Sounds easy enough, yeah? Wrong - not on my piece of s*!t van!
I can get screw the studs about 3/4 of the way in but don't seem to be able to get them in any further. This is on the left hand side of the engine and then the left hand side of the rocker assembly. (I did the right side last week and the studs went in easy but they are all the same size, genuine studs so why am I having so much trouble on the left side?).
I have tried spraying the thread on the head and the studs with Plusgas and WD40, doused both in 3-in-1 oil, covers the studs in copper slip then tried screwing in - all to no real success. I have managed to get the one on the right in now quite far but it still has about 2 'threads' to go before it is all the way in. I have only managed to achieve this by getting some grip pliers and painstakingly turning a fraction at a time. I can't seem to move it any more but that might be from the effort I've already put and me not being able to feel my hands anymore in the crappy weather. I have also tried the nipping 2 nuts together on the same thread but again go so far then hit a brick wall again.
Has anyone got any suggestions on how I might get these in?

Also, I had to split the old nuts off. These seem to be 8mm threads. This might sound stupid but can I use Nylok threads to replace them or will the heat generated in the rocker area damage these?
Finally, as the studs have been taken out completely and replaced, do I now need to ensure that I do re-set the tappets? Previous posts suggested that on the air-cooled, as the engine hasn't turned, there was no need to do this but if the studs haven't gone all the way in, I'm guessing the rocker assembly may be slightly moved and therefore the tappets may need resetting after all?
Thanks in advance for any comments / help.
Chris