Read the article in the link below. It speaks of a never change the oil engine in a lawn mower. Mowers have no oil filters, operate in dusty conditions and are air cooled which means cooling may not be optimal. The way Briggs does this is by using automotive style engine parts and tolerances. So much for this factory feeling that acid builds up over time or the oil wears out. I don't know what they think of regarding dirt in the oil.
http://archive.jsonline.com/business/new-briggs--stratton-lawn-mower-engine-never-needs-an-oil-change-b99433283z1-290423731.html
