Some of you who have my book(s) will recognize the following:
In 1971, in response to the astounding success of the CB750, American Honda's (2) managers decided they were very important people, and they didn't like the way Honda wrote its Shop Manuals and Owner's Manuals, calling it "Jinglish". So, they simply announced that THEY were going to make all "...bulletins, owner's and shop manuals in American English..." and proceede to do so.
The catch: not one of the 'authors' of these translations spoke Japanese, nor understood it. They also were not mechanics, but were blowhard Californians who had become rich at Honda's expense and thought they were real important dudes. Well, they had half of that right...
When Japanese make a statement like, "...for richhness, turn screw in..." regarding carburetion, it is a statement organized as: "for [problem] do [solution]". This is why, for example, so many misunderstand that turning the idle-mixture supply screw inward on a CB9any bike) carb makes the mixture LESS RICH.
In the early CB750 owner's manuals, Honda provided a temperature chart showing very clearly that at temperature drops below 50 degrees F that one MAY use 10w40 oils. But it also clearly shows that above 50 degrees F that ONLY 20w50 oils should be used. American Honda's geniuses (I reiterate that the only wrench they had ever held was the one used to wrestle off a beer bottle cap) simply altered the statement shown on those diagrams to say "20w50 or 10w40" oils, and completely omitted the statement requiring "low detergent oil" later on those 2 pages of the manuals.
If you have, or can find (a non-AI-altered version of) a genuine CB750 Owner's Manual, you will see exactly what I am writing about here.
The shop bulletins, which originally came from Honda's headquarters via the Honshu discoveries where the CB750 was being built, suddenly changed appearance to look just like the one in the first post in this topic. They all showed "American Honda" at the top of the page. In the shops where I worked, and later in my own shop, we used to stick them on the wall with thumbtacks and throw darts at the "American" portion of the headline.
That is how the 750, and later the rest of the SOHC4 bikes and many Twins, came to suffer short bearing life. Foaming oil, caused by transmission teeth splashing and trying their best to whip the oil to death, make detergent foam. This makes oil pressure drop dramatically when the oil is hot because foam in oil breaks suction and the oil pumps cannot pull in enough oil per revolution, so oil pressure and flow drop.
A LOT.
