The cambelt (timing belt) keeps the engine's pistons and valves in sync. If it snaps, the valves smash into the pistons and destroy the engine — typical scrap repair cost £2,500+. UK manufacturers specify replacement every 60,000–100,000 miles or 5–10 years, whichever comes first. Replacement cost: £350–£900 depending on engine.
The cambelt is the single most expensive part of car maintenance to skip. Here's why, and how to know when yours is due.
What it actually does
The cambelt synchronises the crankshaft (pistons going up and down) with the camshaft (valves opening and closing). If they go out of sync, the open valves get hit by the rising pistons. Bent valves, smashed pistons, often a cracked cylinder head — engine usually written off.
When to change it
Check your handbook or service book — it'll specify either a mileage (commonly 60,000, 80,000 or 100,000) or a time interval (5, 7 or 10 years). Whichever comes first. Time matters as much as miles — rubber perishes whether you drive or not.
Why you change the water pump too
On most engines the water pump is driven by the cambelt. Half the labour cost is getting in there. Doing the pump at the same time costs £60–£120 in extra parts; doing it separately later costs another £400.
Chain vs belt
Many BMW, Mercedes, Honda and some Ford engines use a timing chain instead — these usually last the engine's life, but check yours, because some chains (BMW N47 diesel, Ford 1.0 EcoBoost early models) are known failures.
Cost in the UK
Cambelt + water pump kit: £350–£900 at an independent depending on engine. Main dealer: £600–£1,400. Cheap compared to a £2,500 engine.
How do I know if my cambelt has been changed? — Service book stamp, or a sticker under the bonnet near the belt cover with the change mileage. If neither, assume it hasn't been done.
What happens if I just drive past the interval? — You're gambling. Some belts last 30,000 miles past interval, some snap on the day. There's no warning — it just goes.
More detail on: What is a cambelt and when should I change it?
The short answer above covers the usual case. Below is the extra detail a UK driver normally needs to act on it — how to narrow the fault down, what it should cost, and when it is worth paying a garage rather than carrying on. This is general guidance from a working mechanic, not a substitute for someone putting your own car on a ramp.
How to describe the problem so you get a straight answer
Mechanics diagnose faster when they get facts rather than conclusions. Give the make, model, engine size, fuel type, year and mileage; say exactly when the fault happens (cold start, motorway speed, braking, turning, first five minutes); say what changed just before it started; and list any codes, warning lights or recent work. A three-line description in that shape is worth more than a paragraph of theory.
What to do before you spend money
Run a free MOT history check to see whether the same item has been advisoried before — that history often explains a fault in one line. Check whether an open safety recall covers the component, because that repair is free at a franchised dealer. Then get the fault properly diagnosed rather than replacing parts in order of price.
What Bob would check first
Start with the cheap, common and visible: fluid levels and their condition, tyre pressures and wear pattern, battery voltage and terminal condition, and every connector and vacuum pipe in the area of the fault. A surprising share of electrical gremlins are a corroded earth or a chafed loom, and a surprising share of running faults are an air leak downstream of the sensor doing the complaining. Only after that does anything get unbolted.
When it is worth going to a main dealer
Three situations justify main-dealer money: an open safety recall (free), a live manufacturer warranty or goodwill claim, and coding or programming work that needs manufacturer-level software. Everything else — servicing, brakes, suspension, clutches, cambelts, diagnostics — an experienced independent will do to the same standard for a good deal less, and using an independent does not invalidate your warranty under UK block exemption rules as long as the correct parts and schedule are used.
Safe to keep driving?
Treat anything affecting brakes, steering, tyres, seat belts or visibility as stop-now, no matter how well the car appears to be driving. Overheating and low oil pressure are also stop-now: the damage curve on both is measured in minutes, not miles. Most other faults will let you drive gently to a garage, but if the car is in limp mode, losing fluid, or the fault changes how it steers or stops, get it recovered instead. Recovery is cheaper than a tow plus a new engine.
Get an answer on your own car
If you want this looked at properly for your exact vehicle, send the details and Bob will write back — make, model, engine, mileage, when the fault happens and any codes you have. You get a written reply from a qualified UK mechanic with 32 years on the tools, not a chatbot, and your money back if he cannot help.
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