Car timing belt: how to check your cambelt
A car's timing belt, also known as the cambelt, is a crucial part of your engine. Our expert guide will help DIY mechanics feel less intimidated as you look to service or repair your car.
What is a car engine timing belt?
The timing belt is a simple strip of rubber and metal that makes sure that the engine's key moving parts are choreographed to millisecond accuracy.
Without your cambelt, metal is likely to smash 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 because almost all engines in recent history are of the interference type, the risks are great. An interference engine is one in which the internal spaces are filled with different parts at different times in the ignition cycle. If they all fill up the space at once, game over.
Cambelt or timing belt?
A timing belt and a cambelt are the same thing, so there's no difference. Some engines have a chain instead of a belt and in this instance it tends to be known as the timing chain.
A drivebelt, or to give it its full name: an auxiliary drivebelt or serpentine belt, is different. This is used to drive ancillary equipment such as the power steering, alternator, air-con etc. If this snaps the engine won't be damaged, although you won't be able to drive much farther with the alternator out of action.
Car timing belt: when to change?
Your Haynes Manual will tell you when your engine's timing belt needs to be changed. If you can't find a Manual for your car there's a good chance that AutoFix – another Haynes product – will have the information. You'll find this under the Service Intervals heading.
A cambelt's change interval is always shown as a number of years and miles. For example, the Citroen C4 Spacetourer with the 1.2 Puretech petrol engine has a timing belt interval of 62,500 miles/72 months.
Whatever your car's cambelt/timing belt interval is, it's important to change it as soon as you reach either of those numbers. So in the case of the Citroen above, if you get to six years but have only covered 40,000 miles, you need to change the belt now. And if you've covered 62,500 miles in four years you also need to change the timing belt.
Timing belt or timing chain: what does my car have?
You've probably asked yourself this question when you're buying a used car, and you're wondering if the service history shows that the cambelt has been changed.
If it hasn't, the car may not have reached the set interval. But there's also a chance that the vehicle has a timing chain instead of a belt. You'll find this information in chapter 1 of your Haynes Manual or in the Maintenance & repair > Engine section of AutoFix.
You'll have one thing less to worry about if your car has a timing chain, because chains don't need to be replaced at set intervals. They can still stretch over time, but they generally last a lot longer than belts.
Timing belt replacement cost UK
How much does it cost to change a car's timing belt? Get a garage to replace a timing belt and tensioner(s), and you're likely to be landed with a bill of at least £400, but it could be a lot more if the water pump needs to be changed at the same and the belt is hard to reach.
That's because there's a lot of labour involved to replace a timing belt. The belt itself can cost as little as £20, but the job of getting to it and changing it can take several hours. This is why Haynes can save you so much money by helping you to do it yourself.
How do I check my timing belt?
Even if your car's timing belt interval is still some way off, it's worth inspecting the cambelt's condition and operation, if possible. A few minutes spent nosing about in the engine bay could save you thousands if you spot something amiss.
Take the cover off
Your Haynes Manual will show you how to do this. With it removed, 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 the belt
With the engine running and the timing belt cover off, look at the belt as it runs. 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.
How do I change my car’s timing belt?
A competent home mechanic can change a cambelt with a Haynes Manual to hand.
Every car is different, but there are some things you should avoid universally, as well as some important ‘best practice’ things, too.
Lock the cam or cams. This is especially important on twin-cam engines (as shown below), 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.
Change the belt tensioner(s)
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.
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.
Put it in neutral!
Don't leave the car in gear. If you do, and the car moves a little, 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.
Make your mark
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.
If in doubt…
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 our 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.