Originally Posted by ATLDB
Wonder how you can measure how much oil goes into your motorcycle via the sight glass? 1/2? 2/3?.
The "manufacturer" of this motorcyle design, built, tested this engine to run with 4 quarts of oil. Done, That's it, I don't care how cooler, hotter, lighter, heavier the bike will run with .71 or .69, or even .00000003 quarts less in the engine. When telling someone new how much oil to put in would it not be safer, easier and a lot less 1/2? 2/3? measuring of a sight glass you can't even reach, if they just put what the "manufacturer" tells them to.
Ah, if life were always so simple.
BMW didn't design this bike around the concept of 4.0000 qts of oil in the crankcase (and if they did design for a specific oil quantity, wouldn't you expect it to be in liters, as in 4.0000 L)?). Besides, after the initial fill, you'd never know how much is in the crankcase, even if you put 4.0000 qts in, due to the residual left behind when the cranckcase has drained. People attach far too much significance to specific numbers without considering either the objective or the tolerance range surrounding the specified quantity. In fact, "just put in 4 qts" during an oil change will, on many (most?) bikes result in the oil level being out-of-sight high.
A far better indication of what BMW "designed" the engine for is built into the side of the engine -- a sight glass that includes BMW's desired oil level within its indicating range. You won't find much better proof that BMW doesn't want a specific volumetric quantity thrown in without regard to the actual engine needs. Instead, they want you to ensure the oil level is within a specific range, defined by the sight glass, i.e., within a +/- tolerance represented by the top and bottom of the circle in the sight glass.
So, the original suggestion of 1/2-2/3 of the sight glass remains good newbie guidance (particularly for new engines, which will burn off a bit of oil during the first 10-15K miles of break-in -- 2/3 provides a bit more "buffer" in case the newbie doesn't check the level often).