We've all read threads about engine oil level, in particular concerns about overfilling, and there have been some threads about oil level lights coming on. So, I have done some measurements on a set of engine cases I have here and calculations on oil volume.
My measurements are OK but volume calculations should be taken as approximate. As you read on, you'll find that less of a concern.
Sight glass checks... first of all if done by the book, "a few minutes", oil viscosity, temperature, etc. all come into play and results can be quite variable. Use a stopwatch if you want to be reasonably consistent... however, I will leave it up to you to determine where the sight glass level is if you have followed the manual, filled your oil with the 4.0 L/4.23 US Qts, and have changed the filter (with the OEM short one).
I can only offer you that I usually put in 4.2 L with a long filter change (technically an overfill by the book). I find my oil level at the top mark in the sight glass, and when cold, goes over the top of the sight glass. I would prefer all my fluids to be at their max value, just me. Observation is, when the engine is started, the oil level drops to the bottom of the sight glass, maybe below, as the engine immediately circulates the oil. YMMV, which is OK.
Others have found that when they fill with a gallon jug (3.8 L), they get an oil level light when starting/running from cold, which may go away once the oil warms up and expands... technically an underfill situation. YMMV.
The concern when there is an overfill, how much is too much and we're basically concerned about oil level so high it contacts the counterweights of the crankshaft, which can cause foaming of the oil, loss of pressure, etc. Naturally, we don't want that.
The pics I've taken are looking at the lower engine case from the sight glass/oil filter end. The first photo is with crankshaft in place, and I marked a red line where the bottom of the counterweight is. I measured this to be 36mm above the Top of the sight glass. I roughly measured the surface area of oil would be 90 square inches. Basically, 125 cu. in. of oil in that 36mm depth, 2.05 L/2.16 US qts. This would be the amount of overfill required to have any contact with the crankshaft, bike on centerstand. On the sidestand, likely half that overfill, maybe less.... but keep in mind the minute you start the engine, the oil level drops an inch.... roughly speaking. I do not know the lean angle on the centerstand, or I could estimate much closer.... the excess oil would run into the stator housing first..... so, let's not speculate too much, again, it matters little really.
A further calculation, the distance between the sight glass marks is 14mm/0.4" approx., and 90 square inches calculates out to approx. 2/3 a litre or quart, or if you like a healthy half. You can decide next time you fill with oil and see what the difference is between being at the lower mark or the top one.
So any of you concerned about overfilled by half a quart should simply relax and not get all concerned about draining out a few ounces......
Pic with crankshaft in, taken so you can see the red line I marked:
Pic taken with crankshaft removed, taken as to be in line with the sight glass as best I could. Well, you get the idea, mark is 36mm higher than top of sight glass:
This pic with engine case flipped over, in the middle is the sight glass opening, and red mark shown previously is on the outboard face of the casting, at the level of the machined boss/bored hole just south of it.
