Engine for producing mechanical energy by internal combustion of a fuel includes a shaft and a crank arm attached to the shaft. The engine further includes a casing, where the interior of the casing forms a hollow cavity dimensioned to allow the crank arm to rotate within the hollow cavity and the crank arm is capable of making a seal with the interior surface of the casing to block fluid passage. The interior of the casing also includes a bypass area that allows fluid passage around the crank arm. A first valve is positioned adjacent to the bypass area and a second valve is positioned adjacent to the bypass area opposite from the first valve. The first valve and the second valve are configured to block fluid passage when closed.