Why is my chair tensioner not tensioning ?

I'd feel more comfortable if he used a spare cam cap as a guide.
Since the threads stripped out instead of the bolt snapping there is no need for a cobalt drill. Regular HSS will do the job just fine.

 

Those are better ideas.

 

Since the original hole is being opened up, wouldn't a light touch with the drill allow the bit to follow the original hole? I would be more worried about tapping at an angle for the helicoil insert

 

Yes just drill once using the drill supplied in the helicoil kit using original hole as the guide. Still better with an old cap to use as a guide.

 

Though using the old cap will only allow cleaning up the original threads. The helicoil needs a larger bore.

 

Thanks guys, the threads are actually further down the hole and the top part is actually slightly larger... Maybe 7mm. So that will be a good guide already for drilling straight. I'm very good with drills and such so shouldnt be a problem. I reopened the head... Put the valve springs already in the right orientation. Only one was wrong haha, quite lucky still.
The gasket is gone though so that's a good waste of 50eu. Damn it.
I have ordered the helicoil kit for m6 since nothing local exists but I am taking a holiday for 3 weeks so back at it end of July.

Thanks

 

The top 7mm approx wide section is where the alignment dowel fits.