Originally Posted by bmwrench
My post about valve stem to guide clearance applies to Kibblewhite's "Black Diamond" parts, not OEM or other aftermarket parts, and only the exhaust side at that.
Yes, tight guide clearances, where they will work, are a Good Thing; better oil control and valve sealing, leading to longer-lasting valve jobs, less noise,etc.
Smokey Yunick said that he found tight guides causing power loss through oil suction. I think I know what he is talking about but is is hard to explain. He does a good job of it. Tight guides might also reduce valve seal because they don't allow the valve room to find the seat's center. I have never noticed any leakage caused by that while leaking down hot engines with tight guides but . . . . At any rate, the upside of tight guides outweigh the downside in our engines IMO.
I don't understand why you would run Black Diamond valves if you have to set up the exhaust guides well on their way to being worn out for them to work from brand new?