Thanks yes, you are correct in that. A friend brought over some of the Loctite 567 that I mentioned and we tried it on one thread but looking at the specs, it is not suitable for this application. So I will remove that stud and clean the threads and start again. I think I will buy the Permatex stuff, although even the claimed 400deg F (204C) I think is a bit low for this position. I wonder just how hot those studs do get on a hot day and right next to an exhaust port? We would never know unless there was some accurate sensor that could be screwed in there. Those laser temperature probes are great and could be shined onto the stud itself but the temp of the actual thread inside would be far hotter. I know it is also right next to the coolant which is running at less than 100deg C, but it is less than 10mm away from the wall of the exhaust port. I'm probaly just being too pedantic. As far as the threads go, they are not damaged, it's just that the studs are more loose than I would prefer. I had an idea with that Permatex. Tell me what you think... I was thinking of getting a small screwdriver and loading the threads inside the heads with the Permatex thread stuff, letting it cure, then when it had set, inserting the stud in with more of the Permatex on the stud. I don't see why that shouldn't give a nice tight fit. Moper mentioned retapping - of course that is the ideal solution (factory is 5/16, not 1/4 like he said) so I would be tapping up to 3/8. However in the OP I mentioned that I don't want to pull the heads off just to do that. I'm selling the car but even if I wasn't I would not pull the heads to do that.
