Heard a noise and thought it was a loose rocker. Tightened it down and fifty miles latter was back again so I tightened the rocker down again, went another fifty miles and bang!!! oil out the exhaust and stuck on the side of the high way. While waiting for the highway patrol ( No cell phones in the late 60's) pulled the head off and found exhaust valve sucked off stem bounced around in cylinder cracked cylinder wall toasted piston and bounced back through head. Not a good day