vlave guides are rebuilt with bronze walls. i use the walona system where the guides are taped and the a bronze insert is threded in then a expander ball is driven through to lock it in place then it is reamed to size. there is another sytem that is close to that it is called the nu-way.
now about knurling it was popular at one time but then people found out it lasts about as long as it takes to talk about it. think about it this way. you take an already over size hole run something through it that raises some high spots then you ream more metal out of that hole.
just putting seals on will last a little while till the valve rattleing around in the guide
wears them out too.
so the way it works is after takeing the head apart getting it clean the most important thing is the guides if they are not to size or rebuilt right then everything else is just throwing away good money
