I use whatever engine oil is in the basement by the drill press for use as cutting fluid. Currently that's half a bottle of semi-synth 10w30.

That it is oiled is important. Not terribly important what it's with.

Serves 2 purposes.... Prevents corrosion of steel parts, and provides initial lube during cranking. If using a petroleum oil (most standard motor oils) do be careful to keep it off rubber components, like the carb orings. It's really only needed on bearings, the crank, the crank pin, the wrist pin, and the cylinder/piston. If it was a 4 stroke, add to that the cam, pushrods and rocker arms.

J