Machine-gun Lawnmower

When you want to turn over some very large engines, like the ones in large bulldozers, you insert a shotgun shell in a port and fire it to initiate the cranking process.

Thinking along these lines, I reason it should be possible to design an engine for a lawnmower (and other small- engined machines, such as motorcycles) using a belt-fed machine-gun with the firing chamber angled slightly to push the crank/flywheel around. A series of vaned ports on the flywheel/crank can be used as firing chambers.

The use of blank ammunition only, to ensure minimal damage to the engine; a hopper to catch the spent brass and a trigger mechanism hooked to a rheostat to allow faster or slower mowing, as needed. Maybe a grinding wheel and mild steel feedstock, under the front edge of the blade guard, to simulate muzzle flashes.

Then, every Saturday afternoon, suburbia erupts with the sounds of sustained small arms fire, as attentive husbands and gun nuts hose down their lawn with machine-gun fire, mowing the grass down in rows.

Of course, if you're American then you can use the Gatling version, which allows you to mow the grass at high schools and around Post Offices, using live bullets to cut the grass.