For some of the very early rigs I have seen graphite and tallow suggested as a gear box lubricant. Lubricating oils have come a long way since then!
When asked about a lubricant for a 1920s Ahrens-Fox, Ted recommended an SAE 140 gear oil, Doug recommended a 1000 weight gear oil; they are both right, because there are a half dozen different scales for measuring oil viscosity. For instance, an SAE 50 engine oil is equivalent to an SAE 90 gear oil. Doug’s 1000 weight was in ISO units which is about SAE 250. Ted’s SAE 140 will provide adequate lubrication, but may leak more than the SAE 250 plus will probably be easier to get from a lubricant supplier. However, no matter what you use, you want to avoid any lubricant with EP (extreme pressure) additives which can attack brass and bronze in the gear box. (The above applies to the early rigs.) Also note that engine (crankcase) oils are different than gear oils; they have different chemical contents.
— Tim W. Elder, Louisville, OH
Silver Trumpet – 2014 Vol. 3