Valve guides
 

I've seen a couple of different valve guides in my limited experience with 911 heads. One has a shoulder that rests against the head, the other doesn't, and seems to require care (tool) when installing to get the appropriate height. Are either of these considered OK? Is one better than the other, or is the the type of material i.e. silica bronze, the best determining factor? Thanks in advance!

The after market guides or most have the shoulder, I believe all OEM will not and you need a stop to install them. I like the phos bronze guides, at least for the exhaust side. Price has gone way up on this stuff too.

Thanks again Craig. Do you know if the phos bronze guides are available in either style? If they are, then I would imagine it's just a matter of making a stop, or using the shouldered guide.

The Canyon brand (with shoulder) comes in two types, 93010432150 manganese bronze and 93010432151 phos bronze as first replacements, as I remember, don't have my book right handy. You can search the #'s right here.