Cambelt replacement, done with locking tools and not by eye

Why the time limit matters as much as the mileage

A cambelt is a toothed rubber belt. It ages whether you drive the car or not. A five-year-old belt on a car that has done 20,000 miles has still spent five years being heat-cycled every morning and sitting under tension every night, and the rubber hardens and the fibres inside lose their grip on it.

This catches people out constantly. Low-mileage cars — the second car, the retirement car, the one that only does the school run — are exactly the ones that arrive here on the back of a truck with a snapped belt and a ruined engine. Whichever comes first means what it says.

What happens when one lets go

Almost every modern engine is what is called an interference design: at some point in the cycle the valves occupy the same space the pistons pass through, and only the timing belt keeps them out of each other's way. When the belt breaks, the camshaft stops and the crankshaft does not.

Within a fraction of a revolution the pistons hit the open valves. Valves bend, guides crack, pistons get holed, and on a bad one the cylinder head is scrap and the block is damaged too. A repair like that runs into four figures — frequently more than the car is worth. Against that, £450 every seven years is the cheapest insurance in motoring.

What Erdi actually does

The whole reason a cambelt job varies so much between garages is what gets replaced alongside the belt, and how carefully the timing is set. Here is the standard here:

• The full kit, not just the belt. Tensioner and idler pulleys are bearings. They have done the same miles and the same years as the belt, and a seized idler will destroy a brand new belt in minutes. They go on together.
• Engine locking tools, every time. Cam and crank are locked at their timing marks with the correct tool set for that engine — not lined up by eye against a paint mark, which is how a job comes back a tooth out and running badly.
• Two full turns by hand before it starts. The engine is rotated through two complete cycles and the marks re-checked. If anything is out, it is found on the bench rather than on the road.
• Auxiliary belt and seals inspected while it is apart. Front crank and cam seals are right there, and a weeping seal will contaminate the new belt. If one needs doing, you will hear about it before it is done.
• A sticker under the bonnet. Date, mileage and the next due interval, so the next owner — or the next mechanic — is not guessing.

The water pump is in the price, not on top of it

On the majority of engines the water pump is driven by the cambelt and sits behind the same covers. The labour to reach it is already being paid for, and replacing it separately eighteen months later means paying most of that labour a second time.

Plenty of garages quote the belt alone and raise the pump once the car is in pieces and you are in no position to argue. Here it is simply part of the £450 — belt, tensioner, idlers and pump, one figure, quoted before the car arrives.

On engines where the pump is driven by the auxiliary belt instead, it is a completely separate job and it does not need touching. You will be told that too, and the price comes down accordingly rather than the pump being fitted anyway because it usually applies.

Chain-driven engines

Some engines use a timing chain instead of a belt. Chains are often described as "lifetime" components, which is optimistic — guides wear, tensioners fail, and a stretched chain rattles on start-up and eventually skips. If your engine has a chain and it is rattling, that is a real job worth doing properly. See engine and gearbox repairs.

Booked in from Bristol, Bath or anywhere in the Mendips

A cambelt is a full-day job, which makes it the worst possible thing to arrange around work. This is what the collection and delivery service exists for: Erdi collects the car in the morning, does the belt, and brings it back. Free within 5 miles of the workshop, and priced per postcode from Bristol, Bath, Frome, Wells and Glastonbury.