I have heard that in the majority of cases failure is mainly caused by tensioners that have reached the end of their life and cause the belt to jump off.
Her indoors has 52 reg 2.0 16v auto Scenic and I have a 2001 1.4 16v Scenic. The engines are virtually identical but valves and pistons are different sizes and the 2.0 doesn't have a throttle cable.
I was driving the 2.0 18 months ago when one of the plastic cam belt rollers decided to part company with it's bearing the belt got pretty chewed up but didn't break! When I took the cylinder head off I found most of the valves were bent but caused very little other damage. The car had done 55,000 but at 7 years old was 2 years over the belt time service interval but within the 71,000 mileage service interval.
back in February armed with the knowledge gained with the above repair I bought a cheap 1.4 Scenic the belt had snapped in 2 most of the valves were also bent all rollers seemed okay though I replaced them anyway. The car had done 66,000 but at 9 years old was 4 years over due a cam belt change.
On my scenic, the belt and tensioner were replaced at 53k miles then again at 90k. Car now has 114k on clock.
Yes I think you were wise I think that the Renault service intervals are rather optimistic and from what I have read a sales ploy to give the impression of low service costs.
I would not touch anything with the variable valve timing though in later cars.
The 1.4 is pretty gutless compared to the 2.0 which has a dephaser pulley but I don't think having variable inlet timing on the 2.0 makes a lot of difference? Though if it ever starts to rattle I think I will replace it with a normal pulley.
We have now done around 2000 miles in the 1.4 and 5000 in the 2.0 with no problems other than I have noticed both engines seem to use a lot of
? around 1 litre per 1000 miles? thought that apparently is considered to be within normal limits?