Cam Belt Tensioning.
The original K series engine had a manually adjusted cam belt tensioner which is set using an external spring. This is then discarded after use to stop it jumping off into the cam belt! Later ones (and I think VVC) had a rubber sleeve fitted to prevent this from happening. The tensioner on the standard engine was changed at 97.5 MY to a spring loaded automatic tensioner that self adjusts to compensate for wear after initial setting, but the VVC and 8 Valve engines retained the manual tensioner. The cylinder head casting was changed to accommodate the different fixings of the new tensioner so they are not directly interchangeable.
The two different tensioners look like this:
Belt change intervals are 60,000 miles / 6 years (4 years on some models) for manual tensioners and 90,000 miles / 6 years for automatic. However, I think that most people accept 60,000 miles / 6 years as being safe for most engines.
There are three different cam belts available to suit the various engine / tensioner combinations plus the one used on the 8 valve engine -
143 teeth 23mm wide manual tensioner standard.
143 teeth 26mm wide manual tensioner VVC.
145 teeth 26mm wide auto tensioner.
After fitting the cam belt, the tension should be roughly set and then the engine is turned by hand for two revolutions clockwise. This both settles the belt and also gives the chance to check that nothing is going to lock up. Stop turning when the timing marks are lined up again and recheck that they are correct, then finally set the tension.
With the manual tensioner this is done by slackening off the fixings a little so that the spring tension can set the tensioner position then retightening the fixings. If the spring does not have a rubber sleeve fitted around it, it should then be removed.
The auto tensioner is set by slackening the fixing and then turning the tensioner with an allen key anticlockwise until the wire pointer lines up with the indicator notch. The fixing is then retightened. The action of the auto tensioner while setting up is shown in this video
. (he gets his clockwise/anti-clockwise mixed up! Turning anti-clockwise as shown is correct)
It is normal for the auto tensioner position to change as the engine is rotated, but it should return to the set position when the engine is stopped at the timing marks.