Get a Cummins manual or search on here. There are many threads on this subject, all with little tidbits of info. A fellow member did them for me, he's a mechanic type, I'm not. Anyhow, I might suggest picking up an extra collet (valve keeper) or two, they're cheap and you never know when yer gonna drop one and not be able to find it. Also it's a good time to replace the valve cover gaskets. If your's are black, the new ones are supposedly a better design and the one's I've seen are gray.