When Should I Change My Cambelt — and What Happens If It Snaps?

The short answer

Change your cambelt (timing belt) at the interval your manufacturer sets — usually somewhere between 40,000 and 100,000 miles, or every four to ten years, whichever comes first. The time limit matters as much as the mileage: rubber belts age even when the car is not doing many miles. Your service book or handbook gives the exact figure for your engine, or we can look it up from your registration.

What a cambelt does

The cambelt keeps the crankshaft and camshafts turning in step, so the valves open and close at exactly the right moment as the pistons move up and down. It sits inside the engine behind covers, so you cannot usually see its condition without taking things apart — which is why it is changed on a schedule rather than when it looks worn.

What happens if it snaps?

The engine stops immediately. On many engines — known as interference engines — the pistons then hit the open valves, bending them and sometimes damaging the pistons and cylinder head. That can turn a planned belt change into a major engine repair or even a replacement engine. On other engines the belt snapping just leaves you stranded, but you cannot rely on that.

There is often little or no warning before a belt fails. A squeal or rattle from the front of the engine can point to a worn tensioner or pulley, and that should be checked straight away.

Belt or chain?

Some engines use a metal timing chain instead of a belt. Chains are designed to last much longer but can stretch, especially if oil changes have been missed. A rattle on a cold start is a common sign. Some newer engines use a wet belt that runs in the engine oil — these have their own intervals and are sensitive to the correct oil being used.

What we replace

We replace the belt along with the tensioner and idler pulleys, and on many engines the water pump as well, because it is driven by the belt and sits behind the same covers. Doing it all at once avoids paying for the same labour twice later on. If you have bought a car and do not know whether the belt has been done, assume it has not — call us on 0121 476 2287 with your registration and we will tell you what is due.