RE: Options for castor oil?
I'm a little late with this post, having just strolled by this stringcouldn't resist putting in a comment. Six years ago I bought a considerably used .40 OS FP and made a head for it. I have given heavy use to that engine every season, hauling a 12X6 on a self-designed cardboard wing plane. That engine has never seen a drop of castor oil. I've run various types of motor oil but settled on 15W-50 synthetic mixed half/half with modified olive oil at 20 to 22% of the total fuel mix. The 15W-50 gives a nice seal and the modified olive helps keep things clean. The FP is perfectly happy with 25% ether and will, with a little coaxing, run ok on 20% as long as the ambient temperature is above 50F (10C).
People who don't know any better shriek in horror when I say this but: glow engines run more safely on castor; diesel engines don't need it. Unless you're running way over compressed (which will destroy your engine in short order no matter what the lube), a diesel won't get hot enough to ever need the polymerizing protection of castor. If you don't mind an oily hand, put it in front of the exhaust while running. . .it's hardly warm. Virtually all of the oil gets spit out, carrying some of the modest amount of combustion heat that is generated with it. Don't even think about putting your hand in front of a glow exhaust.
My .40 FP gets torn down at the end of each season for inspection. While six years of heavy use has caused some wear and reduced compression in this engine, there is no sign of galling on the piston and the rod has no slop. Similarly, the plain bearing/crankshaft has no significant play. I know that European readers won't be surprised by any of this; many of them used motor oil a few decades ago without any consequences beyond needing to clean the head now and then.
I also run an Enya .25 diesel and a couple of converted Norvel .061's (the latter on 40% ether). None of them have ever had castor fuel and all have a few years of running on themjust not as many years as that old used .40 FP. The only exception I can think of for any of this is the correct fuel mix for racing dieselswith minimum lube and lots of kerosene plus the sometimes addition of some fairly toxic cetane enhancers, these nasty little beasts do get hot, and castor might be a good idea for them.
A footnote: discussions about converting olive oil can be found by searching this forum and the fuel forum.