Wet belt vs timing belt vs chain: what’s the difference?

Wet belt, timing belt, cambelt, timing chain. They all do the same basic job, but they are built differently and they age differently. Knowing which one your engine has tells you a lot about what it will cost to look after.

What they all do

An engine’s valves have to open and close in exact time with the pistons. The crankshaft drives the camshafts to keep everything in step, and that drive is either a toothed belt or a chain. If it slips or breaks, the timing is lost, and on most modern engines the valves and pistons collide.

Conventional timing belt (cambelt)

A toothed rubber belt on the outside of the engine, behind a cover, running dry. It is quiet and cheap to make, but it has a fixed life and must be replaced on schedule, typically every five to ten years depending on the engine. The job is usually straightforward because the belt is easy to reach.

Wet belt

A toothed belt made from oil-resistant rubber that runs inside the engine, bathed in oil. Manufacturers use it because it is quieter and has less friction than a chain or a dry belt, which helps economy and emissions. The downside is that the oil gradually breaks the rubber down, and when it does, the debris goes straight into the oil system. Replacing it means opening up the engine and cleaning out the oil pickup, so it is a bigger job than a dry cambelt. See what a wet belt change involves.

Timing chain

A metal chain, also running in oil. Chains are designed to last much longer and many never need replacing, but they are not fit and forget. They depend on clean oil at the right specification, and a neglected chain can stretch, rattle and eventually jump a tooth. Replacing a worn chain is often an expensive job.

Side by side

Which does my car have?

Your handbook or service schedule will usually say, but the quickest way is our wet belt checker, or browse the list of wet belt engines. Or send us your registration and we will tell you.