I often see people commenting on forums about cambelt replacement intervals and cost, and it is quite obvious from a few of those comments that some people don’t really understand the importance of said belt.

Once upon a time, almost all four-stroke engines used a chain to drive the camshaft, but in the late 1960s and early 1070s, rubber belt drives became ever more popular.

Now many people still believe that a chain drive is more reliable and in many cases, that is true; but chain drives still fail, and the real downside of a chain drive is that when it fails, it is invariably more expensive to put right.

For those who don’t understand the workings of a four-stroke engine, the crank is driven round by the pistons, and the valves have to open and close in the right point of the cycle to allow fresh air in and exhaust gases out of the cylinders.

It is therefore obvious that the cam, which opens the valves, has to be timed accurately to the crankshaft. If the drive system for the cam fails, the valves will stop moving, but the pistons won’t and when they contact the valves, which remain open, it all gets very messy inside – and expensive to put right.

Toothed rubber belt drives are in the main very reliable, but as with all things mechanical, they do require routine maintenance – replacement – because the rubber will degrade over time.

Different manufacturers recommend different time and mileage intervals for replacing the cambelt, but as a general rule, 80,000 miles or five years, whichever occurs first is a good guide.

Get an estimate of costs

The cost of replacing a cambelt varies according to the vehicle in question – for example, a small hatchback with a small-capacity petrol engine might well involve as little as 1.5 hours’ work to replace the belt, while a light commercial vehicle, such as a Ducato, can be around 4.5 hours, and perhaps even longer if it is an A-class motorhome with more difficult engine bay access.

The point is, you need to get an estimate of the cost for your vehicle, not go by what someone paid in 1980 to have a Ford Escort belt replaced.

Another complication is the fact that many, but not all, belt-driven engines run the coolant pump off the camblelt, and the pump should therefore be replaced along with the belt.

The reason is simple – if the pump bearings fail, the belt will go slack and probably jump teeth, throwing the cam timing out and causing the pistons and valves to meet. Ask a workshop when yours needs replacing and what it will cost.

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