ORIGINAL: Sport_Pilot
...While I agree that they run better and seal better with castor, I don't buy that theory. Mostly because I have run with as little as 30% castor 70% synthetic with no problems except for hot restarts which started on the first tank and lasted to the last tank. Back to 100% castor and no problems.
Sorry Sport, that is fact, not theory. That you did not lose seal probably means that your engine is not nearly worn out. Castor in the pores does not make compression, it only restores it. Duke Fox used to advertise his Superfuel (29% all castor) for restoring some power to a worn out engine. It works on iron/steel only, not ABC.
Since the engines in question were apparently run extensively and their age means that they are probably iron/steel, some of their compression MAY be from the castor. The caution was to alert that IF the engine loses compression when synthetic is used, it might be restored by using all castor fuel.
The thing is that castor oil is thicker and doesn't vaporize. Has little to do with varnish.
Castor oil flashes at a higher temp than most synthetics. Before flashing it will thicken and form a protective varnish. This will SOMETIMES save an engine if you get off with a lean run.
The only reason to use so much oil in C/L is to improve the 4-2-4 break, other than that you can use the same percentages as R/C. One exception is the Fox Stunt. If you look at it you see it doesn't have much in the way of cooling fins.
The 4-2 break is primarily a function of timing through adjustment of porting (blowdown), compression (head shims), loading (prop size), fuel, and plug. The amount and type of lube you use is a matter of metalurgy and type of construction.
Many other early engines were also this way. Reduce the oil and it will get hot even when 4 cycling, especially with a cowled stunter.
This is true. One of the primary functions of the lube is to carry off heat.
Sometimes people get the same results using different observations so please don't assume this to be some sort of attack...just a different point of view.
George
Edit: Sorry, forgot to sign it.