Greasers! You know who you are. If your A&PIA sees the 10, or 14, or 18 zerk fittings on your engine and says, "that's all you have to do??" then find another who is qualified. On certificated aircraft, always adhere to the manufacturer's recommendations. For additional vintage airplane documentation and information, please join and contact AAA/APM. Following are some popular engines which require manual lubrication for which the originally recommended rocker box grease may no longer be available. Have a qualified A&PIA determine whether Jewell Amber Oil Rocker Box Grease is suitable for yours.
Most aviation engines designed or built before about 1931 had no provision for running oil to the valve train. This was not because it was an unheard-of practice to run oil upstairs, but because aircraft engines run at high loads continuously, it heated the oil too much. Improvement in cylinder head design and oil cooling in the early 1930's lead to engines where manual lubrication was no longer necessary. Owing largely to the Great Depression, re-tooling was too costly, and many early designs lingered in production through much of the early 1930's.
So called low-melt #2 greases were, and still are a popular substitute, and have a drop-point of about 430f. This is where they slide off a heated screw driver for example. What they leave behind when they "melt" is a useless film about like WD40. This is because the base oil is too thin. When it cools, the base and the grease do not blend again. Of course we now know that oil is the best lube upstairs, but that is not practical in most early rocker boxes because it just doesn't stay where its put for long enough. Genuine rocker box grease is basically gooey sticky oil, and if heated to drop point will resume its original consistency.
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