Mine had the belt just flapping about because of the failed tensioner and doesn't *appear* to have bent any valves (no visible marks on the pistons). Could yours have just been chain tensioner noise?
I have a brand new engine waiting to go back in mine - I will check how the belt behaves on that and report back. I'll not get to it until Tuesday though.
You can visually check the timing to see if it's close. Turn the crank so that the notch in the pulley lines up with the mark on the lower belt cover (about 1 o'clock). The four holes on the cam shafts should all be horizontal - measure with a straight edge, or even a bit of string. Obviously you can't set it like that, but you can tell if its wrong.
I can see the argument for the belt going slack - the roller cam followers allow the cams to jump around when they are coming off the lobe, compared to tappets which don't behave like that. As the cam jumps round it could pull the belt tight in places and loose in others. Turned by hand the tensioner may not be able to accommodate this. If it does behave thus, I can't see how it could possibly do that with the engine running without tearing itself to bits. Rotating inertia, oil pressure, etc should see to it running smoothly. Of course all of this is conjecture until either I have a look at my factory engine or an expert chimes in! I would not claim to be an expert on the 40V.
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