Engine valves must operate in engines with very low failure rates. Long-term durability testing is expensive. This cost could be reduced by running only a final successful proof test, provided adequate data existed to demonstrate that potential life and failure modes have been identified and eliminated by short-term tests and analysis.This approach was applied to a 1983 DDA Model 4-53 engine valve. The results are used to estimate valve life and, further, to estimate the effects of tolerance variations on valve life.The techniques used to determine valve temperatures and strains at nominal and unusual operating conditions in firing engines are presented. The experimental study shows that combustion strains and closing strains are caused by two different loading conditions which affect different portions of the valve head, and also shows how these loads vary with their governing parameters. The theoretical basis for these observations and trends is also presented.