Reread the first 3 sentences of the second paragraph of the post you quoted.
The pic is out of my CRF250X manual... The 250manual calls for the same oil as the 919, the 250 is a much more demanding motor on oil than the 919 will ever be, but still allows for higher viscosity's, and thus 15w40 IMO can be safely used without probs. the 15w will be a lil thicker when cold but will become the same viscosity when heated up down the road 2 min vs any 10w40.
Yeah, you said you "looked in the book to do the oil on my 919 and saw it called for the same exact oil as my 250". Except your 250 lists 15W40 and the 919 does not. Not exactly the same, right? Not trying to bust your balls but you sort of implied I'm an idiot
I figure the engineers telling me what oil to use know more about my 919 and oil than I do. Maybe some here know more than the Honda engineers.
Using 15W40 is probably perfectly safe and I don't pretend to know why it would be or wouldn't be. I'm just satisfied to use what the Honda engineers say I should use and don't feel the need to save a few bucks by second guessing them. Saving a few bucks seems to be the primary motivation for using 15W40 diesel oil. I don't doubt it's good shit but it's definitely not designed for a motorcycle. I'm sure diesel truck engines and my 919 have a lot of similarities but obvioulsy some differences as well.
I am curious though. A lot of people say something like "I've used XYZ oil and haven't noticed any problems". What kind of problems would you expect to notice, catastrophic failure, slipping clutch (common with energy conserving oils), microscopically measured increased wear on internal engine or tranny components, slightly increased oxidation on internal engine or tranny components? Point is most "problems" would require engine tear down and close examination with microscopes and/or micrometers to detect.
Carry on, just stirring the pot.