The previous owner of my Ph2 172 had the cambelt changed at 49k miles back in March 2007. Five years on and the mileage is now 71k so 21k more. When should I think about getting the belts changed? The reason I ask is I know some manufacturers specify a mileage or period, depending on what comes first, for example, a Lotus Elise is now every 5 years regardless of mileage.