Cylinder heads are a lot more complex than you might think. They look simple enough and they are to some degree but I'm learning from a real pro that I need to learn more.
If the ball stud won't screw down anymore, guess what? You're screwed. That thinner lash pad isn't going to help you at all even if it gives you some clearance. It may let the valve close so you will get some compression but it will damage the valve guide in the process if the guide is still tight.
The geometry of the valve rocker is such that when you run out of adjustment at the ball stud the rocker will be too low at the ball stud end. When the cam pushes on the rocker it should move the valve straight down without any lateral deflection. Normally this is what happens but once you get the rocker too low it will start pushing sideways on the valve. You can ruin a whole set of new valve guides in only a few miles of running. The engine will smoke forever until you fix it which you want to do right away. The easy cure is to use shims under the cam bearings once you know the valve guides are OK.
If the guides are new but damaged this way we sleeve them with paper thin inserts. If they're old they will have to be replaced. Installing a new valve guide should be easy, right? It is with the right equpment. We heat the head in an oven and freeze the guides. The top endge of the guide should be completely square to the hole. On our engines you want about .0015'' clearance between the valve stem and the valve guide. The valve should drop into the guide yet have no real play when they're right. Done like this they will last far longer than too loose or too tight.
Ever find that you can't find the miss in your engine? It doesn't really miss at idle and pulls hard but as soon as you get up to speed and level out, there's that miss again. You look at everything. Wires, plugs, cap, rotor, injectors, valve lash but nothing's wrong. A compression test will show a low cylinder or maybe one that's a lot higher than the rest. Nothing seems to make sense......
What you have is a lean miss fire caused by oil leaking into the cylinder. The rings can be badly worn or you can have a bad valve stem seal, either way there's just the right amount of oil getting in. The oil will upset the air fuel ratio and will burn very hot. The extra heat may cause pre ignition but you probably won't be able to hear it. This cylinder will get scored from the heat and the rings will be damaged. You would think all that extra oil might keep things well lubed but it really tends to cause more damage. And the worse thing is you won't see all that much smoke because it's just the right amount oil leaking in. Any less and it won't be much of a problem and any more would be easily seen.
I didn't believe it at first but now I do. There's no simple fix either. Some engines will do it and some won't. Fresh rebuilds are more prone to this because everything is still tight. It will be caused by the cylinder head in almost every case but will damage the cylinders in less than 500 miles if the leaking is really bad. This is why you want to pay attention to valve rocker geometry.
These two problems, valve rockers and lean miss fire are different but related in terms of engine damage. The lean miss is usually long term damage and the hot running cylinders will be more about leaking oil coming through the valve guides after a rebuild or at least with normal compression. The higher compression tends to burn up the oil which is why you won't see it very much. You will be able to smell it though.
Don't confuse this with an old oil burner. It's worn enough that you won't score a cylinder wall. The miss in that engine is from oil fouled spark plugs.
The lean miss engine will have darkened plugs on any bad cylinders even if it has good compression. New plugs will stay clean for a short drive just to add a bit of confusion. This is probably one of the hardest things to nail down that I would normally run into.
