My 1951 G2 Trials

[murdo]

Have put aside the oil feed to head problem for the moment. I need to replace the valve guides and have new ones to hand and have made tools to do the job, but I am wondering what temp I should bring the head to before picking up the hammer. The vintage motorcyclist book doesnt mention a temp for this job. Any suggestions?

[R]

For fitting bearings (into the crankcase) the traditional quote was to get it hot enough
"that when you spit on it, it spits back at you" 

I'd think that alloy cyl heads would need to be at least this hot.
The last thing you want to do is split something in half because it wasn't hot enough.

AI suggests a broad range of 150 C  ++

Aluminium melts at a (moderately) lowish temp, with about zero warning, so don't overdo it !  (oxy torch, etc).
You don't want to soften or warp it either.
Chilling the new guides assists a little also.