The well-known discussion on an engine consisting of a ratchet and a pawl in [R.P. Feynman, R.B. Leighton, and M. Sands, The Feynman Lectures on Physics, vol. 1 (Addison Wesley, Reading, Massachusetts, 1963), pp. 46.1-46.9] is shown to contain some misguided aspects: since the engine is simultaneously in contact with reservoirs at different temperatures, it can never work in a reversible way. As a consequence, the engine can never achieve the efficiency of a Carnot cycle, not even in the limit of zero power (infinitely slow motion), in contradiction with the conclusion reached in the Lectures. 1 Introduction Chapter 46 of The Feynman Lectures on Physics [1] contains a celebrated illustration of the impossibility of obtaining work from thermal fluctuations with an efficiency greater than that of a Carnot cycle. A careful analysis of a device that, at first sight, seems to lift a weight using the thermal energy of a gas, reveals that there exists in fact a dissipation which preve...