I just finished rebuilding an F2 head (twice) that has the "high performance" CycleX valves with a coating of some kind on them. After the engine was run a couple of hundred miles, this [thick] coating wore off the stems and left the valves very loose in their guides. The clearance had started at .0010" intake and .0020" exhaust: by the time the head came back to me they were nearly .0060" intake and even more on the exhaust side. I had to remove the valve guides, which had just been resized using bronze liners, and replace them with oversized CycleX guides because after I finished polishing off the REST of this coating, the valve stems were slightly below Honda's new-spec size.
Once all the rest of the coating was removed from the valves, they look like nice stainless-steel ones. I polished their stems and faces smooth, sized the new valve guides to fit appropriately, and will be sending the head back into service.
I don't know what the coating is/was, but it doesn't last long in the guides and it REALLY holds carbon tightly to the valve faces. It is about .0005" to .0008" thick on the surface, so when it wears off in the guides it adds about .0016" extra clearance, quick. 
You ever see that CycleX article that says you're wrong and the machine work you did was inferior?
http://cyclexchange.net/Fact%20or%20Fiction.htm
This cylinder head was sent to us to install on a customers motor.
Coincidentally, this cylinder head was done by the same person that questioned all valves with nitrite coatings or black diamond coatings. (Above mentioned forum gibberish)
If you look closely at the photos, you will see used valves that have been reground by a shop that needs a new valve grinder. Check out how choppy and uneven the lapping lines are.
Secondly, the valves seats have the same chatter, choppy and uneven finish.
Thirdly, these valves have clearly lead a hard life and should have been replaced.
Also, take a look at the dirt removed from the inside of the valve guide. So, this guy had a problem with some nitride valves? Maybe he should clean the engine components before assembly.
The exhaust guides are worn and should have been replaced.
Summary: The only new items in this cylinder head were the valve seals. this head was assembled with the 40+ year old valves, guides, springs and all should have been replaced.
Worst part, the customer was charged almost $700.00.
Curious your response.
Yeah, Ken actually called me one day at my old job to ream me out for this post.
But, the truth is, I relayed my experience verbatim as above. It cost me a small fortune to rebuild that guy's head with new guides, seals, etc., and I lost every cent in the transaction. I told Ken the same thing when he called me: I had installed them with the clearance info he provided me with the valves. The customer was competent with his engine reassembly work. That's about all I can add to it, except Ken has been mad at me ever since, I think. He said the machine shop must have done something wrong with the clearance numbers, but I checked them myself before reassembly (the first time) and found them to be the same ones Ken gave me: this machine shop has installed a lot of coated valves in racing engines, too, so they had experience - and that was why I let THEM do it instead of me.
In the end, I don't know what happened to cause the guides to become so loose and have their odd larger top-and-bottom clearances after relatively few miles: it has never happened to me before nor since, but that was the only time I ever used "coated" valves. I do know that polishing off the remaining coating from the stems made for a good engine afterward, which ran for over a year and was sold in that cafe' bike for north of $10 grand after that.
