It is stated that in cases where cylinder distortion produces exhaust valve leakage, the problem of valve burning becomes one of considerable difficulty. A flexible exhaust valve seat, which apparently conforms to the valve and produces a tight seat even though the cylinder head be distorted, has been designed and tested. Apparently complete sealing of the valve was secured in a cylinder known to be subject to exhaust valve seat distortion. This result indicates that heat dissipation through the seat is not of major importance when a tight seal of the valve is secured. The use of flexible inserts may remove some present limitations on cylinder design.