a drive arrangement for selectively repositioning a discharge spout of an agricultural harvesting machine by rotating it about a substantially vertical axis includes a drive motor coupled to a driveline incorporating a slip clutch operable for interrupting power flow to the spout in response to the driving torque exceeding a predetermined threshold value so as to prevent damage to the spout and / or drive motor when the spout impacts or is driven against an obstacle . the overload clutch is constructed so as to resist spout movement after the clutch has interrupted the flow of power through the driveline and to automatically reestablish power flow once the cause for the overload no longer exists .