If you hear a rattle or slap from inside the engine
Avoid driving the car. A rattling or slapping noise from within the engine can be a timing problem, and the UK's GEM Motoring Assist says not to drive on it. If it starts on the road, pull over somewhere safe and switch off. If the engine has stopped suddenly and won't restart, don't keep cranking it. Call roadside assistance and have it towed to a mechanic. If you're stuck near traffic, get everyone away from the road, and if anyone is hurt or in danger, call 000.
Belt and chain, side by side
| Timing belt | Timing chain | |
|---|---|---|
| What it is | A toothed belt, usually rubber | A metal roller chain |
| Where it runs | Usually outside the engine behind a cover. Some newer engines run a wet belt in the oil | Inside the engine, in the oil |
| Is it scheduled? | Yes, by the maker, by time and distance | Usually not, because it's intended to last |
| How it warns you | It usually doesn't | A rattle at idle, most of all just after a cold start |
| What shortens its life | Age, distance, and oil or debris on the belt | Wrong oil, late oil changes, worn tensioners or guides |
What is a timing belt?
The crankshaft is turned by the pistons. The camshaft opens and closes the valves. The timing belt, also called a cambelt, connects the two so they stay exactly in step.
Metal chains have become more widespread in car engines built since the 1990s, partly because they drop the regular belt replacement. Plenty of belts remain, though. Since 2008 some engines have used a wet belt, which runs in engine oil, so a belt doesn't always mean an older design.
When to replace a timing belt
Go by your maker's schedule, on both time and distance. GEM says to change the belt at whichever comes first, and sooner if the car mostly does low-speed city driving.
The intervals vary more than most people expect. The RACV says a major component like this could fall at 60,000 km, 105,000 km or 180,000 km. NRMA's used car review of the four-cylinder 1995 to 1998 Suzuki Vitara says to check the belt was replaced every 100,000 km. One current Kia diesel has the mechanic inspect the belt every 120,000 km and replace the whole system every 240,000 km.
That Kia manual shows why you can't go by the badge. Its timing belt line applies to the diesel only, even though the same manual covers a petrol engine too.
Why a broken belt is such a big job
A belt that lets go stops the engine straight away, and GEM says belts tend to give very little notice. On many modern cars the damage goes further. They use interference engines, where the valves and pistons share the same space at different moments. Lose the timing and the valves can hit the pistons.
So the planned replacement is the small job, and the failure is the big one. That's the reason a mechanic will press you about a belt that's overdue, even though the car feels perfectly fine.
Do timing chains ever need replacing?
They're not supposed to, but sometimes they do. RAA says chains don't wear and should remain intact for the life of the vehicle. GEM says they're intended to last the life of the engine, and that this isn't always the case.
Oil is usually the difference. A chain lives in engine oil, so the wrong oil or late oil changes hurt it, and poor lubrication or a failed tensioner can cause early wear. Keep to the oil schedule in your engine oil guide and a chain has every chance of doing its job.
The warning signs are a rattle at idle, misfires, or an engine warning light. Don't wait on any of those.
How to find out which one your car has
Read the service schedule
If the logbook has a timing belt line with a distance and time, it's a belt. If there's no line at all, it's probably a chain. Confirm it with a mechanic.
Check the exact engine
One model can come with different engines, and they don't always share the same setup. Use the engine in your car, not the model name.
Look through the service history
A replacement should show up in the stamps or on an invoice, with the odometer reading.
Ask a mechanic who knows the make
Give them the year, the model and the rego. They can usually tell you in a minute.
What a good timing belt estimate covers
- The belt, and whether it's a full kit.
- The tensioner and idler pulleys. Kia's schedule replaces these with the belt.
- The water pump, if it's driven by the belt. Replacing it at the same time is often recommended.
- Any drive belts that come off to reach it.
- A logbook stamp and an invoice showing the odometer reading.
What you can do, and what to leave
You can
- Find out if your engine has a belt or a chain.
- Write the next belt date and odometer reading in your phone.
- Keep every invoice that mentions a timing belt. A buyer will want to see it.
- Listen for a rattle in the first few seconds after a cold start.
Leave to the mechanic
- Checking and replacing the belt. RAA says only a mechanic can do this.
- Any work behind the timing cover.
- Testing a suspected chain or tensioner problem.
- Reading fault codes linked to engine timing.
If it were our car
We'd find out which one it has this week. If it's a belt, we'd write down when the next one falls due and treat that date as firm, even if the car feels fine. If it's a used car with no record of a belt change, we'd follow RAA's advice and replace it, because not knowing is the bigger risk. If it's a chain, we'd keep up the oil changes and take any new rattle straight to a mechanic.
Who should do the job?
A timing belt is a precise job, and on some engines it's a long one. Choose a mechanic who's done that engine before and has the right locking tools, because getting it a tooth out can do real damage. European cars, late-model diesels and wet belts deserve someone who sees them regularly.
Tell us the job, and the engine if you know it. A local mechanic who specialises in your car.