Timing belt kit: when to replace it and why you shouldn't wait

What the timing drive does#

In an engine, the pistons move up and down and the valves open and close to let air in and exhaust gases out. The timing drive links the two movements, so the valves open at exactly the right moment relative to the pistons. The link is either a toothed belt or a chain, depending on the engine.

Because everything has to move in sync, a belt that jumps a tooth or snaps throws the whole engine out. That's why the timing belt isn't a part you replace "when it breaks", but before.

Belt or chain: how to tell which your car has#

You'll find out from the service book or the owner's manual, which lists a belt replacement interval if there is one. If you don't have the book, ask a garage: from the model, engine and VIN (the chassis number), the mechanic can tell you which drive it has and what interval the manufacturer recommends.

When to replace the timing belt kit#

The interval is set by the manufacturer for each engine and varies a lot from car to car, so don't go by what a friend had done on a different car. Some general rules:

• Kilometres or years, whichever comes first: the belt ages even when the car isn't used, so a low-mileage car still has it replaced after the number of years in the book.
• A used car with no proof: if no invoice shows when the timing belt was last changed, most mechanics will advise replacing it. That's cheaper than finding out on the road.
• A belt soaked in oil or coolant is replaced even before its interval, once the leak is fixed.
• Severe operating conditions, if the service book mentions them, can shorten the interval.

What's in a timing belt kit#

• The timing belt.
• The tensioner, which keeps the belt at the right tension.
• The idler pulleys the belt runs over. Their bearings wear along with it, and a seized pulley can break a brand-new belt.
• The water pump, on engines where the timing belt drives it. Because it's reached with the same labour, many garages advise changing it with the kit.
• Coolant, which is drained when the water pump is changed and refilled with the type the manufacturer specifies.

The auxiliary belt, which drives the alternator and the air-conditioning compressor, is sometimes changed in the same job too. Ask exactly what the quote includes so you can compare garages fairly.

What happens if the belt snaps#

The engine stops on the spot and won't restart. On many engines, after a snap, the pistons hit valves that were left open, and the repair means taking off the cylinder head and fitting new parts; sometimes it isn't worth doing. Other engines escape that kind of damage, but you can't know in advance how lucky you'll be, and the car is stranded either way.

If the engine has cut out suddenly and you have reason to think the timing belt has gone, don't try to restart it. Call a tow truck to get to a garage, so you don't make the damage worse.

Signs of a worn timing chain#

A chain usually has no replacement interval, but it doesn't last for ever. Get the car checked if you notice:

• A metallic rattle on a cold start that fades after a few seconds or stays.
• The engine warning light, with codes about camshaft or crankshaft timing; a diagnostic check shows which faults are stored.
• The engine runs roughly or has less power, with no other obvious cause.

Oil changed on time, to the manufacturer's specification, helps a chain last, because its tensioner often works on oil pressure.

What to ask the garage#

1. Which timing drive the engine has and what interval the manufacturer recommends for it.
2. What's in the kit: belt, tensioner, pulleys, water pump, coolant, auxiliary belt.
3. Which parts they fit: from which maker, and whether they are for your exact engine.
4. Whether they use the engine's locking tools, so the timing is set correctly.
5. Whether the job is written on the invoice with the dashboard mileage, so you have proof when you sell the car.
6. What warranty they give on parts and labour (see what a repair warranty covers).

How CariX helps#

In the free driver account, the timing belt change no longer gets lost among the invoices.

• Mileage: you enter it yourself, it comes from jobs and fill-ups, or from the monthly "How many km is the car on?" email; CariX works out your monthly average, so you know how fast you're nearing the interval in the service book.
• Your own reminders: you add a reminder for the next timing belt change yourself, and it comes by email.
• Warranties: the warranty the garage records on the job appears under "Active warranties" on the car, with an email 30 days before it ends (for a warranty in months).
• The car passport keeps the job, recorded by the garage, with the mileage it confirmed: the proof a careful buyer asks for.