ORIGINAL: Marcol
If the previous owner had used a quality synthetic oil based fuel the engine would be like new , inside and out.
I'm sorry but after running all my engines on this fuel
http://www.westonuk.co.uk/index_045.htm for the past 5 years I just don't subscribe to the castor oil is best debate.
The engine might be ok for a hack model, but it looks like it's done its best for its previous owner.
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Castor varnish comes off during cleaning. Under it lies the "protected" metal. Without a protective coating of castor grime, the metal is exposed and wears away (sides of the piston - obviously). Give me castor oil every time.
There is no way to determine the condition of the engine with it being that dirty. Disassemble, soak in slightly warm anti-freeze and then carefully reassemble with lots of oil. Put a new glow plug in it (recommended range) and a well balanced prop of the proper size and then give it a go. Chances are it will have many more flights left in it (unless you saw major scratches on the cylinder liner).
The anti-castor movement appears to be based strictly on obsessive/compulsive "dirty feelings" (no empiracal data) and nothing more.
Ed Cregger