Originally Posted by whalebird

Rus, I searched for a DIY on this with no good references. I may need to dig further. This is an easy check to perform and also to adjust. If one knows what to feel for, it can be done with your fingers and not even having to "look" at it.
The rocker should wobble back and forth around the area of the rocker shaft located in the middle of the shaft. Meaning the rocker should be centered on the shaft. The deception here is that the shaft "bosses" in the cam tower are thicker on one side of the rocker, but the thick boss is on the opposite end of the shaft on the other bank of cylinders. In short, the rocker shaft is rear-centric on one side of the engine, and forward centric on the other side albeit the shaft is divided evenly by the rocker itself. I don't recall which bank is which.
To relocate a shaft that has migrated in either direction is pretty simple. The worst part is getting the required allen wrench to fit the binder bolt. I have a garden variety allen wrench of the correct size(5mm, maybe 6) that I cut short at the bend to fit in the tight quarters of the binder bolt. The binder can be loosened and the rocker can be relocated forward or rearward then tightened with the said allen.
Snafu #1: the cylinder being observed must be at TDC before the rocker can be moved, otherwise the cam has it loaded with valve spring pressure. Thats one reason this is good practice during a valve adjust.
Snafu#2: the binder bolt is not loosening/tightening without turning the entire rocker shaft. For this, the binder has an allen wrench provision at it's opposite end for countering...requireing another short allen wrench.
My disclaimer: My info here is from memory and it's been a while since I've been inside one of these motors, thus my intentional lack of details. Details like when do you know the shaft is centered? IIRC, the end of the shaft should be flush with the exterior of the short/thin boss in the cam tower. Tool selection may be open for debate, also which end do you loosen, and which do you counter upon (it's not hard to tell). So, I would encourage anyone in audience of this post to seek another reference, or maybe someone with better working knowledge will clarify. Ed, you just did this on the 3.4,no? A Bentley manual may help, though I never used one. The FSM will be the last word.
Shifted rocker shafts are not uncommon, but not an everyday occurrence either. I have had numerous cars that had this situation, and a 930 that altogether dropped a rocker. One indicator of a loose/migrated shaft is an oil leak in the area of the head/cam housing union - or the area above the heat exchanger around the oil return tubes. There may also be an audible ticking for extreme cases.
For me, this was always a part of a valve adjustment, and I would happily return any shifting rocker shafts for no charge to the customer. It's very easy, and may prevent major top end damage, win/win/win for the mechanic/car/customer.
I hope others will post to clarify my abstract here. I have to imagine this is covered in other threads and I will search. I'll post a link if I find one.