Find out what a cam belt is and when to replace it

The cam belt, or timing belt, is an essential component of your car’s engine. But what does it do, when does it need replacing and what happens if it breaks?

In this article

What is a cam belt?

Your car’s cam belt is a vital piece of the engine. The cam belt is made of of sturdy composites like Kevlar and polyurethane, with teeth on it that’s designed to keep the camshaft and crankshaft in time.

It’s also called a timing belt.

What does a cam belt do?

The main role of a cam belt or timing belt is to control the timing of your vehicle’s internal combustion engines. It controls the timing and sequence of when the valves to the cylinders open and close. To do that, it makes sure that the the crankshaft and the camshaft rotate in sync.

  • The engine’s camshaft controls the valves, letting fuel and air in and out.
  • The crankshaft moves the pistons up and down at the same time.
  • These 2 actions must be synchronised.
  • If the timing's off, the valves, pistons or other engine parts could get damaged.

Cam belts vs cam chains

The main difference between a cam or timing belt and a timing chain is the material. Unlike cam belts, timing chains are made of metal.

Timing chains are housed inside the engine and are lubricated by the engine oil, while cam belts are usually located outside the engine. But some manufacturers are now using “wet belts”, which like cam chains, run internally in the engine oil.

Cam chains tend to last longer as they’re made of a stronger material. Unless they’re “wet belts”, cam belts can dry out and crack over time if they’re not replaced. 

Does your car have a cam belt or a chain?

Whether your car has a timing belt or a timing chain depends on the make and model. For example, most BMW and Mercedes cars use cam chain engines.

Check you vehicle handbook to find out whether your car has a belt or a chain.

When to replace the cam belt

There’s no set rule for when to replace your cam belt. It depends on the make and model of your car, as well as how much you drive the car. It’ll usually need to be replaced more than once over the course of a vehicle’s lifetime.

Manufacturers will usually recommend to replace your timing belt after a set number of years or miles. This could be anywhere from 40,000 to 100,000 miles or 4+ years.

Check your vehicle handbook to see what your manufacturer recommends.

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Signs your cam belt needs replacing

Your cam belt might need replacing sooner than your vehicle manufacturer’s schedule recommends. There are a few tell-tale signs to look out for and things that can go wrong:

Noises from the engine

You should check out any unusual noises from the engine straight away. Cam belts don’t usually give much notice before they fail, but a rubbing sound from the belt cover area is a sign it’s about to fail. If you hear it, switch the engine off and call a mechanic to check it.

Car won’t start

If your car won’t start, it could mean there’s a problem with the cam belt. If the cam belt’s broken, then the cam shaft won’t rotate when the crankshaft turns, so the car may not start at all.

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Reasons for cam belt failure

One of the main reasons for cam belt failure is the auxiliary belt. If the aux belt deteriorates and shreds, the fibres get trapped under the cam belt as they both run off the crank shaft pulley. This usually causes the belt to jump or come off altogether.

On many cars, the cam belt also drives the water pump, so any issues with that can cause a failure too.

Cam belt wear and tear

The cam belt can wear out over the course of a car’s lifetime. On many cars, it can be tricky to get to the cam belt, so we always recommend taking your car to a mechanic if you’re not sure. Stick to your manufacturer’s servicing schedule for the best chance of spotting any problems. 

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What happens if the cam belt breaks?

It’s always better to get your cam belt checked with regular car servicing or to take it to a garage as soon as you notice a problem. If you leave it and the cam belt snaps completely, it’ll cause a much bigger problem.

  • If the cam belt snaps while you’re driving, it could be very dangerous. The engine could seize up, causing steering and brakes to fail.
  • The pistons can hit the valves in the cylinders, damaging the engine.
  • A non-interference or free-wheeling engine won’t suffer as much damage, but still might sustain some.

It’ll be much more expensive to fix if the timing belt snaps and causes other engine damage. So if you notice any unusual noises or a drop in engine performance when you’re driving, pull over in a safe place and tell us.

How much does a cam belt cost?

The price of a new cam belt or timing belt plus labour varies depending on the make and model of your vehicle. Prices for parts and labour can start from around £250 and go up to over £500, or even over £1,000 for some luxury vehicles.

When you get a quote, make sure it includes the price of the belt, tensioners and labour. In some cars, you have to take the timing belt off in order to get to the water pump. So if you need to change the cam belt, some people choose to have the water pump changed at the same time as the cam belt will already be off.

Published: 27 November 2020 | Updated: 27 November 2020 | Author: The AA

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