With a poppet valved single acting uniflow steam engine what oil should be used in the crankcase? The valves don't need lubrication so can the cylinders be lubricated via the sump oi, eliminating the need for injecting lube oil into the steam line? What was the procedure with the later Sentinel engines?

Hi Alun. My experience with single acting engine ( Pearson - Cox 3 cyl) was to use a non emulsifying oil as used in Sentinel sumps, otherwise you will end up with gallons of Mayonaise? but not nice tasting!!! Les

Hi Alun, I am a double-acting steam engine "believer" myself, but from what I have read the best oil for single-acting steam engines is non-detergent (ND) oil, "40W SAE" rating. Peter Barrett used 30W non-detergent synthetic oils in his single-acting steam engines. I think that "Mobil One SHC634" synthetic oil would be good, as it is now used in many steam cars at 700F steam temperature, and judging by the manufacturer's specifications is good to a much higher temperature, and it is non-emulsifying with water, as noted by Les. This oil is available from mcmaster.com. There are also a number of 40W "ND" mineral-based motor oils available in the US, which I think would be good for single-acting steam engines, but I do not know about their availability outside of California! Peter Barrett tried splash-lubrication of cylinders from the crankcase, but reported that this was not successful because steam engines run with positive pressure in cylinders at all times, unlike IC engines which develop suction/vacuum during intake strokes. As a result, Barrett began injecting oil into the cylinders, through the inlet valve guides, and reported excellent cylinder lubrication with this method. Oil can be injected directly into the steam line to engine -- the "classic" method -- also very successful.

Peter