Adding too much oil can cause engine damage. Weed Eater brand 20-inch push mowers, built with Briggs & Stratton engines, require regular maintenance to ensure proper performance. When performing regular oil changes, use lawn mower engine oils with a viscosity rating of SAE 30.il Capacity. The oil capacity of the Briggs & Stratton 4.50 foot-pounds gross torque engine is 20 ounces. Adding too much oil, according Briggs and Stratton, can cause engine damage.