The timing belt is your engine’s boss. This simple strip or rubber and metal makes sure your engine is a perfectly balanced dance, every move choreographed to millisecond accuracy.

Without your timing belt, metal will go smashing into other bits of metal, valves will bend, connecting rods will distort and flex, cams will grind and graunch and when the noise dies down and the dust settles, all you’ll be left with is scrap. In short, the health of your timing belt is paramount to your car’s ability to function.

There are of course exceptions. If you have a non-interference engine a snapped timing belt will be just that. A snapped belt.

But as almost all engines in recent history are in fact interference, the risks are great. An interference engine is one in which the internal spaced are filled with different parts at different times in the ignition cycle. If they all fill up the space at once, game over.

So, what can you do to check the health of your timing belt, and what tips should you be aware of when changing it? Worry not, as Haynes has you covered.

How to check the health of your car's timing belt

Timing Belt Health Check

Mileage

This one is simple. Your owner’s or Haynes manual will tell you when the timing belt should be changed. Some cars it might be every 40,000 miles, some could be as much as 120,000 miles. Whatever the number, the belt should be changed on or before that mileage is reached.

Age

Look at the information you find above. Your intervals for changing the belt will be xx-miles or xx years. It does not matter if your car has only done 20k in five years. If the interval is four years, you have to adhere to it, otherwise you’re driving a grenade. Timing belts deteriorate with age. Do not run an old belt just because your mileage is low. The intervals or mileage or year, whatever comes first.

Take the cover off

If you take the timing belt cover off, you’ll be able to perform a visual check on the belt. You’re looking for frayed edges or damage, perhaps worn teeth on the inside of the belt. If the rubber looks to be shiny or marbled, that’s another sign it’s getting old, along with signs of cracking within the rubber.

Flex

With the engine running and the timing belt cover off, look at the belt as it runs around. It should stay tight and straight, if it’s flexing, that’s bad news and means it is more likely to jump teeth, which will give your engine a bad day indeed.

Do's and Don'ts

Obviously, every car is different in terms of changing the timing belt, and with that in mind, you should consult your Haynes Manual for specific instructions. That said, there are some thing you should avoid universally, as well as dome important ‘best practice’ things, too.

Do

Lock the cam or cams. This is especially important on twin-cam engines, but even on single cam engines it’s a good move. You may need to buy a model-specific locking tool, but it’s money well spent. You do not want the engine internals to move while changing the belt, or it’ll throw everything out of whack. If you lock the cams, that’s half the battle.

Don’t

When you change the timing belt, you must change the tensioners, too. If you’re going all that way to change the belt, putting a new tensioner or tensioners on is no work at all. Even if they sound and feel okay, change them. The same goes for the water pump if it’d driven by the timing belt. It just makes sense. Change the pump because you’re doing the belt, not the belt in three months because you forgot to do the pump.

Do

Buy a decent quality belt kit. There are plenty of cheap options online, but as the old adage goes: buy cheap, buy twice. This is a crucial part of your engine. Don’t be a cheapskate.

Don’t

Leave the car in gear. If you do, and you rock the car or move the car, you’re going to rock the gearbox, which will rock the crank, which will rock the engine internals and boom, everything is out of whack.

Do

Use marks. Use some white paint, or a marker, whatever you have to hand, and mark up where the cam sprockets are before you take the old belt off. That way, when the new belt goes on you have a reference point. If the markers don’t line up, you know something is awry. Frustrating, but better to find out this way than by starting the engine…

Don’t

Be afraid to ask a garage. We all like working on our own cars, it’s fun and for many, it’s therapeutic. However, there is no harm in asking a garage, either to do the job completely or for advice on what you’re doing. Knowledge is power, which is why we make out manuals. The more you have in your noggin, the better off you’ll be. But even with all the information to hand, you don’t have to do it yourself. It’s a big job, and one for seasoned home mechanics.