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.

[cardan]

Slow heating in the oven, for caution...

Best also to do some careful measuring to asses the level of interference of the fit. I'm not sure exactly what is should be - look it up - but it's only small - I doubt it's more than 0.001" or so. It would be a pity to heat your head, cool your guides, and still find the things stuck half-way in!!

Leon

[murdo]

Using my gas BBQ I took the head casting to about 180 deg (might have cooled a little by the time I got it on the wooden blocks) and only took two light taps to remove old guides and three to seat the new ones. The guides needed a light touch with a reamer after cooling down to get a nice sliding fit, but the exhaust was a little off centre when I put some bearing blue on the valve and fitted in the seat. Took a bit with the stones to get straight, the intake was good. Ended up with good seal and seat widths.