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Cam Belt Failure – What It Is & How It Happens

Collision damage aside, by far the most common reason our customers call us is down to engine damage caused by failure of the cam belt or timing chain. It usually means a car requires a new engine, or at least a top-end engine rebuild and in most cases the cost to do that is more than the value of the car itself.

Why are Cam Belts/Timing Chains So Important?

The engines in most cars are four stroke engines. As the pistons go up and down they suck in air and fuel, compress that mixture which ignites causing an explosion to shove the piston back down and on it’s way back up again it forces the burnt mixture out again.

In short, suck, squeeze, bang, blow, just like in the animation below but up to a hundred times faster!

4StrokeEngine_Ortho_3D_Small
Image credit: Zephyris, CC BY-SA 3.0, Link

Now with all that metal moving incredibly fast it’s vital that the valves at the top of the engine don’t come into contact with the pistons. This is where timing becomes crucial.
The belt with the arrow on the left hand side represents the cam belt or timing chain. Its job is to make sure that when the piston is heading rapidly upwards the valves remain closed or are only open just enough that the piston doesn’t touch them.

When a cam belt or timing chain fails this finely tuned system gets out of line. The moving parts of your engine are free to collide, causing catastrophic and usually terminal damage.

What can I do to make sure this doesn’t happen?

In short, regular scheduled maintenance. When manufacturers design and test engines they put a lifespan on different components with a decent safety margin built in.

If you look in the service handbook of your car it will tell you at what intervals the timing chain or cam belt should be renewed. This will be related to mileage but also time. Timing chains are obviously metal but cam belts are usually rubber and this perishes with time so even if your car doesn’t do many miles the cam belt will wear out.

Getting them changed on schedule can go a long way towards getting the maximum life out of your engine.

I Just Got a Quote to Change the Cam Belt – It Seems Really Expensive and Why Are They Quoting to Change the Water Pump Too?

The timing belt or chain on your engine doesn’t only control the opening and closing of the valves but also drives the pump that moves water around the engine to prevent it from overheating.

Like the belt the pump has a finite life and since neither component is particularly expensive it is best practice to change both at the same time. Swapping them out however takes skill and time so the bulk of the bill will be for the labor.

And a few hundred pounds for this job now is far better than a few thousand for a new engine or car!

I’m Thinking of Buying a Used Car – How Do I Know If The Cam Belt or Timing Chain Has Been Changed or Needs to Be Changed?

1. Do Your Research
The internet is your best friend. If you have a car in mind then type its make and model into Google followed by the words “known issues”. This will quickly supply you with a list of things to look out for when you start shopping. Or reasons why you should be considering an alternative choice entirely.

2. Be Sensible
Don’t fall into the “it won’t happen to me” trap. If an issue has happened to enough other people then it will happen to you.

3. History is Everything.
If the car you are looking at doesn’t have a stamped service book and tons of history then walk away. Cars are made in their thousands so even if you have a particular model, specification and colour in mind you can afford to be choosy. Take your time and find one that has a decent pedigree.

4. Drive a Hard Bargain
If you are buying from a dealer and you can’t see in the service history that the cam belt has been changed recently then make that a condition of your purchase. If you’re buying privately then be prepared to haggle hard and use the money off to get the job done yourself at the earliest opportunity.

What If a Belt or Chain Fails Prematurely?

There’s nothing you can do to prevent this but there are steps you can take to avoid being out of pocket.

It’s tempting in this kind of situation to go to an independent garage for a cheaper fix but that’s not always the case. Even if your car is out of warranty, if it is still relatively new and you are confident that it has been serviced and maintained as scheduled make sure you get the car recovered to a main dealer.

Manufacturers don’t like bad publicity. If it is obvious or you can demonstrate that premature component failure is to blame then the manufacturer may very well authorise a dealer repair at their expense. And even if they don’t cover the whole cost they may offer a goodwill contribution as a gesture of faith in an effort to retain you as a customer.

Of course if you are reading this after the fact then all of the above will be little consolation but it will hopefully go a long way towards ensuring that lightning doesn’t strike twice.

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