Yamaha RAPTOR YFM660R Owner's Manual page 274

NOTE:
_
The engine oil should be between the minimum
and maximum level marks.
_
4. If the engine oil is below the minimum level
mark, add sufficient oil of the recommended
type to raise it to the correct level.
NOTE:
_
When adding oil, be careful not to overfill the en-
gine oil tank; the oil level rises faster starting from
the half-level-portion on the dipstick.
_
5. Insert the dipstick into the oil filler hole, and
then tighten the oil filler cap.
CAUTION:
_
Make sure that the oil filler cap is securely
tightened, otherwise oil may seep out when
the engine is running.
_
8-19