I recently built a four-cross back wheel for the first time--it's on an old but nice high-flange Campy hub that had originally been spoked four-cross. Using a new Mavic clincher rim, I built it just the way you'd build a three-cross wheel, except that I moved the crossing spokes over an extra two holes to get the fourth cross.
As in building a three-cross wheel, I started with the first drive-side spoke to the left of the valve hole. When I was done lacing the wheel, though, I noticed that instead of ending up between one of the nine pairs of nearly-parallel spokes on the wheel (it's a 36-spoke wheel), as on a three-cross wheel, it's offset by one hole, so it's between two spokes that converge as they move from the rim toward the hub.
"Bummer," said I to myself. "I'm going to have to take it all apart and relace it with everything shifted one hole clockwise to get the valve hole to come out in the right place."
But then when I started thinking about it--and believe me, I sat and stared at the wheel for a long time--I realized that you CAN'T shift one hole clockwise, because the spoke hole to the left of the valve hole is offset above the rim center line, and the spoke hole to the right of the valve hole is offset below the center line. So if you offset everything by one spoke, you'd be taking a spoke from the top flange (as you sit lacing the wheel on your lap) and threading it into one of the spokes below the center line, and that every spoke from then on would be in the wrong position relative to the rim. Of course, you could offset by TWO spokes, but that leaves the valve hole in the same position it it now, just on the other side of the two parallel spokes.
What the hell? I went back and looked at the old rim--a 70-'s vintage Mavic tubular rim--and noticed that the valve hole is in a different position: the spoke hole to the left is offset BELOW the center line and the spoke to the right is offset ABOVE it.
So it appears to me that if you four-cross a standard modern rim, configured so the spoke to the left of the valve hole comes off the top flange (I assume that's the current industry standard, because all the wheels on my other bikes are drilled that way, too) you've got to live with the valve stem in a less-than-ideal position. I think it's going to be possible to fit a pump head in there, but it still bugs me.
I guess this just caught me by surprise, and I'm wondering how others who build four-cross wheels deal with it. Can you order wheels with the valve hole correctly positioned for four-cross lacing, as it was on the old tubular rim? I'd never heard anything about that. I suppose I could cover the factory valve hole with a piece of tape and drill another one elsewhere, but that seems pretty half-assed. Or I could buy a new set of spokes and relace the wheel as a three-cross, but I don't really want to spend the 50 bucks on that either (I also bought spokes for the front wheel, which I haven't started on yet.)
Any experienced wheelbuilders have any comments or suggestions? I'm obviously not the sharpest tool in the shed in this area.