Last year the horizontal pushrod on number 1 exhaust fell out? and got bent. On inspection with a replacement rod, I noticed that the rod on the exhaust side, was virtually in contact with the aluminium sleeve and there was a witness mark on the bent rod at this point (which obviously could have occurred after it fell out). The rocker sat central on the valve stem, so that was in the correct position. I did have the head rebuilt about 5,000 miles ago with new valves, guides etc; one job was swaging the sleeves firmly into the rocker covers, so this could have brought the sleeve nearer the rod. Looking at the other rods most are not central in the sleeve due to casting tolerances. Because of the head rebuild I thought a sticking valve unlikely and compression is fine; so made a shim washer for the rocker shaft to move the rocker further from the sleeve (20 thou. thick). Sorted I thought.
Today it happened again, same valve. Before I take the head off is there any useful experience out there?