Two warnings about cleaners, and I really mean it!
I've had simple green cause rapid oxidation on my aluminum engine that resulted in white powder raised through the paint over the entire engine. It was a real pain to remove.
I've had engine degreaser completely strip the stock paint off my engine. It was so good at it that I've taken to using it as my first paint stripping step. It was a specific engine degreaser from Kragen called "Foaming Engine Degreaser" and it even pulled off some of the stock frame paint!
I am still trying to figure out the best method to clean my bike. I imagine a good automotive grade paint cleaner would do it, but I won't use simple green or the foaming engine degreaser anymore if I just want to remove dirt.
One caveat on the simple green aluminum oxidation issue... the engine was very warm when I sprayed it on. Lower temperatures might not create the same result.
Regarding the nascent oil thread... seriously? I used to run used engine oil from my first car... mixed with brake fluid and coolant in my CB360T because I didn't have enough money for fresh oil for both vehicles. I've never run an oil that didn't actually lubricate the engine, and how many of us actually drive these bikes enough to be concerned about 50,000 miles of wear? I'm guessing less than 5%. So, run whatever the heck you feel like running. I run fully synthetic mobil one diesel engine formula, but I've also run the cheapest car grade, and the aforementioned concoction.
One other note on oil. I changed the oil on my buddy's bike. He just bought it and rode about 500 miles on it. The oil had not been changed in about three years, and there were only two cups or less of it in the engine. It was also the consistency of mud... and I am not exaggerating. Of course, it ran better with a fresh charge of oil, but at 35k and still going strong, I think it proves a point. He rides a Suzuki VX800. Oh, the fresh paint was fully synthetic Mobil One Diesel formula. The engine doesn't leak either.
Regards,
Camelman