a lawn mower blade mounted coaxially at the bottom of a vertical engine drive shaft is normally de - clutched from the shaft and stopped by a brake . when the engine is accelerated , the blade is released by the brake and clutched by a centrifugal clutch to the engine driven shaft . the blade carrier and clutch and brake drum are included in a compact assembly on a hub and mounted as a unit on the engine shaft . to replace the flywheel effect normally provided by a blade fixedly mounted on the engine shaft , the unitary assembly also includes a flywheel mounted on the hub . the assembly and flywheel are protected from blade cuttings by a protective bowl shaped to surround the flywheel and form a mounting platform for a brake band about the drum .