Can the wise men of this forum please advise how tight the head studs should be tightened when replacing them? I’m sure I have seen it on this forum that they are only loosely fitted which seems counter intuitive. In this instance I’m replacing long studs in a series 3 xj6 engine.
Well, if you think about what happens when you tighten the stud it makes sense that no torque should be applied. The torque indicates tension over the stud - clamping force - and when you have enough thread engagement (make sure to blow out the hole in the block so it doesn’t bottom out on crud) you are good. Torque won’t really help there; one worry is that the stud comes out while removing the acorn nut the next time but apart from that the way everyone does it seems to be fine. I don’t know if a loose fit or slight tightness is wanted but more torque than absolutely needed can’t be any good.
The method we used back in my Navy and power plant days was to bottom out the stud when installing it, then back it out one turn. The reason was to prevent thread stress when stud was heated, and it also makes them easier to remove.
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Do they need replacing?
I hope you looked at yours, they can foul badly and then they break and the block is junk 
As I said the torque is needed to stretch the bolt and the lower end shouldn’t really be torqued down too much. A little might be okay, is it?
Look in the first posts of the Jee-Type thread.
Oh yes. I even liked that 
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Many thanks chaps. I had to remove all of the studs in Oder to get the head off as sufficient crud had developed around the studs such that I couldn’t lift the head up. Fortunately they all released without much fuss.
I will replace the studs as a matter of course.
Off for an acid wash, I expect? Paul.
Acid wash Indeed Paul. the engine is in surprisingly good condition from what I see at the moment. ill have the sump off today so that’ll allow more investigation. but generally things seem ok with no ridge at the top of the bores and so far no obvious damage in the bores. The head is very clean and the valve clearances reasonable. it does look like the head has been off at some point as it has the later style head gasket. I have no history for this engine. i bought it as a COVID 19 frustration relief project!
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Finger-tight, or not much more. They are stretched to spec when the nuts are torqued. Screwing them into the block tighter does not improve their function. I would personally use a antiseize paste on them. You can read a great deal about best-practices for threaded fasteners in the technical section on the ARP bolts website.
That looks like a Payen gasket. Put one in my XJ6 a few years ago - been good! Looks like it has has regular oil changes. Seems you got lucky. Paul.