Modifying the Cam Lobe Lubrication Spray Bar
Every M30 engine has the same two potential issues - first, one or both screws holding the oil spray bar loosen and drop out over many 10's of thousands of miles. If the valve clearances are checked regularly this is not a problem as you will catch it in time, otherwise the reduction of oil lubrication to most of the cams will result in excessive wear.
The reason for the failure is obvious to any engineer or anyone familiar with simple physics (except apparently the original designer.) Differing thermal expansion between the aluminum cylinder head and the rigid steel tubular oil spray bar "work" the screws over every hot/cold cycle. The screws would not loosen if the spray bar was not "over-constrained," meaning with the two guide brackets it only needs a single screw to be fully held in place. That would allow differential expansion to take place either side of the fastening point.
The solution is to safety-wire the screws in place. In a pinch use Loctite, but be careful to degrease the mating surfaces and don't drip Loctite into the cam bearing.
In addition, there is an issue with insufficient oil supply to the spray bar at idle to ensure it remains full. Since the engine sits slightly down at the rear (like most RWD cars,) oil just runs downhill to the lowest of the spray holes, in this case the rear cylinders.
On a closer look you can see that the spray bar is a steel tube with capped ends being fed by two oil sources (i.e. the two middle cam bearing housings) and supplying six jet locations (the six pairs of cam lobes.) When oil flow is low (that is, at idle) the oil tends to migrate downwards towards the lower (rear) end of the tube, starving the higher (front, cylinder 1) cam lobes.
As a simple solution, since there are already two equal flow-rate sources of oil available, it is logical to simply segregate the flow into two streams such that each source supplies exactly three sets of lobes. The front supply point will now not loose oil flow to the rear three jets.
Conveniently, all you need to do to accomplish this is to crimp-closed the center of the spray bar (see pics.) I should add that you remove the spray bar by tapping it carefully to the rear and lifting it out of the front saddle first. On replacement there is a arrow stamped into one end that points forward. Needless to say, never loosen the cylinder head screws unless you plan on removing the cylinder head, however you may want to check them for tightness while they are accessible, as I found a cylinder #4 screw slightly loose.
If I had to do this mod again I might also just cut the bar in the middle after crimping, and permanently solve the first problem at the same time.
You can make the crimp with sockets and a vice, or vice grip pliers.
The tube material is quite soft and therefore significant care needs to be taken when tightening the two banjo screws. I found that using the specified torque will slightly crush the tube. Since you are no longer relying on tension to secure the screw, there is no need to tighten it past providing an oil seal.
