suggestion, or contact your trusted shop. Replacing timing belts isn’t cheap; they often involve a substantial amount of labour to access the belt, and some automakers require new pulleys when their belts are changed. Bills can range from $400 to well over $1,000.

What’s the harm in stretching that interval, or ignoring it altogether? The answer, in one word, is clearance — or lack thereof. Many engines equipped with timing belts are classified as “zero-clearance,” which means if the timing belt breaks and the crankshaft rotates a few times before the engine stalls out completely, the valves will collide with the tops of the pistons. Ouch!

This usually means a few new valves at best, or a complete engine replacement at worst. And if you thought the cost of replacing the timing belt was high, you don’t want to see the estimate when it breaks. For engines that have clearance between the valves and pistons, when the belt breaks, the engine simply stalls and won’t restart.

Don’t bother asking your mechanic to simply inspect the belt and provide an opinion on how long you can drive it past its recommended replacement interval. Few good technicians will go out on that limb, knowing a possible engine replacement is riding on their answer.

Replacement intervals can range anywhere between 100,000 and 160,000 kilometres or more, depending on the automaker. Check your owner’s manual to find your vehicle’s interval and stick to it.