The aircraft was being flown to calibrate the stall warning device. The pilot closed the throttle and as the airspeed reduced to about 70 knots the propeller stopped. Attempts at restarting the engine were unsuccessful. The pilot elected to land on the beach where the aircraft struck soft sand. The right main gear collapsed and during the subsequent swing to the right the aircraft struck bushes at the edge of the beach. External examination of the engine revealed that rotation of the crankshaft was rather stiff, however this could have been the result of striking the beach sand during the landing. The engine was not stripped as the owner indicated that he would not return it to service. This accident was not subject to an on site investigation.