EDIT: Sorry I posted this topic again, but still looking for a "scientific" answer other than "Honda says so".
I know this topic is beat to hell, so forgive me. I know most motorcycle manufacturers don't like oil with moly or graphite in it because weak clutch designs slip just well by themselves (tests have shown that moly and graphite don't hurt good clutches). I'll concede with that limitation considering the viable chemical alternatives.
However, why the hell does my owner's manual tell me not to use castor-based oils? It seems no one has noticed that point in the owner's manual on the other threads, and that is what everyone likes to run (including myself). That's what is in the full-synthetics and racing oils (I know why we don't run racing oils on the street), so I'm clueless to the justification. I know those nice, long chained molecules are going to start falling apart long before the recommended interval - not to mention the shearing and shock loads from the gearbox. Not wanting to blow my warranty by using unapproved oil, I'll hang my head for now, and change it all the time until the warranty is up, but I would like a good reason not to use the good stuff (if it rev's to the moon and runs for 40K miles without breaking, who cares if it is $13 a quart!).
Last edited by crzdriver; 04-11-2007 at 1:05 AM.
How about that castor oil can turn gummy after a short period of time; which makes it nit very suitable for any vehicle where the oil could be in the engine for any length of time. The oil can also breakdown from age.