When you go to Cunnings next time have a good look at the B&S mowers.
On the side there is a sticker stating that the engine is EPA compliant for X years or until Y.
Most times it will only be 3 or 4 years by which time it will be illegal to be used in a few USA states.
So if the mower can only be used for 3 or 4 years and remembering a mower only does about 50 hours a year, not hard to make a mower that will never need an oil change.
I have a shed full of B&S moweres that never needed an oil change,,,,,,,, till it was too late and some are better than 15 years old.
