Ahem, er, ok, yes, I do tend to borrow it quite a lot! However, I do seem to end up setting or checking an awful lot of belts when I do borrow it - I think it was four last time!
To be honest, the spring on the tensioner on my S2 is (was) pretty good at setting the tension about right. About right, because I am not so sure quite how accurate the gauge really sets it... But I do it "by the book"... I am starting to have doubts about how critical the tension is, but I'm not prepared to risk it - I think the balance shaft belt is more the problem - it is very difficult to judge the tension on a belt which runs so slack.
However... on top of that, there is the fact that there are two belts running in one housing. If one snaps, it will pretty much certainly end up snarled in the other and break that too (ok, that only happens one way - if the timing belt snaps first it possibly won't break the balance belt, because the engine will have stopped quite possibly before the balance belt gets a chance to snap, not that it matters because the damage is done anyway). So for whatever the average is for belts to snap... the odds of damaging an engine through belt failure on a 944 are theoretically halved, because you have two belts waiting to fail. Twice as many 944s will suffer engine damage through belt failure compared to another belt driven (interference engine with belt drive and no balance belts, or at least not in the same housing) car.
Reference the extra load on a 16v engine, my guess is it is the number of valves which will make the difference rather than the number of cams, as it is the valve springs which really apply the load - in comparison turning the camshaft will be relatively little load. I'm not sure if the valve springs might be lighter anyway, because the mass of the valve is less...
The tale I usually tell is of an ex 944 owner who stood at the bar and telling me it was totally unnecessary to use the official tool to set belt tension - the usual method of 1/4 a turn is all you need to do... I'm sure he didn't see the irony of later telling me how lucky he was in only having to replace two valves after he had a timing belt failure...
