I stand corrected but in fairness I did say there was two cams.kind of implies 16 or more valves.

Why do people keep asking this question? It's hardly a deal breaker either way. On balance I prefer belts, but I wouldn't turn down a car with a chain engine.

Then the handbook would say that. I'm assuming these questions are from people in the market looking at various cars and the belt/chain question is a deciding factor. Weighing up the possible high cost of replacing a rattling chain with the almost certain moderate cost of a replacement belt, I'd still err on the side of a belt. But I wouldn't turn down a car because it had a chain engine.

I'm looking at ulez diesel estates. The astra 1.6 cdti is a strong candidate but replacing the chain is £1200-2000 wheres replacing the cambelt on the 1.6 petrol is £300ish. That's why "we" keep asking

But my understanding, supported by my limited experience (of old cars, many of which were pushrod and so mostly avoided the dilemma) was that you probably would not have to replace a chain, but you probably would have to replace a belt.

Belts have an "official" service life.

Do chains?

In theory on most engines a timing chain should last the life of the vehicle*, this was the case for many years with only the odd exception but in recent years some engines from German makers have suffered with timing chain issues, obviously a timing chain is a more involved replacement than an external dry cambelt, the new wet cambelt designs i would humbly suggest are the worst of all worlds and i wouldn't touch one with a barge pole.

* will qualify that 'should last the life of the vehicle' with assuming some sensible routine servicing involving regular fresh good oil kept topped up between services has been the norm, some judgement about previous care can be gathered from a service history.

Overall i'm as happy with a belt drive as a well designed chain system, assuming that belt replacement has been thought about in the original design, anything above £400 belt replacement costs (if that includes a new water pump if foolishly driven by said cambelt) to me suggests a poor design.

At least with a timing chain the water pump won't be part of the engine timing system, there is no earthtly reason for the water pump to to be timing belt driven and the best designs avoid this.