The main bearings from honda (new) ranged 0.0008"-0.0018", and the worn-out state is 0.0032", at which point it has trouble keeping the oil pressure up.
That all said: I have assembled this engine with as little as 0.0004" main bearing clearance. That one took a little while to break in (500 miles) with lighter oil (10w40), but it ran perfectly for 2 more years before I left that area to move to Colorado.
Essentially, if you have a non-new crankshaft, there are no bearings available from honda that will be too tight. The "optimum" clearance is Honda's best guess at a good all-around engine performance, for riders who might run too-light or too-dirty oil, and run at redline too much or lug the engine at low RPM too much. That clearance range is 0.0008"-0.0012", and the engines generally settle in at about 0.0016"-0.0018" after about 10,000 miles and run their best. I run mine tighter (quite a bit tighter) because I like to have higher oil pressure (so does this engine, so use 20w50 oil in it).
If the engine spins freely when bolted together with the bearings, it will run, and usually without problems. The oil is fed at 50 PSI by about 1500 RPM (about 15-30 PSI at 950 RPM) in the K2, approaching 60 PSI by 4000 RPM.
Honda's manufacturing 'rules' were set up so that the largest bearing journal, combined with the smallest bearing shell, would not make an engine that would not run: if the largest journal were place inside the tightest mainbearing, it made the clearance 0.0004", which is the same as the piston clearance used in the famous Honda 90 and 100cc engines. Roadracers I knew always went to tighter bearings for racing, not looser ones (like dragracers seem to do...), and they never had troubles, either. So, I seriously doubt you will, either.
