If oil level in S40's sight bubble is at lower limit line (checked when engine is cold and bike is vertical), about how much oil is needed to "top" off to upper fill line?  thanks...

about 300-400 mL fron bottom line to top line. I do as OldFeller and just keep it a bit over filled. Just enough so I can barely see the line of oil in the very very bottom of the sight glass with the bike on the stand.

This is a good trick, really.

Now if you are afeared of "overfilling" -- do this little drill for me just one time.

Put it on the side stand the way you always leave it when you put it up for the night.

STONE COLD, fill it up until it jest barely peeks into view in the oil fill window ...

.... now ask you wife to come hold it completely upright and keep it there for you.


                              ! gasp !

                         Aaaaaugh !!

       the oil window is completely dark with oil

             I am overfilled, drastically !!



.... take a deep breath and trust in the Force, young Jedi

While the wife hold the bike upright, crank it while watching the oil window.

As soon as the bike cranks over the oil level drops to way way below the oil window.

Where did it all go?   Into circulation in the oil passages, the transmission, etc. etc.


----------------------------------------------------------


Next thing you need to know is that there is an oil splash shelf in the crankcase right over the top of the oil window that protects the crank from oil down in the sump splashing around during braking, cornering, hills etc.

So, what are the downsides to slightly over filling your bike so you can instantly see if you have "enough oil" just by glancing down at it while it is on the kickstand?

Dunno.   Haven't found any yet, personally.  
Got some other people helping me look fer them now, so if they exist we will find them.

I do like instant easy visible checks and I do like it that when I can see no oil in the window on the sidestand due to usage I can rock the bike to vertical and verify that I AM NOT LOW ON OIL to Suzuki's methodology.
 
I have lots of time to get her home and top her on up to my methodology -- you see, I pretty much know I will never run short on oil and kill my engine using my method.


Unfortunately, Suzuki's methodology has killed a lot of engines over the years due to low oil.


there is a poll attached to a tech post now

If you are an overfiller, please go vote

I think Suzuski tried to make fools out of us when they say to check the oil vertically,.....wondered just how many of us would stoop to that level (pun intened) I for one, didn't bite ! And now I think I belong to the "full" group. All you vertically minded are "underfillers"
We'll see who's crankshaft falls out first