One thing to remember when using the Volvo service recommendations. Hours relates to wear. Years or time in a marine environment relates to mechanical failure caused from moisture in the air or from water. In the 2016 Volvo Penta D3 owners manual the recommendation for belt replacement is every 1400 hours / At least every 8 years. That recommendation gives me a question mark! I read it as the engineers are thinking that 8 years is pushing it. At least in my interpretation means probably sooner but we don't want to state that in the manual.
If you are a cruiser that logs 200 to 300 hours a year on your engine after 6 years of cruising you will be replacing the belt kit, belt ,tensioner, and freshwater circulator pump. The belt will be at its point of stretch and wear if the tensioner is functioning properly. The D3 is a interference valve train motor. Meaning if the valve timing is off the piston hits the valves and in most cases destroys the engine. A loose belt or broken belt can cause this to happen.
If you are a cruiser that logs 100 hours a year and you look at the hour meter for service intervals you may have mechanical issues even though there is little wear on the engine and components. Example: timing belt wear is minimal but the tensioner has some corrosion and is not moving freely or because of time the spring tension is reduced and not sufficient. At 6 years you only have 600 hours and the belt wear is estimated to last 1400 hours. Why change it? Because of marine age.
The best case is you change the belt and tensioner at 6 years and 400 hours and it all looks like new. This means you have maintained a dry well ventilated engine compartment and your engine should last a long time. The other case would be the tensioner is weak and belt tension is marginal. This too is good information and a way of stepping up your maintenance by maintaining a dry, well ventilated compartment in the future.
Maintenance schedules using hours is for cruising boats that put several hundred hours a year on the engines. Maintenance schedules using season or year is for most boaters.
In tranmkp's case the hours were not much but 8 years is pushing it. Remember how the engines wrote the years, AT LEAST 8 YEARS. I read that as probably sooner but for marketing purposes we will say 8! Just my opinion!!
I know of several tensioner failures resulting in valve interference with D3 engines. The ones that I know of are in Ranger Tugs R25 and R27. I know of many raw water belt tensioners D3 that have failed too. Same principle. Good engine compartment ventilation and a dry bilge will help reduce theses failures. Its not hours that cause the failures it is maintenance and marine life.
Good information provided by tranmkp. I also agree that at eight years pulling the engine to do the belt change is the way to do it. It is a tight compartment to do the job. When the engine removed, it is a perfect time to clean the bilge and inspect hard to get at components . Clean up the engine and touch up paint. Engine mount inspection or replacement.
