I am putting a new (stock) cam in my '92 xr600r after losing the original cam and four followers to what looks like a lack of oil in the head. I have checked all the lines, passages, screens and filter and am putting a brand new pump in. I did not find any obvious problems so maybe it was just low on oil at some point. My question is the centre plain bearing. The head is scored in the centre bearing area and the clearance, with plasti guage, is .006" on the bottom and .005" in the top cover. This seems excessive to me? Does anyone know what it should be? Can I, or should I, plug the oil hole in the centre journal of the cam? I am concerned that with the clearance, excess oil flow out the centre may starve the followers and cam lobes? It seems a bad bit of engineering to have two ball bearings with a plain bearing in the middle. Does the cam shaft flex that much that it needs a third bearing?