The basic unit

This includes the wheels, axle, frame, cutter head, blower, and perhaps the feeding apron and rolls (referring to conventional cylinder types).

The basic unit is driven by the tractor PTO, or by an engine on the harvester.

Power Drive Systems. The PTO drive consists of a long shaft extending from the tractor PTO spline shaft to a pulley on the basic unit. This shaft has two or three universal joints. The PTO shaft assembly should have no sharp bends. Adjustable standards are usually furnished on the tongue so you can raise or lower the PTO shaft.

Follow instructions in your owner's manual in setting up universal-joint shafts because older types can be assembled incorrectly. The yokes on both ends of the telescoping shaft must be lined up alike; otherwise uneven rotation occurs on turns.

The heavy flywheel mechanism of the harvester should clear the machine of cut forage after you stop the PTO shaft. To accomplish this most machines have at least one overrunning clutch.

The overrunning clutch is like the overdrive or freewheeling device on automobiles. When force is applied to the shaft small dogs or pawls "push" the driving pulley. But when the force is removed the dogs are moved toward their hub and simply slide around within the driving pulley (Fig.8a).

The overrunning clutch is a useful device. Some makers use it on the hay hold-down wheel. Usually the hay on the apron conveyer pushes the wheel. But if the hay slips the clutch catches and moves the hay along, assisting the conveyor.

The overrunning clutch on the windrow pickup permits the drum to stand still if you reverse the feed rolls when too large a slug of forage enters the throat.

(b)