An important thing to remember about valve adjustment intervals is to inspect your valve-train. This is especally critical with roller cams. The high lift and quick opening and closing ramps on a mechanical roller cam make the valve springs work much harder. Inspect each valve spring and retainer when adjusting your valves. Also, be extra leery of a valve that needs more adjustment than the others. It is possible that the bearings in the roller lifter may be "going away". Major engine damage will result if a roller stops "rolling"on the cam lobe
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--Mike