BoneHead,

Why do you think the engine is toast? It is normal for castor oil to cause a varnish buildup on top of the piston. This is easily removed. I would reassemble it and try it before replacing parts.

One item to remember is to use fuel with castor-only lube if the engine has a lot of time on it. On an iron/steel setup, as the piston wears, castor varnish replaces some of the tolerances and adds compression. If you use synthetic, it will clean out this varnish and you MAY have a compression problem. Not to worry, switching to all-castor will restore it through running. The castor content on that engine should be 25% to 28% for best service.

Good luck with it.

George