Basically there is a design fault in the original Honda design. The spring inside is the week point and they can snap/break so fails. This causes the tensioner to loose it's tension to the point of the cam chain going slack enough for timing to go out and valves can hit the piston as it comes up. Not good

There is no warning and all one can do is take preventative measures in the form of a fail safe mod on the honda auto tensioners so if it fail it does no damage but will need replacing or go for full manuals and be done with it.
Some links regarding the Cam Chain Tensioners (CCT's)
You can either go for the stop mod
http://www.vtr1000.org/phpBB3/viewtopic ... 31&t=19416
Which is the Honda auto CCT's that are converted to a fail safe. So when it does fail, it don't send the valves crashing.
Or
You go for the full manual conversion, your options are here
http://www.vtr1000.org/phpBB3/viewtopic ... 16&t=22720
As for fitting manual see the guide in my signature.
(:-})