What Happens If Your Cam Belt Snaps While Driving?
By Derby Cam Belts ·
A snapped cam belt is one of the most expensive things that can happen to your car. Here's exactly what happens when it breaks, and how to make sure it never happens to you.
The moment the belt breaks
The cam belt keeps the camshaft and crankshaft in time. When it snaps, the camshaft stops turning, the valves stop opening and closing, and the engine cuts out instantly. You'll lose power steering assistance and brake servo help too, so pull over safely.
Interference vs non-interference engines
On a non-interference engine, a snapped belt usually just means the car stops — fit a new belt and it may run again.
Most modern engines are interference engines. The pistons and valves share the same space, so when the timing is lost the pistons hit the open valves. The result can be:
- Bent valves
- Damaged pistons and cylinder head
- Broken camshaft or valve guides
- In the worst case, a replacement engine
How much does it cost to fix?
Repairs after a snapped belt often run into four figures, and on older cars can cost more than the car is worth. Compare that to a planned cam belt change from £300 fitting plus the kit — see our Derby cam belt cost guide.
How to avoid it
- Check your service history for the last cam belt change.
- Follow your manufacturer's interval for age and mileage.
- Replace the tensioners and water pump at the same time where advised.
- Watch for the warning signs of a failing cam belt.
Frequently asked questions
What happens if a cam belt snaps while driving?
The engine cuts out immediately and you lose power. On an interference engine the pistons can hit the valves, causing major engine damage.
Is a snapped cam belt worth repairing?
It depends on the damage and the value of the car. On some cars the repair costs more than the car is worth, which is why replacing the belt on time is so important.
How do I know if my engine is an interference engine?
Most modern petrol and diesel engines are interference engines. Text us your registration and we can tell you.
Text your reg for a quote
Tell us if you want fitting only or supply and fit and we'll get back to you with a price.