[clivealive44]

Thanks for the detailed and interesting response.
I was reading an interesting post on a platform called "Quora", from a 30 year time served mechanic on what causes wear to cam belts, and cam chains. There was an interesting reply from a 25 year time served mechanic from the UK who said the following about the effect of the number of cylinders which an engine has on a cam chain - " the main issues as i see them are the increasing use of fewer engine cylinders meaning the time between firing cycles ‘jolting’ the chain is longer and, as a result the chain is jolted harder (3 cylinder engines are pretty much the norm now, where 5–10 years ago the same cars had 4 cylinders) the stop start technology fitted to many cars now puts more strain on the chains, the average UK motorist only does around 10–12k miles (many a lot less) so again, starting/stopping the engine and straining the chain, and the fact that the strain is now transferred into a single (simplex) chain instead of a duplex chain, (probably due to cost cutting) is also adding to the number of failures."

I have a copy of a chapter on the D24 (and D24t, and D24tic) engine from a Haynes Manual on servicing car and light van Diesel engines published about 1992 for professional mechanics. Interestingly, it gives the basic maintenance interval as 6000 miles, or 6 months, which ever comes first. It says "Volvo recommend that the engine oil (but not the filter) be changed at every 3000 miles on all turbocharged engines, and on normally aspirated engines operating under adverse conditions"
It says that the cam belt, pump belt, and idler roller should be replaced at every 12th maintenance interval, which equates to 72,000 miles, or 6 years.

My car was last done in 2014, at 220k miles, I normally get it done every 60k miles or less, it has now done 272k miles, which means it is due next year. I was half considering leaving it for another year, but I will probably get it done next year to be on the safe side. I have a client who is a 30 year time served Volvo mechanic, I'll ask him and see what he thinks.