intermittant misfire

[wildchild74]

Highly unlikely the tensioner is a problem, mostly like a wearing chain or valve clearance to big.

Cam Chains like drive chains do not wear uniformly they have loose and tight spots. This causes a light rattle especially on startup and the only know cure is to replace the chain.

What mileage is on the engine?

The tensioner is easy enough to remove if you still want to.

Remove the alternator/Generator cover.
Rotate the the crank anticlockwise until the T mark lines up with where the top and bottom crankcases meet.
Some will say you do not need to do this, but it is the best position to have the chain in when removing the tensioner.

Do not rotate the crank when the tensioner has been removed

Remove the 10mm bolt at the end of the tensioner. There is a ball bearing within the bolt, don't lose it.
Don't lose the copper washer on the bolt
Remove the springs (one is inside the other)
Loosen the two allen bolts and carfully remove the tensioner.  There is another ball bearing inside in the tensioner don't lose that either.
If your lucky the gasket will remain intact, if not replace it. It is probably best to replace it anyway.
Lift the ratchet and push back the tensioner.
Oil it up and with the ratchet held off the tensioner push the tensioner in and out of the housing a few times.

Replacment is more or less the reverse order of the removal.
Tensioner pushed back into the housing
Gasket
Tensioner body
Tighten the Allen bolts to 10Nm
Ball bearing
Springs
Push them in to the tensioner (You will hear the ratchet clicking over the ratchet teeth)
Put Ball Bearing into cap Bolt and copper washer on the bolt.
Put it on the tensioner and tighten it to 20Nm

Now rotate the engine slowly two full turns. You will probably here the ratchet taking up a little more slack.

You might as well check the valve clearances as you have the Alternator/Generator cover off if not

Put the Alternator/Generator cover back on and tighten the Allen bolts to 12Nm.

M8 your a life saver thanks for the info... why do i need generator cover off so i can turn engine over by hand?? And does the rocker cover need to be off to check clearances i presume yes the reason i ask this is because the mechanic said it could be down to the valve clearances the misfire but its not hard to start.... thanks again
Gaz