I'm pretty sure the screw is therre to block a tooling hole made during manufacture of the head. It is not ever meant to be removed. My 2V engine '00 model has a cap head screw in that position on both H and V heads.
I agree, your head nut is rather corroded. It might be difficult to remove it without without backing out the stud? The nut might be corroded onto the stud threads. Plus, you'll need to remove all 4 nuts since you shouldn't just back off one because the head might warp.
Hmmm. Interesting assessment. The screw is not fully seated, which would indicate that it adjusts something, or is it supposed to be fully seated, and mine just isn't?! What you're saying is, of course, completely plausible, it just seems strange that a by-product of production with no utility whatsoever would be threaded and then filled with a screw. Why not just spot weld it shut and avoid the production complication? Unless it does have something to do with emissions/air injection or pressure regulation? I'm certainly not saying that you're incorrect, but I'm just not ready to write it off that easily. Even a plugged fuel/air idle screw in a carb does have a purpose. It's just plugged for govt regulations to prevent us fiddling with it. Maybe this is the same, and that's why yours has the plug? Who knows?
Maybe I'll try to find a fiche and see if an exploded view gives any clues. Or, maybe it's just one of those Italian-isms and it was just a hole that needed to be filled with something! In which case, I guess I should tighten mine down.
LoL...how on earth did you find that? My hat's off to you! That's seriously amazing that you found that guy! Thank you. It was driving me nuts. I just figured I'd stop by the dealership.
Mine was kind of loose. It turned easily, but I don't see signs of leakage. I'll keep an eye on it. If it's so useless, and it's prone to leakge, can we just weld it shut, or somehow permanently plug it?
Eh, whatever. I making way too much of this! Case closed. Thanks again.
If you're terribly concerned about it, and it is loose, I'd remove the srew. Obtain a same thread size screw in a hex cap head style alum material (to prevent steel /alum corrosion) clean out the thread in the head with acetone on cotton bud until it's completely clean then thread in the cap screw with thick permanent thread locking adhesive. By thick I mean one that can be used for small gaps, i.e. thread sealing. and also high temp. Torque the screw to no more than 5Nm i.e. finger tight with an allen key.
Hence, you get a nice new screw, no oil leaks and paranoia removed.