Knurled valve guides

OK.....let me explain what 'Knurling' actually is, and what its intended to do.........so everyone will make their informed opinions on what should be done....on his heads or on your own at some time in the future.....

After the head is tore down and cleaned......a tool that looks like a grinding pilot with a little snap hole on the side has a really small wheeled cutter that snaps into that hole. That tool is then inserted into the worn valveguide (,004 oversize and up), driven thru the guide hole with a speed reducer......essentially tapping the inside of the guide bore. All you are doing is raising a small burr in the hole. Sone tools actually look like a really long tap, threads and all with a small straight pilot on the end to guide the tap thru the center of the hole.
Usually....you don't even have to ream it back to size cause when you blow and brush out the shavings out of that valve guide hole, you shove the valve stem thru there the first time.....you resize it to where it needs to be,
Then.....if you put a good set of seals on top of the valveguide.....that helps hold the stem to the center of the valveguide hole.
Yes........I've seen knurled guides go gillions of miles......in the info given to the shops......they are a alternative to replacing the guides until absolutely necessary.

Knurling is intended on engines to last 10 to 20k milage wise. I've seen motors run 150,000 on knurled guides and you can flip pennies thru some of them...........

They're not made for racing or high perf......as the extra lift has a tendency to smooth your 'burrs' out on the guide bore.

1.Once your engine has a little wear.....you knurl the guides.
2.After about .003, you can tap and sleeve them with a kinda brass helicoil.
3.After that gets sloppy, you ream the guide bore out and put in your brass sleeve.
4.After that gets sloppy, you cut out that cast in guide for replacement drive-in chilled or bronze guides of your choice.........

After you tighten your guides up by whatever means.....then you can grind or cut your seats, replace them......everything concerning your valves rotates arount have good tight straight valveguides.........