With the engine running you should see oil flowing from the curved overflow tube at the center of the shaft, if you don't, you’re not getting sufficient oil to the shaft.
The rocker shaft is made of two identical hollow pieces. The shafts fill with sludge which restricts oil flow. To minimize confusion when you disassemble the shafts and rockers, lay them out in sequence on an old towel. Clean all parts thoroughly with cleaning solvent and brush then place them back in sequence on the towel. You can get all the sludge out of the shafts with solvent and a wooden dowel slightly smaller in diameter than the inside of the shafts. If the shafts are badly worn, don't bother cleaning them, get new ones.
