What Is A Cam Belt And When Do You Need To Change It?

What Is A Cam Belt And When Do You Need To Change It?

It’s hard to buy, own and maintain a car without hearing the terms cam belt,  timing chain, or timing Belt. Whether upon purchase, at a service interval, or worst of all, when something’s gone wrong! 

In this article, we’ll clear up any confusion about what cam belts are, what they do, how long they really last, how important they are, and what a replacement cam belt or chain can cost. 

Bumper knows a large repair bill on your car is the last thing you want to spend your money on, but essential parts such as cam belts are crucial for your safety. Learn how you can split the cost of repairs into monthly instalments, interest-free.  

What is a cambelt? 

Cam belts, or timing belts, are vital parts of a car’s engine, made of rubber, with metal wires embedded for strength. Typically, the belt will be mostly covered by plastic guards. The top half of an engine, or Head, houses the valves and camshafts. The latter components control the flow of fuel and gases in and out of the engine, and their rotation is critical to the engine running properly. 

What does the cambelt do? 

The cam belt or timing belt is responsible for the timing of the internal combustion engine. The camshaft determines the timing of the valves, which are powered by the cambelt, from the crankshaft. Small notches in the belt locate the cambelt to the shafts. This ensures the rotational position of the camshaft relative to the crankshaft.  

Is a timing belt the same as a cam belt? 

Yes, a cam belt is a type of timing belt, just like a cam chain is a type of timing chain. As with many car parts and features, people refer to the same components by various different names. 

What is a cam chain? 

A cam chain serves the exact same purpose as a cambelt but is constructed of metal, similar in shape to a bicycle chain. It is generally encased in a sealed, metal engine cover. Cam chains are typically run ‘wet’ meaning they operate in the oil, aiding lubrication and efficiency.

How long do timing belts last? 

Many manufacturers claim the chain will not need replacing for the life of the engine, or at least 200,000 miles. They do not usually, therefore, feature on any servicing schedules, this is one of the main benefits of cam chains; their longevity,

How often to change a timing belt? 

Cam belts are usually rated to last between 60,000-100,000 miles, or around 5-7 years depending on the manufacturer. The cam belt tensioner should be changed at the same time, as these keep the cam belt in contact with the pulleys. 

Does my car have a cam belt or a cam chain? 

All modern car engines have either a cam belt or a cam chain but it pays to check which your car has. This way you can ensure the appropriate maintenance is carried out to avoid expensive repairs. There are some tell-tale covers and parts to look out for under the bonnet, but without delving into each specific model, these are the safest ways to check: 

Consult the owner's manual, specifically the service interval section. This will tell you the required service intervals, and whether your car has a belt or chain.  

If this is not available, a quick call to your local dealer or specialist relevant to your car should be able to help, it would also be pertinent to get an estimate of the cost for replacement of the belt or chain in the future.

What causes a cambelt to break? 

There are a few different reasons for a cambelt to fail, this is because they interact with multiple components and are made of perishable material.  

Old Age 

One of the most common reasons for cam belts failing is neglect. Failing to replace your old rubber cam belt in line with the servicing guidelines for your car will result in the material perishing and breaking. 

Improper Installation 

When installing a new cam belt, care should be taken to follow the manufacturer's guidelines for belt alignment, tension and fitting direction. Any one of these issues could cause the belt to wear unevenly and excessively.  

Belt tensioner fault 

As discussed, the cam belt uses a tensioner to remain in proper contact with the timing gears. If the tensioner stops providing this tension, the timing gears will strip the teeth or even throw the belt from the pulleys.  

Both outcomes result in a severely damaged belt and potential damage to the engine. Tensioners should always be replaced when a new belt or water pump is fitted because the cost of the new part is much lesser than the consequences of a failed belt. 

Signs your cambelt needs replacing 

Cam belts do not generally give much warning of failure without visual inspection. Worn belts will not give an audible warning nor affect the performance of the vehicle.  

One instance between normal function and complete failure may be that the belt jumps on one or both of the pulleys. This can be caused by a failing tensioner and will result in poor running or a complete failure to start.  

The best method of ensuring cam belt longevity is to replace it on or before the recommended intervals, with a quality belt kit. 

Cam chain 

Cam chains are slightly different because the chain and sprockets are metal, if the tensioner becomes faulty, noise can be heard specifically on start-up. It will take the form of a metallic tick, clatter or rattle.  

One tip is to search online for videos of owners of your make model and engine type with the term ‘timing chain noise’. There will usually be multiple results of which you can use to identify a suspect noise coming from your own engine.  

If any noise is heard, it is recommended to have this checked as soon as possible, as full timing chain or belt failure can be catastrophic for your engine.  

How much does a cam chain cost to repair?  

The total cost for a cam chain replacement can range from £700-£1300. Typical labour times are in the 4-6 hour range including tensioning and setup and part costs can be upwards of £300 as the chains are high-precision parts. 

Although according to most manufacturers, Cam Chains should not require replacement or service for the lifetime of the engine, this is not always the case, however. 

Sometimes they may need repair work. Causes can be material failures such as chain stretching. Other common cam chain issues include failing tensioners, worn sprockets and poor lubrication.  

In many cases, any issue with the timing chain is best resolved by the complete removal and replacement of the chain and tensioner. 

This can be expensive, and can sometimes only be tackled by a specialist garage. This is because there are often special tools required to successfully remove and replace the chain correctly. 

Another consideration for cam chain replacement is that the engine oil will need to be replaced, as the cam chain is lubricated by the engine oil. This adds to the parts list; an oil filter and oil. 

How much does a cam belt cost to repair?  

The total cost range to repair a cam belt is between £300 and £700. Cam belts are typically simpler to change. Some manufacturers require special tooling, often for locking the engine whilst the belt is removed, and sometimes for correct tensioning. These tools are cheaper than those needed for cam chains.  

The belt itself is also considerably cheaper, with new parts often only costing around £130, including a new tensioner and belt. One caveat is that in many cases, the cambelt will also power the water pump, this means it makes the most sense to replace this at the same time, adding an extra £40-60 for most vehicles.  

Cam belts are generally easier to change, but will often still require the removal of ancillary components such as the engine mount, alternator and aforementioned water pump. This means labour hours can range from 2-4 hours. 

Cambelt and cam chain failure 

There are two different types of engines, interference and non-interference. This refers to the configuration of the engine, and how compact the packaging is, most modern engines fall under the ‘interference’ category, meaning if the belt breaks, the engine could be damaged. 

What happens when a timing belt breaks? 

In a non-interference engine, often found in older vehicles, the car will not start or run, this is because the engine’s valves will not be closing or opening to allow fuel in and exhaust gases out 

In a more modern car, the severity of the damage will depend on when the belt is to fail. 

When starting 

When starting the engine, the cam belt has to turn the entire engine in unison, including the camshafts and water pump. This can overload a damaged belt and cause it to break.  

If the engine has not started running, threes a possibility that the pistons will not hit the valves. This would be the best-case scenario for a broken cam belt. 

Whilst driving 

As the cambelt is under quite a lot of stress during operation, it’s possible that the belt could snap whilst driving at speed.  

This will cause the entire valvetrain to stop moving, depending on where in the engine cycle the belt breaks, the engine could lock up and cause the driver to lose control. In this instance, it’s best to take the car out of gear or shift to Neutral if automatic.  

In interference engines, upon timing chain or belt failure, the pistons can come into contact with the valves, this will usually cause significant damage to the engine. Specifically, the valvetrain, camshafts and head. In some cases, it can also damage the pistons irreparably.  

Both scenarios will cost thousands of pounds to repair. This is why it is imperative to keep up to date with service intervals, as well as monitor any new noises or symptoms.

What are the symptoms of a broken cam belt?

As we’ve discussed, the timing or cam belt connects the rotation of the crankshaft to the camshafts and therefore the position of the valves. This means a broken cambelt will have a significant impact on the engine.

Failure to start

Without the valves being opened and closed at the right time, the engine will not be able to run. The valve's closing creates a pressurised chamber for the fuel to ignite, meaning no fuel can ignite in the cylinders. 

In some cars, the engine will still attempt to start, meaning it may make some disconcerting sounds whilst it turns over, injects fuel and the spark plugs fire.

Many modern cars, though have a crank and camshaft sensor, which detects the speed of the respective shafts and ensures everything is in sync. If it's not - for instance when the cambelt is broken - the ECU will either cut the fuel supply, spark or power to the starter motor. 

How to diagnose a broken cambelt

As above, the engine will not fire if the cambelt is no longer driving the camshafts. If therefore the car has an adequate fuel supply, a strong spark and no hindrance to the air intake, it's a good chance the cambelt has broken.

Rough Running

If the cambelt has stretched, but not completely broken, the engine may still run. In this instance, the camshafts can be slightly out of sync to the rest of the engine, but still, allow the cylinder to be pressurised at nearly the right time. 

The engine will run very poorly, though with the likelihood of backfiring and smoke from the exhaust very high. An engine with a suspected cambelt failure should not be run.

How to maintain the life of your timing belt

As the cam chain runs in a sealed system using the engine's oil, the quality of the oil will affect the wear and efficiency of the chain. The best way to help prevent premature chain wear is to maintain regular oil changes and to use the correct grade of engine oil. 

Cam belt 

As the cam belt is in the open air, it is not susceptible to wear due to poor oil in the same way a cam chain is. For engine longevity though, it’s still recommended to change your oil regularly! 

The only way to prevent premature cambelt failure is to maintain regular changes in line with the manufacturer's service intervals. It is also important to replace the ancillary components that also interact with the cambelt; namely the water pump and belt tensioner.  

How Bumper can help 

Now we’ve discussed the ins and outs of cambelts and cam chains, take even more worry out of the automotive experience by spreading the servicing cost with Bumper, completely interest-free! 

To apply for a credit limit of up to £5,000 and see dependable garages and dealerships in your area you can split the cost at enter your registration and postcode on our website.

Related Posts