these bikes only have tranny oil the engine is lubed by the oil u put in your fuel, there should be a little glass window somewhere on the engine, there should be a mark in the middle of the window and you should be able to see that the oil is above that mark, if it aint drain it out and put some new in and make sure its above the mark but not right at the top of the window as im sure this can cause overheating or something
says 660 milliliters on the cover I believe. Just use my trusty ratio rite to dump it in and never bother checking. Still on my first clutch so eh must be doing something right. or I just need to ride harder...hmmm.
My 1980 rm250 has no window and no bolt to remove to check. Sucks because it was eating oil through the right crank seal (fixed) and leaking around the sprocket (fixed) so you can't just dump in the specified amount and go.