Use any 10 - 40 W oil. You can also use a single grade 40 W oil if the mower is old and much used.
According to alldata the recommend grade of oil is 5w30.
four stroke motorcyle oil
10w30
5w20
best is 20w40 grade engine oil.
10w40 motorcycle oil only.
The oil grad should be printed on the oil cap (under the hood of your vehicle).
I use Honda 10w40 oil in our Polaris Sportsman 500. The only reason for the Honda oil is that I also own Honda motorcycles so I run the same oil in the bikes and the two quads. (We also have a Kawasaki ATV) Check the owner's manual for the specific grade of oil which should be used in your particular machine. The temperature range in which the machine is operated in is what determines the grade of oil to be used.
on top of oil filter plate it has one wire
15-40 W motorcycle engine oil grade JASO-MA.
Remove skid plate 12mm bolt
The oil filter is on the right side (as you sit on it) of the engine. There is an access plate with three screws holding it in place.