Have a look at the blade - its held on by a long centre bolt usually, with some sort of holding device that stops the blade spinning on the crankshaft. There should be a 'truth' mark on the blade - a circle visible where a washer has been. Some of these washers are sprung types, that prevent the main bolt from coming undone.
John
August 2009
I can answer this question...
briggs and stratton classic 35e blade dropped off "briggs and stratton"?