Down load the manuals here
https://foc-u.co.uk/index.php?action=downloads;cat=2Highly unlikely your tensioner is giving trouble but it is far more than likely to be a worn cam chain or the tensioner has not taken up the slack yet. Common for engines with cam chains to rattle before the tensioner takes up the slack because chains do not wear evenly. Only time I ever saw an stuck Fazer 600 tensioner was on a bike that was out in all weather and not used for 4 months under a tarpaulin not to far from the coast and the tensioner was rusty, as was the rest of it
You only need to remove the tank or prop it up securly. Pull up the plug caps carefullyRemove all the cam cover screws. Remove the Rotor cover and tie it up out of the way.rotate the Rotor anticlockwise until the 'T' mark lines with the joint between the crankcases at the front of the engine.See picture
Lift the cam cover and check the timing marks see picture of the actual cam and cap marksmark.
If the cam does not line up close to the cap then rotate the rotor a full 360degreeds and line up the rotor marks again.
If the cam marks are less than 5mm off to the rear then the rattle is probably from the tensioner not having taking up the chain slack yet.If 5 to 10mm off to the rear chain is wearing and tensioner has not having taken up the slack yet.More the 10mm off to the rear, the chain needs to be replaced as the tensioner is probably at the end of its adjustment.Might be worth checking the tappats as you have the cover lifted.
When you are putting everything back, put ordinary garage grease not silicone on the cam cover gasket and make sure it is back on properly.You can be liberal with ordinary grease as it the excess melts off
