Re-torquing 1.6 Hdi injector bolts

[MattBLancs]

Sorry for resurrecting an old thread but I am trying to get the studs out of a 2009 DV6 and it strikes me that something has been overlooked (or I am being daft which is always possible).

I have 2 studs out already and there is no thread in the rocker cover, the reason the stud is so long is it screws into whatever is below, presumably the cylinder head or a ladder. I haven't had to open one up yet so I would know but it is definitely not the rocker cover that holds the studs.

Yes, correct, a clearance hole in the actual rocker cover, the M6 section is threaded into the cylinder hear itself below.

The cover to cylinder head joint is metal to metal (I can't recall if there is an O-ring here too?) And there's nothing to encourage the oil out from under the bolt head beyond it generally being flung about by the cams, rockers, valve springs etc.

My question is this, if this is a torque to yield bolt, which the extra 65º suggests, and the yield is in the M6 section below the flange where it is underneath rocker cover, why don't these studs all leak oil? Let me explain. The only thing that seals these studs to the rocker cover and keeps the oil inside is the fact that the flange is a tight fit. Ever if the yield is only a few thou that extra length would mean the flange was no longer a tight fit on the rocker cover and it would leak.

These studs don't leak so something doesn't add up. I suspect they are heat treated and they stretch above the flange but if that is the case why are they snapping below the flange. Any thoughts....

Low torque setting + angle tighten is often used with torque to yield fixings but I believe it is also more accurate/consistent method, so perhaps that drives why specified for here?

I can't really get my head around these oddball studs at all! If I were to design this, would be a straight length of M6 (or M7 if needed = seems unlikely) threaded stud, screwed into the cylinder head. Then rocker cover retained with a standard M6 hex nut. Then injector retained with another M6 (possibly Nyloc) nut = job done! No torque to yield nonsense, no studs of differing diameters, no daft tubular Allen head nurse for the injector clamps!

Furthermore, backing off the rocker cover nut up the threaded stud, would allow you to pull the injectors up and off potentially too!

[citroenxm]

Is there room on the thread to lock a second nut to the ones already holding the injectors in place? Perhaps a pair of thinner nuts would work.
A technique taught to me by my dad.

https://www.boltscience.com/pages/twonuts.htm

No, as they are a Tall Nut in which you use a 7mm Allen key to tighten them, on the 16v, Havent heard of the 8v ones comming undone at all..

The stud is a strange one, as it is screwed into the head, but the thread under the rockercover is SMALLER then the thread the clamp nuts go onto, which as said above if over tightend can snap the lower part, and of course they wont draw out as under the rocker cover theres a Buldge that the rocker cover uses to help keep the stud toght in the head!