Valve guides come in several different types. Most are an interference fit. The old valve guides get driven out, and new ones driven in. This usually happens pneumatically. Some valve guides are actually screwed into place. The Jeep ones you mention, as well as most of the American made vehicles are driven in/out.
There are basically three ways you can fix worn valve guides:
- Complete Replacement - This is buying new valve guides and replace the old ones. This involves taking the old ones out using a pneumatic driver. The driver is setup with a rod which goes down the middle of the guide with a cap which holds the top. Then the air is applied and the old one is driven out from the top out through the valve port. The new one is then driven into the same spot using the same tool and procedure. The guide is usually trimmed to size once in place.
- Knurling - A less expensive and more problematic method to fix the valve guide is to knurl the inside of it. What this does it basically pushes a pattern into the valve guide which squishes the valve guide a little bit. The only place it can squish to is to the inside, which takes up the gap and holds the valve stem in place. The issue with this is like most cheap fixes, it doesn't last long in the grand scheme of things. Since there is less guide material actually holding the stem, it wears rather quickly. The other issue is if it's not done correctly, it can actually become a pump and press oil right into the port which causes the engine to burn oil. This method has really fallen out of favor because doing the next method came around and basically replaced it.
- Liner Insert - This is a process which is a bit easier and cheaper than completely new guides, but lasts much longer than knurling. What takes place is a new liner is given to the old guide. It's like giving new life to the old guide. The machinist will prep the old guide by reaming it out to the proper size. Then the insert will be pushed down into place. Once in place, the new guide insert is reamed to near size which is just shy of the size needed for the valve stem to fit properly. This not only sets the insert to the proper size, but also binds it in place to the old guide. The tops and bottoms of the insert are trimmed to size, then the final honing is done so the insert will function just like a new guide.
These are the general ways guides are changed or fixed in a lot of American vehicles. There may other methods and different guides used, but these will cover most of them. Needless to say, you need to lap the valves once the new guides are put in for proper valve seal. The new guides will not be in the exact same place as the old ones, so this is an important step in getting the guides back into proper shape.