most small 4 stroke engines (lawnmower engines) Briggs, Tecumseh etc will use a straight 30.
there's not much need for multi viscosity oil in those small lawnmower engines since the tolerance in engine clearances is not that big a deal as they are in today's car engines....
BTW, I took 3 years of HS autoshop...... in our 1st year of shop (the class was called Power Mechanics) we learned the fundamental theory of horsepower, torque, and the understanding the engine cycle (2 stroke vs 4 stroke) etc.....in that class each student had a Briggs and Stratton engine.....we had to completely tear down the engine to the smallest component and put it back together, we then measured the engine for actual HP and torque.... it wasn't an easy class for me, but I'm glad I took those auto-shop classes... I still change my own oil and perform routine car maintenance because of those classes... and the repairs I don't do my self, I have a general idea if a repair is actually needed by the shop and what it entails....
It's a shame that most schools no longer have autoshop classes in HS......
